Machine drawing : includes AutoCAD [2 ed.] 9780071072946, 0071072942

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Machine drawing : includes AutoCAD [2 ed.]
 9780071072946, 0071072942

Table of contents :
Cover
Contents
PART A DRAWING FUNDAMENTALS
1. Introduction to Drawing
1.1 What is a Drawing?
1.2 Uses of Drawings
1.3 Elements of Graphics
1.4 Methods of Expression
1.5 Methods of Size Description
1.6 Methods of Preparing Drawings
1.7 Types of Mechanical Drawings
1.8 Drawing Standards
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
2. Computer Aided Drafting
2.1 Introduction to Computer Aided Drafting
2.2 Advantages of Computer Aided Drafting
2.3 Starting the AutoCAD Program
2.4 AutoCAD Opening Screen
2.5 AutoCAD Commands
2.6 Function Key Assignments
2.7 Short-Cut Key Characters
2.8 UCS and UCSICON
2.9 Coordinate System
2.10 Units
2.11 Viewing a Drawing
2.12 Drawing Aids
2.13 Object Snap
2.14 Drawing Basic Entities
2.15 Correcting Mistakes
2.16 Object Selection
2.17 Modify Commands
2.18 Modify Properties
2.19 Match Properties
2.20 Pedit
2.21 Grips
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Problems for Practice
3. Drawing Apparatus
3.1 Introduction to Drawing Equipment
3.2 Triangles
3.3 Ruler
3.4 Scales
3.5 Protractor
3.6 French Curves
3.7 Instrument Box
3.8 Stencils
3.9 Inking Pens
3.10 Drawing Sheet
3.11 Types of Paper
3.12 Drawing Sheet Fasteners
3.13 Pencils
3.14 Drawing Ink
3.15 Eraser
CAD 3.16 Equipment for Computer Aided Drafting (CAD)
3.17 Computer Software
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
4. Lines and Freehand Sketching
4.1 Lines
4.2 Precedence of Lines
4.3 Thickness of a Line
4.4 Drawing Lines
4.5 Freehand Sketching
CAD 4.6 Lines Using CAD
4.7 Sketch Command
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Lines, Circles and Arcs
Problems for Practice
5. Lettering
5.1 Introduction
5.2 Guide Lines
5.3 Spacing between Lines
5.4 Width of Characters
5.5 Line Thickness of Letters
5.6 Spacing between Letters
5.7 Inclined Letters
CAD 5.8 Text Command
5.9 Mtext Command
5.10 Arc Aligned Text
5.11 Editing Text
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Lettering
CAD Assignment on Lettering
6. Basic Dimensioning
6.1 Introduction
6.2 Elements of Dimensioning
6.3 Dimensioning Circular Arcs
6.4 Dimensioning Diameters
6.5 Dimensioning Holes
6.6 Dimensioning Angles
6.7 Dimensioning Chamfers
6.8 Dimensioning Tapers
6.9 Dimensioning Undercuts
6.10 Dimensioning Repetitive Features
6.11 Dimensioning Equidistant Features
6.12 Dimensioning Threads
6.13 Dimensioning Curves
6.14 Dimensioning Methods
6.15 Placement of Dimensions
6.16 Sequence of Dimensioning
CAD 6.17 Layers
6.18 Dimensioning Commands
6.19 Dimensioning Methods
6.20 More Dimension Methods
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Dimensioning
CAD Assignment on Dimensioning
Problems for Practice
PART B METHODS OF PROJECTION
7. Orthographic Projections
7.1 Introduction
7.2 What is Projection?
7.3 Types of Views
7.4 Principle Picture Planes
7.5 Methods of Orthographic Projection
7.6 Hidden Details
7.7 Preliminary Decisions for Making a Drawing
7.8 Projecting Side Views
7.9 Projection of Straight Inclined Face
7.10 Projection of Circular Boundaries
7.11 Projection of Curved Boundaries
7.12 Understanding Orthographic Views (Blue Print Reading)
7.13 Missing Views
7.14 Some Drawing Conventions
7.15 Sequence of Drawing
CAD 7.16 Drawing Orthographic Views
7.17 Plotting
Thoery Questions
Viva-Voce Questions
Multiple Choice Questions
Assignement on Orthographic Views
CAD Assignment on Orthographic Views
Homework
Problems for Practice
Assignment on Missing Views
Problems for Practice
8. Sectional Views
8.1 Introduction
8.2 Types of Sections
8.3 Conventions in Sectioning
8.4 Section Lines (Hatching)
CAD 8.5 Hatching using AutoCAD
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment 1 on Sectional Views
CAD Assignment on Sectional Views
Assignment on Half Sectional Views
CAD Assignment on Half Sectional Views
Problems for Practice
Diffi cult Problems for Practice
9. Auxiliary Views
9.1 Introduction
9.2 Types of Inclined Surfaces
9.3 Drawing Auxiliary View of an Inclined Surface
9.4 Drawing Auxiliary View of a Curved Surface
9.5 Illusions in Auxiliary Views
9.6 Skew Surfaces
CAD 9.7 Construction Lines
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Auxiliary Views
CAD Assignment on Auxiliary Views
Problems for Practice
10. Axonometric Views and Oblique Views
10.1 Introduction
10.2 Types of Pictorial Views
10.3 Axonometric Views
10.4 Isometric Scale
10.5 Drawing Isometric Views
10.6 Projections of Non-Isometric Lines
10.7 Isometric View of Angles
10.8 Isometric Drawing of Circles
10.9 Isometric Drawing of Arcs
10.10 Isometric Drawing of Curved Objects
10.11 Isometric Sections
10.12 Dimensioning Isometric Drawings
10.13 Reversed Isometric
10.14 Dimetric Projections
10.15 Trimetric Projections
10.16 Oblique Projection
10.17 Drawing an Oblique View
10.18 Cabinet View
CAD 10.19 Isometric Grid
10.20 Isocircle
10.21 Viewports Command
10.22 Types of 3D Models
10.23 User Coordinate System (UCS)
10.24 Views
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Isometric and Dimetric Views
CAD Assignment on Isometric Views
Assignment on Oblique Views
CAD Assignment on Oblique Views
Homework
Problems For Practice
11. Perspective Views
11.1 Introduction
11.2 Terminology
11.3 Factors Affecting Appearance
11.4 Selection of Parameters
11.5 Types of Perspective Views
11.6 Drawing a Perspective View
11.7 Perspective View of a Cylinder
11.8 Drawing a Perspective View of a Circle
11.9 Graticulation
CAD 11.10 Rays
11.11 Dview Command
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Perspective Views
CAD Assignment on Perspective Views
Problems for Practice
PART C JOINTS AND COUPLINGS
12. Riveted Joints
12.1 Introduction
12.2 Rivets
12.3 Making a Riveted Joint
12.4 Classifi cation of Riveted Joints
12.5 Joint Proportions
12.6 Applications of Riveted Joints
12.7 Structural Joints
12.8 Boiler Joints
12.9 Light Work Applications
CAD 12.10 Block
12.11 Creating a Block (Block Command)
12.12 Retrieving a Block (Insert Command)
12.13 Inserting a Block at Many Places (Minsert Command)
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Riveted Joints
CAD Assignment On Riveted Joints
Homework
Problems for Practice
13. Threads
13.1 Introduction
13.2 Terminology
13.3 Classifi cation of Threads
13.4 Thread Profi le
13.5 Pitch of Thread
13.6 Thread Designation
13.7 Specifi cations of Threads
13.8 Thread Representation
13.9 Internal Threads
CAD 13.10 Array Command
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Screw Threads
CAD Assignment on Screw Threads
Homework
Problems For Practice
14. Bolts and Nuts
14.1 Introduction
14.2 Terminology
14.3 Bolt Proportions
14.4 Drawing a Bolt/Nut
14.5 Studs
14.6 Screws
14.7 Locking Devices
14.8 Special Nuts
14.9 External Locking Devices
14.10 Spring Washers
14.11 Bolts and Nuts for Special Applications
CAD 14.12 Wblock Command
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment 1 on Bolts and Nuts
Assignment 2 on Locking Devices
CAD Assignment on Bolts and Nuts
Homework
Problems for Practice
15. Welded Joints
15.1 Introduction
15.2 Types of Welding Processes
15.3 Types of Joints
15.4 Edge Preparation
15.5 Symbols
15.6 Specifying a Welded Joint
15.7 Fillet Welds
15.8 Groove Welds
15.9 Spot Welds
15.10 Seam Welds
15.11 Plug Welds
15.12 Surface Welding
CAD 15.13 Graphic Library
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Welded Joints
CAD Assignment on Welded Joints
Homework
Problems for Practice
16. Shafts, Keys, Cotter and Pin Joints
16.1 Shafts
16.2 Keys
16.3 Types of Keys
16.4 Splines (IS 2327:1991, IS 3665:1990, IS 13088:1991)
16.5 Cotter Joints
16.6 Knuckle Joint
CAD 16.7 Solid Modeling
16.8 Solid Modeling Commands
16.9 Operations on 2D Objects to Convert to 3D Objects
16.10 Operations on 3D Solids
16.11 Composite Solids
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Keys and Joints
CAD Assignment on Keys and Joints
Homework
Problems for Practice
17. Couplings and Clutches
17.1 Couplings
17.2 Muff Couplings
17.3 Rigid Flange Couplings
17.4 Flexible Couplings
17.5 Parallel Coupling (Oldham’s)
17.6 Universal Coupling
17.7 Constant Velocity Joint
17.8 Detachable Couplings
17.9 Slip Couplings
CAD 17.10 3 Darray
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Couplings and Clutches
CAD Assignment on Couplings and Clutches
Homework
18. Pipe Joints
18.1 Pipes
18.2 Pipe Materials
18.3 Pipe Designation
18.4 Pipe Threads
18.5 Types of Pipe Joints
18.6 Joints for Cast Iron Pipes
18.7 Joints for Copper Pipes
18.8 Joints for Wrought Iron Pipes
18.9 Joints for Lead Pipes
18.10 Joints for Hydraulic Pipes
18.11 Union Joint
18.12 Expansion Joints
18.13 Pipe Fittings
18.14 Cast Iron Fittings
18.15 Flanged Fittings
18.16 PVC Fittings
18.17 Valves
18.18 Piping Symbols
18.19 Piping Layouts
18.20 Pipe Supports
18.21 Tubes
18.22 Tube Joints
CAD 18.23 Multilines (Mline Command)
18.24 Creating a New Mline Style (Mstyle Command)
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Pipe Joints
CAD Assignment on Pipe Joints
Homework
Problems for Practice
PART D PRODUCTION DRAWINGS
19. Tolerances, Limits and Fits
19.1 Introduction
19.2 Terminology
19.3 Tolerances and Manufacturing Processes
19.4 International Tolerance Grade (It Grade)
19.5 Fundamental Tolerances
19.6 Placing a Dimension with Tolerance
19.7 Cumulative Tolerances
19.8 Fits
19.9 Systems of Fits
19.10 Specifying a Fit
19.11 Types of Fits
19.12 Selection of Fits
19.13 Fits for Thread Fasteners
19.14 Gauges
CAD 19.15 Putting Tolerances using CAD
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Tolerances, Limits and Fits
CAD Assignment on Tolerances, Limits and Fits
Homework
Problems for Practice
20. Geometrical Tolerances and Surface Finish
20.1 Introduction
20.2 Types of Tolerances
20.3 Terminology
20.4 Frame
20.5 Datum
20.6 Material Condition
20.7 Tolerance Symbol
20.8 Tolerance Value
20.9 Indicating Geometrical Tolerances on Drawings
20.10 Form Tolerance for Single Features
20.11 Tolerances on Related Features
20.12 Run Out
20.13 Surface Texture
20.14 Profi les
20.15 Surface Roughness Number
20.16 Roughness Symbols
20.17 Lay
20.18 Roughness Grade Number and Grade Symbols
20.19 Roughness with Manufacturing Processes
20.20 Roughness for Typical Applications
20.21 Rules for Putting Roughness Symbols
CAD 20.22 Geometric Tolerances
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Geometric Tolerances and Surface Roughness
CAD Assignment on Geometric Tolerances and Surface Roughness
Homework
Problems for Practice
21. Material Specifi cations
21.1 Intro duction
21.2 Types of Engineering Materials
21.3 Ferrous Metals
21.4 Designation of Steels [IS 1762–1974 Part 1]
21.5 Steel Designation According to Chemical Composition [IS 7598–1974]
21.6 Code Designation for Ferrous Castings [IS 4863–1968]
21.7 Non-Ferrous Metals
21.8 Plastics
21.9 Bill of Materials
CAD 21.10 Table Command
21.11 Block Attributes
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
22. Production Drawings
22.1 Introduction
22.2 Title Block
22.3 Manufacturing Processes
22.4 Heat Treatment Processes
22.5 Tooling
22.6 Inspection
22.7 Jigs
22.8 Fixtures
22.9 Assembly Drawings
22.10 Standard Mechanical Components
22.11 Production Drawing
22.12 Process Sheet
22.13 Title Block
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Production Drawings
CAD Assignment on Production Drawings
Problem for Practice
PART E MACHINE PARTS
23. Springs
23.1 Introduction
23.2 Classifi cation
23.3 Helical Spring
23.4 Leaf Spring
23.5 Conventional and Symbolic Representation of Springs
23.6 Diaphragm Spring
CAD 23.7 Helix Command
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Springs
CAD Assignment on Springs
Homework
Problems for Practice
24. Belts and Pulleys
24.1 Introduction
24.2 Belts
24.3 Pulleys
24.4 Types of Pulleys
24.5 Flat Belt Pulleys
24.6 Grooved Pulleys
24.7 Toothed Pulley
24.8 Rope Pulley
CAD 24.9 Autolisp
24.10 Specifying Variables
24.11 Extracting Data from List Variable
24.12 Get Commnads
24.13 Mathematical Operations
24.14 Angles in Autolisp
24.15 Logical Operators
24.16 Conditional Branching (If Command)
24.17 Looping a Program
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Belts and Pulleys
CAD Assignment on Belts and Pulleys
Homework
25. Bearings
25.1 Introduction
25.2 Classifi cation of Bearings
25.3 Hydrodynamic Bearings
25.4 Plain Journal Bearing
25.5 Plain Journal Bearing Materials
25.6 Sleeve Bearing Supports
25.7 Hangers
25.8 Rolling Bearings
25.9 Mounting of Rolling Bearings
CAD 25.10 Managing Entities
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Bearings and Supports
CAD Assignment on Bearings and Supports
Homework
Problems for Practice
26. Gears
26.1 Introduction
26.2 Terminology
26.3 Types of Gears
26.4 Gear Tooth Calculations
26.5 Tooth Profi les
26.6 Base Circle
26.7 Drawing Approximate Involute Tooth Profi le
26.8 Conventional Representation of Gear Teeth
26.9 Construction of Gears
26.10 Spur Gears
26.11 Helical Gears
26.12 Bevel Gears
26.13 Worm and Worm Wheel
26.14 Rack
26.15 CAD for Gear
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Gears
CAD Assignment on Gears
Problems for Practice
PART F MACHINES
27. Part and Assembly Drawings
27.1 Introduction
27.2 Detail Drawing
27.3 Assembly Drawings
27.4 Bill of Materials
27.5 Steps for Creating Assembly Drawings
27.6 Blue Print Reading
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Part and Assembly Drawings
CAD Assignment on Part and Assembly Drawings
Homework
Problems for Practice
28. Internal Combustion Engines
28.1 Introduction To I.C. Engines
28.2 Power System
28.3 Fuel System
28.4 Ignition System
28.5 Cooling System
28.6 Lubrication System
Multiple Choice Questions
Theory Questions
Viva-Voce Questions
Assignment on I.C. Engines
CAD Assignment on I.C. Engines
Homework
Problems for Practice
29. Steam Power Plants
29.1 Introduction
29.2 Steam Generator (Boiler)
29.3 Steam Engine
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Steam Power Plants
CAD Assignment on Steam Power Plants
Homework
Problems for Practice
30. Machine Tools
30.1 Introduction and Scope
30.2 Lathe
30.3 Shaper
30.4 Drilling Machine
30.5 Holding and Clamping Devices
Theory Questions
Viva-Voce Questions
Multiple Choice Questions
Assignment on Machine Tools
CAD Assignment on Machine Tools
Homework
Problems for Practice
Appendix 1 Some Useful Indian Standards
Appendix 2 Some Relevant Internet Sites
Appendix 3 List of Some Important AutoCAD Commands
Appendix 4 Various Tabs on the Ribbon and their Panels
Index

Citation preview

MACHINE DRAWING Includes AutoCAD Second Edition

About the Author Ajeet Singh graduated in Mechanical Engineering from Jodhpur University in 1963. While completing his masters degree in Heat and Power Engineering in 1970, he served as lecturer at Malviya Regional Engineering College, (which is now known as Malviya National Institute of Technology (MNIT) Jaipur. From 1970 onwards, he served at MNR Engineering College, which is now known as Motilal Nehru National Institute of Technology (MNNIT), Allahabad. He acquired a PhD degree from Allahabad University in 1979 while serving at MNNIT. As one of the most distinguished faculty members of his college, Dr Singh also served in various positions like President of Students’ Club, Dean: Academic, Dean: Research and Consultancy and lastly as Professor and Head of Mechanical Engineering Department from 1997. Besides being an academician, Dr Singh has also provided consulting services to many private and public companies like BHEL. He has published many research papers in national and international journals and has reviewed the journal of Institution of Engineers in the field of Automobiles and Tribology. He received the Railway Board prize for his paper on Fuel Injection. He is a fellow member of the Institution of Engineers, India, and Life Member of ISTE. Dr Singh has expertise in many programming languages and has wide experience in teaching CAD (Computer Aided Design) for many years. Experience in using computers, helped him write his previous book, Working with AutoCAD 2000, published by Tata McGraw Hill, which was widely accepted in India and abroad. He introduced the unique idea of combining machine drawing with newer methods of drafting using AutoCAD. His book Machine Drawing, which applied the techniques of AutoCAD 2005, was first published in 2007. The revised second edition emphasizes on AutoCAD 2010. Dr Singh also worked as Visiting Professor in foreign countries for 15 years. His final tenure, which lasted for 10 years, was at Salalah College of Technology, Salalah, Sultanate of Oman, where he completed his books on AutoCAD 2000 and the present book on Machine Drawing. After enjoying a fruitful and distinguished academic career for 44 years, and teaching at the undergraduate, postgraduate and doctoral levels, he now leads a retired life and spends his time reading, writing and travelling.

MACHINE DRAWING Includes AutoCAD Second Edition

Ajeet Singh Retired Professor and Head of Mechanical Engineering Department Motilal Nehru National Institute of Technology Allahabad

Tata McGraw Hill Education Private Limited NEW DELHI McGraw-Hill Offices New Delhi New York St Louis San Francisco Auckland Bogotá Caracas Kuala Lumpur Lisbon London Madrid Mexico City Milan Montreal San Juan Santiago Singapore Sydney Tokyo Toronto

Tata McGraw-Hill Published by the Tata McGraw-Hill Education Private Limited, 7 West Patel Nagar, New Delhi 110 008 Copyright © 2012 by Tata McGraw-Hill Education Private Limited. No part of this publication may be reproduced or distributed in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise or stored in a database or retrieval system without the prior written permission of the publishers. The program listings (if any) may be entered, stored and executed in a computer system, but they may not be reproduced for publication. This edition can be exported from India only by the publishers, Tata McGraw-Hill Education Private Limited. ISBN 13: 978-0-07-107294-6 ISBN 10: 0-07-107294-2 Vice President and Managing Director: Ajay Shukla Head–Higher Education Publishing and Marketing: Vibha Mahajan Manager—Publishing (SEM & Tech. Ed.): Shalini Jha Editorial Researcher: Harsha Singh Executive—Editorial Services: Sohini Mukherjee Sr. Manager—Production: Satinder S Baveja Production Executive: Anuj Kr Shriwastava Marketing Manager—Higher Ed: Vijay Sarathi General Manager—Production: Rajender P Ghansela Production Manager—Reji Kumar

Information contained in this work has been obtained by Tata McGraw-Hill, from sources believed to be reliable. However, neither Tata McGraw-Hill nor its authors guarantee the accuracy or completeness of any information published herein, and neither Tata McGraw-Hill nor its authors shall be responsible for any errors, omissions, or damages arising out of use of this information. This work is published with the understanding that Tata McGraw-Hill and its authors are supplying information but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought. Typeset at Script Makers, 19, A1-B, DDA Market, Paschim Vihar, New Delhi 110 063 and printed at Lalit Offset Printers, Jawahar Nagar Industrial Area, Loni Road, New Delhi 110 092. Cover Printer: SDR Printers RAXYCRLHDLDCQ

Dedicated to my wife, Mrs Kanwaljeet and Our grandchildren, Gaganjit, Karanjit, Ananya, Neha, Tanvi and Simar

Preface Any machine part which is produced is first designed and then its drawing is prepared. The industry then manufactures the part according to the details given in the drawing. Thus, drawing is the only means of communication between the design office and the manufacturing shop floors. Hence Engineering Drawing is quite an important communication tool for engineers. Engineering drawings were made manually in the past but now they are made with the help of computers, and are called Computer Aided Drafting (CAD). There are many good books in the market on engineering drawing but only a few of them cover CAD. Some books give CAD as only a single small chapter in the end, which does not help a student in correlating the art of drawing with CAD. There are some good books which focus solely on CAD. They describe the tools available in the software with a few examples. This book is written as a combination of both manual and computer methods which run in parallel, chapter by chapter. The idea is that a student who makes a drawing manually, should be able to create a similar drawing with the help of a computer. It will give a better understanding of the use of the software for engineering-drawing purposes. The examples selected for AutoCAD cover a majority of the relevant commands. The software is explained by showing actual toolbars and dialog boxes which appear on the screen to enhance the understanding of students. The software adopted in the first edition was AutoCAD 2005. The revised second edition describes AutoCAD 2010. For more details on the subject of AutoCAD, readers can consult the other book of the author, Working with AutoCAD 2000. This book not only gives elaborate drawings, but an effort has been made to describe all the basic knowledge required for each topic. The information given will be quite useful to answer questions asked in the viva-voce examinations. The contents of the book are selected to cover the syllabi of various universities/institutions offering machine drawing. Some chapters like Applied Geometry, Surface Developments, Intersections, Cams, Jigs and Fixtures, etc., are not given in the book but these chapters will be put on the Internet to make the book comprehensive. The chapters have been arranged in a logical order for step-by-step mastering of the subject. The book is suitable for first-year degree courses in Civil, Mechanical and Electrical Engineering and the second year of Mechanical Engineering courses. The production drawings section of the book on Tolerances, Limits, Fits, Geometric Tolerances and Surface Finish, etc., is very helpful for practicing engineers as well. Internet websites given in the Appendix makes the book useful for any person searching information on a topic concerning machine drawing.

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Preface

The conventions and terminology used in the book are mostly as per the Bureau of Indian Standards (BIS). But wherever there are different terms by BIS and AutoCAD, the terms of AutoCAD have been used so that students do not get confused while using the software. Explanations are accompanied by many pictorial drawings for better visualization of the concept. The author has had a long experience of 44 years of teaching this subject and is fully aware of the common mistakes which students commit. Therefore, these mistakes have been pointed out so that students do not repeat the same. The book has the following important features: ∑ The book has over 120 solved examples on manual drafting as well as on CAD to give a comprehensive idea to the students. ∑ Over 500 theory questions help students know as to what type of questions can be asked on the subject. They also help the teacher to select questions for setting examination papers. ∑ Multiple choice questions (totalling almost 400) are given at the end of each chapter for evaluating students quickly for short quizzes, etc. ∑ Fill up the blank questions have been so chosen that they check the key knowledge points of the chapter. ∑ Over 170 unsolved problems for practice are given to create a thorough grasp on the concepts of the drawing. They also form a good question bank for the teacher to set examination papers. Solutions of the unsolved problems have not been given intentionally, so that the students do not copy from the book without understanding. The contents of the book are divided into six sections: Section A The first chapter deals with the importance of drawing and Fundamentals of Drawing while the second chapter is on the general tools available in CAD. The initial settings, and the draw and modify commands are explained with the help of solved examples. The following chapters are on the materials and tools used for drawing, standard conventions for lines, lettering, and dimensions. Section B This is about Projection Methods. Various methods of projections like Orthographic, Isometric, Oblique, Perspective, etc., are explained to fully describe a 3D object on a 2D sheet. This helps to view an object from any side and to understand the methods of visualization. Section C This is about Joints and Couplings. Permanent joints like riveted and welded joints are described. Temporary joints formed by bolts/nuts, cotter, shaft couplings and pipe joints are also explained. CAD can be of help in copying a part in rectangular or polar array form. Use of this tool for copying many parts in an array is explained. How the drawings stored in a graphic library can be used in creating drawings for the joints and couplings are demonstrated here by examples. Sections A, B and C form the first course on Engineering Drawing for a majority of the universities/colleges and deal with all the disciplines of engineering. Section D This concentrates on Production drawings to be used in the shop floor. The mating parts have to be specified by a type of standard fit required for an application. It is not possible to manufacture any part of the exact dimensions put on the drawing and hence a certain amount of tolerance is also to be put in addition to the basic dimensions. The type of machine to be used for manufacturing is decided by the type of surface finish mentioned on the drawing. Geometric tolerances like squareness, flatness, etc., are sometimes specified on production drawings. Standard methods to specify materials and all this information is described in this section. How AutoCAD helps in putting these values very easily on the drawing is explained. This section and the next few sections are mainly for mechanical engineers and is given in the second course on machine drawing. This can be useful for practicing engineers as well. Section E This deals with Machine Parts like springs, belts and pulleys, bearings, and gears to transmit power. AutoLISP is a programming language to be used in AutoCAD. Fundamentals of this language are

Preface

ix

given to create parametric drawings. Once a program is made, it can be used to create a drawing by defining the values of the variable sizes. Section F This is on Part and Assembly Drawings. Machines are made by assembling different parts. How the parts are to be joined together are explained here. The main important parts of internal combustion engines, steam power plants are selected for these drawings. Some parts of the machine tools and hand tools have also been included. The drawings created as part drawings can be assembled very easily using AutoCAD to produce an assembly drawing. Appendix 1 contains some useful Indian Standards. Due to developing Internet facilities, useful websites for different topics are given in Appendix 2. Appendix 3 lists some commonly used AutoCAD commands. Appendix 4 shows the display of the icons of the various tabs of the ribbon. The online Learning Center of the book www.mhhe.com/singh/md2 provides a vast range of supplements. Instructors can take the advantage of the solution manual and Power Point Slides. Five chapters on Applied Geometry, Surface Developments, Intersections, Cams, Jigs and Fixtures not included in the book are also available at the above-mentioned site for the students as well as instructors. I am sure that the contents of the book will help readers in getting sufficient proficiency and knowledge on machine drawing and CAD for mechanical drawings. No human being is perfect. Errors and omissions are always possible from any one in spite of the best efforts. I hope the readers will agree with me and inform the publisher/author for improvements and corrections in the subsequent editions. Constructive suggestions for the improvement of the book are most welcome at my email address: [email protected]. Dr. Ajeet Singh January 2012

Acknowledgements The manuscript of the book and drawings were finalized at Salalah College of Technical (SCOT), Salalah, Sultanate of Oman. I am thankful to the Ministry of Manpower and the college administration for allowing me to use the computing facilities of the department in the course of preparing this book. I also thank the Director, Motilal Nehru National Institute of Technology, Allahabad, for creating an excellent academic and research environment and computing facilities in the college. I convey my gratitude to Dr R R Gaur, Professor of Mechanical Engineering, Indian Institute of Technology, Delhi, for his valuable suggestions during the preparation of the book. I convey my sincere thanks to my colleagues of SCOT for their suggestions while writing the AutoCAD part of the book. I would like to thank the editorial and production team of Tata McGraw Hill, who have been very cooperative and fast in communication even when they were located thousands of kilometers away. The book has undergone thorough reviews by many eminent academicians and their remarks have been very encouraging, mentioning the usefulness and uniqueness of the book. We would like to acknowledge them V K Jain Indian Institute of Technology (IIT) Kanpur, Uttar Pradesh Vinay S Marval Stani Memorial College of Engineering and Technology (SMCET), Jaipur, Rajasthan Harit K Raval Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat, Gujarat K Sankaranarayanasamy National Institute of Technology (NIT), Tiruchirappalli, Tamil Nadu R Sivasubramanian Coimbatore Institute of Technology, Coimbatore, Tamil Nadu G L Samuel Indian Institute of Technology (IIT) Madras, Tamil Nadu

Tarun Kanti Naskar Jadavpur University, Kolkata, Paschimbanga Darshak Raijiwala Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat, Gujarat T K Jana Haldia Institute of Technology, Haldia, Paschimbanga Umashankar Siddaganga Institute of Technology, Tumkur, Karnataka H Suresh Hebbar National Institute of Technology Karnataka (NITK) Surathkal, Karnataka

It will not be out of place to mention that I would not have been a professional and an author without the encouragement of my parents from my childhood. I thank my wife, Mrs. Kanwaljeet, for relieving me from the domestic duties to spare time for the book and bear my engagement in the book. Thanks are also due to my daughter Mrs. Maneet Kaur for the proof reading of the book and my daughters Mrs. Preety Singh and Mrs. Diljeet Kaur who inspired me to take up this work. Ajeet Singh

Contents Preface Acknowledgements

vii xi

PART A

1

DRAWING FUNDAMENTALS

1. Introduction to Drawing 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

What is a Drawing? 1 Uses of Drawings 1 Elements of Graphics 2 Methods of Expression 3 Methods of Size Description 3 Methods of Preparing Drawings 4 Types of Mechanical Drawings 4 Drawing Standards 7 Theory Questions 7 Viva-Voce Questions 7 Multiple Choice Questions 7

2. Computer Aided Drafting 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14

1

Introduction to Computer Aided Drafting 9 Advantages of Computer Aided Drafting 9 Starting the AutoCAD Program 9 AutoCAD Opening Screen 9 AutoCAD Commands 12 Function Key Assignments 12 Short-Cut Key Characters 12 UCS and UCSICON 13 Coordinate System 13 Units 14 Viewing a Drawing 14 Drawing Aids 15 Object Snap 15 Drawing Basic Entities 18

9

Contents

xiv 2.15 2.16 2.17 2.18 2.19 2.20 2.21

Correcting Mistakes 27 Object Selection 27 Modify Commands 28 Modify Properties 33 Match Properties 33 Pedit 34 Grips 34 Theory Questions 38 Viva-Voce Questions 39 Multiple Choice Questions 39 Problems for Practice 42

3. Drawing Apparatus 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15

44

Introduction to Drawing Equipment 44 Triangles 45 Ruler 45 Scales 46 Protractor 46 French Curves 46 Instrument Box 46 Stencils 47 Inking Pens 48 Drawing Sheet 49 Types of Paper 52 Drawing Sheet Fasteners 52 Pencils 53 Drawing Ink 54 Eraser 54

CAD 3.16 Equipment for Computer Aided Drafting (CAD) 54 3.17 Computer Software 56 Theory Questions 56 Viva-Voce Questions 56 Multiple Choice Questions 57

4. Lines and Freehand Sketching 4.1 4.2 4.3 4.4 4.5

Lines 59 Precedence of Lines 60 Thickness of a Line 60 Drawing Lines 60 Freehand Sketching 61

CAD 4.6 Lines Using CAD 64 4.7 Sketch Command 67 Theory Questions 69

59

Contents Viva-Voce Questions 69 Multiple Choice Questions 69 Assignment on Lines, Circles and Arcs Problems for Practice 71

5. Lettering 5.1 5.2 5.3 5.4 5.5 5.6 5.7

xv

70

72

Introduction 72 Guide Lines 72 Spacing between Lines 72 Width of Characters 72 Line Thickness of Letters 73 Spacing between Letters 74 Inclined Letters 74

CAD 5.8 5.9 5.10 5.11

Text Command 74 Mtext Command 77 Arc Aligned Text 77 Editing Text 77 Theory Questions 79 Viva-Voce Questions 80 Multiple Choice Questions 80 Assignment on Lettering 81 CAD Assignment on Lettering 81

6. Basic Dimensioning 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16

Introduction 82 Elements of Dimensioning 82 Dimensioning Circular Arcs 87 Dimensioning Diameters 87 Dimensioning Holes 87 Dimensioning Angles 88 Dimensioning Chamfers 89 Dimensioning Tapers 89 Dimensioning Undercuts 89 Dimensioning Repetitive Features 89 Dimensioning Equidistant Features 90 Dimensioning Threads 90 Dimensioning Curves 90 Dimensioning Methods 90 Placement of Dimensions 92 Sequence of Dimensioning 92

CAD 6.17 Layers 92 6.18 Dimensioning Commands 96 6.19 Dimensioning Methods 99

82

Contents

xvi

6.20 More Dimension Methods 102 Theory Questions 109 Viva-Voce Questions 109 Multiple Choice Questions 109 Assignment on Dimensioning 111 CAD Assignment on Dimensioning 111 Problems for Practice 112

PART B

METHODS OF PROJECTION

7. Orthographic Projections 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 7.14 7.15

113 113

Introduction 113 What is Projection? 113 Types of Views 113 Principle Picture Planes 115 Methods of Orthographic Projection 115 Hidden Details 117 Preliminary Decisions for Making a Drawing 118 Projecting Side Views 119 Projection of Straight Inclined Face 121 Projection of Circular Boundaries 121 Projection of Curved Boundaries 121 Understanding Orthographic Views (Blue Print Reading) 121 Missing Views 122 Some Drawing Conventions 123 Sequence of Drawing 123

CAD 7.16 Drawing Orthographic Views 127 7.17 Plotting 127 Thoery Questions 131 Viva-Voce Questions 132 Multiple Choice Questions 132 Assignement on Orthographic Views 133 CAD Assignment on Orthographic Views 134 Homework 134 Problems for Practice 135 Assignment on Missing Views 136 Problems for Practice 137

8. Sectional Views 8.1 8.2 8.3 8.4

Introduction 138 Types of Sections 138 Conventions in Sectioning 141 Section Lines (Hatching) 143

138

Contents

xvii

CAD 8.5 Hatching using AutoCAD 149 Theory Questions 151 Viva-Voce Questions 152 Multiple Choice Questions 152 Assignment 1 on Sectional Views 153 CAD Assignment on Sectional Views 154 Assignment on Half Sectional Views 155 CAD Assignment on Half Sectional Views 156 Problems for Practice 156 Difficult Problems for Practice 157

9. Auxiliary Views 9.1 9.2 9.3 9.4 9.5 9.6

161

Introduction 161 Types of Inclined Surfaces 161 Drawing Auxiliary View of an Inclined Surface 162 Drawing Auxiliary View of a Curved Surface 162 Illusions in Auxiliary Views 164 Skew Surfaces 164

CAD 9.7 Construction Lines 169 Theory Questions 171 Viva-Voce Questions 171 Multiple Choice Questions 171 Assignment on Auxiliary Views 172 CAD Assignment on Auxiliary Views 173 Problems for Practice 174

10. Axonometric Views and Oblique Views 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.12 10.13 10.14 10.15 10.16

Introduction 175 Types of Pictorial Views 175 Axonometric Views 176 Isometric Scale 177 Drawing Isometric Views 177 Projections of Non-Isometric Lines 178 Isometric View of Angles 179 Isometric Drawing of Circles 179 Isometric Drawing of Arcs 181 Isometric Drawing of Curved Objects 181 Isometric Sections 181 Dimensioning Isometric Drawings 182 Reversed Isometric 182 Dimetric Projections 182 Trimetric Projections 182 Oblique Projection 183

175

Contents

xviii 10.17 Drawing an Oblique View 183 10.18 Cabinet View 185

CAD 10.19 10.20 10.21 10.22 10.23 10.24

Isometric Grid 189 Isocircle 190 Viewports Command 190 Types of 3D Models 192 User Coordinate System (UCS) 193 Views 193 Theory Questions 197 Viva-Voce Questions 197 Multiple Choice Questions 198 Assignment on Isometric and Dimetric Views CAD Assignment on Isometric Views 200 Assignment on Oblique Views 201 CAD Assignment on Oblique Views 202 Homework 202 Problems For Practice 204

11. Perspective Views 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9

199

205

Introduction 205 Terminology 205 Factors Affecting Appearance 206 Selection of Parameters 206 Types of Perspective Views 208 Drawing a Perspective View 208 Perspective View of a Cylinder 211 Drawing a Perspective View of a Circle 211 Graticulation 213

CAD 11.10 Rays 217 11.11 Dview Command 217 Theory Questions 219 Viva-Voce Questions 219 Multiple Choice Questions 220 Assignment on Perspective Views 220 CAD Assignment on Perspective Views 221 Problems for Practice 222

PART C

JOINTS AND COUPLINGS

12. Riveted Joints 12.1 Introduction 223 12.2 Rivets 223 12.3 Making a Riveted Joint 224

223 223

Contents 12.4 12.5 12.6 12.7 12.8 12.9

xix

Classification of Riveted Joints 225 Joint Proportions 228 Applications of Riveted Joints 230 Structural Joints 230 Boiler Joints 234 Light Work Applications 236

CAD 12.10 12.11 12.12 12.13

Block 238 Creating a Block (Block Command) 238 Retrieving a Block (Insert Command) 239 Inserting a Block at Many Places (Minsert Command) 241 Theory Questions 242 Viva-Voce Questions 242 Multiple Choice Questions 242 Assignment on Riveted Joints 244 CAD Assignment On Riveted Joints 244 Homework 244 Problems for Practice 244

13. Threads 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9

245

Introduction 245 Terminology 245 Classification of Threads 247 Thread Profile 247 Pitch of Thread 249 Thread Designation 249 Specifications of Threads 251 Thread Representation 251 Internal Threads 253

CAD 13.10 Array Command 254 Theory Questions 258 Viva-Voce Questions 258 Multiple Choice Questions 258 Assignment on Screw Threads 259 CAD Assignment on Screw Threads 260 Homework 260 Problems For Practice 260

14. Bolts and Nuts 14.1 14.2 14.3 14.4 14.5

Introduction 261 Terminology 261 Bolt Proportions 261 Drawing a Bolt/Nut 262 Studs 264

261

Contents

xx 14.6 14.7 14.8 14.9 14.10 14.11

Screws 265 Locking Devices 266 Special Nuts 266 External Locking Devices 269 Spring Washers 270 Bolts and Nuts for Special Applications 270

CAD 14.12 Wblock Command 272 Theory Questions 274 Viva-Voce Questions 275 Multiple Choice Questions 275 Assignment 1 on Bolts and Nuts 276 Assignment 2 on Locking Devices 276 CAD Assignment on Bolts and Nuts 277 Homework 277 Problems for Practice 277

15. Welded Joints 15.1 15.2 15.3 15.4 15.5 15.6 15.7 15.8 15.9 15.10 15.11 15.12

278

Introduction 278 Types of Welding Processes 278 Types of Joints 279 Edge Preparation 279 Symbols 280 Specifying a Welded Joint 282 Fillet Welds 286 Groove Welds 287 Spot Welds 288 Seam Welds 289 Plug Welds 289 Surface Welding 290

CAD 15.13 Graphic Library 293 Theory Questions 294 Viva-Voce Questions 294 Multiple Choice Questions 294 Assignment on Welded Joints 295 CAD Assignment on Welded Joints 296 Homework 297 Problems for Practice 298

16. Shafts, Keys, Cotter and Pin Joints 16.1 16.2 16.3 16.4

Shafts 299 Keys 300 Types of Keys 301 Splines (IS 2327:1991, IS 3665:1990, IS 13088:1991) 304

299

Contents

xxi

16.5 Cotter Joints 305 16.6 Knuckle Joint 307

CAD 16.7 16.8 16.9 16.10 16.11

Solid Modeling 307 Solid Modeling Commands 309 Operations on 2D Objects to Convert to 3D Objects 310 Operations on 3D Solids 310 Composite Solids 313 Theory Questions 317 Viva-Voce Questions 317 Multiple Choice Questions 317 Assignment on Keys and Joints 319 CAD Assignment on Keys and Joints 319 Homework 319 Problems for Practice 319

17. Couplings and Clutches 17.1 17.2 17.3 17.4 17.5 17.6 17.7 17.8 17.9

320

Couplings 320 Muff Couplings 320 Rigid Flange Couplings 321 Flexible Couplings 323 Parallel Coupling (Oldham’s) 324 Universal Coupling 325 Constant Velocity Joint 326 Detachable Couplings 327 Slip Couplings 327

CAD 17.10 3 Darray 330 Theory Questions 333 Viva-Voce Questions 333 Multiple Choice Questions 334 Assignment on Couplings and Clutches 335 CAD Assignment on Couplings and Clutches 335 Homework 335

18. Pipe Joints 18.1 18.2 18.3 18.4 18.5 18.6 18.7 18.8 18.9

Pipes 336 Pipe Materials 336 Pipe Designation 336 Pipe Threads 337 Types of Pipe Joints 338 Joints for Cast Iron Pipes 339 Joints for Copper Pipes 340 Joints for Wrought Iron Pipes 340 Joints for Lead Pipes 341

336

Contents

xxii 18.10 18.11 18.12 18.13 18.14 18.15 18.16 18.17 18.18 18.19 18.20 18.21 18.22

Joints for Hydraulic Pipes 341 Union Joint 342 Expansion Joints 343 Pipe Fittings 344 Cast Iron Fittings 345 Flanged Fittings 346 PVC Fittings 348 Valves 348 Piping Symbols 350 Piping Layouts 352 Pipe Supports 353 Tubes 354 Tube Joints 355

CAD 18.23 Multilines (Mline Command) 355 18.24 Creating a New Mline Style (Mstyle Command) 356 Theory Questions 361 Viva-Voce Questions 361 Multiple Choice Questions 361 Assignment on Pipe Joints 362 CAD Assignment on Pipe Joints 363 Homework 363 Problems for Practice 364

PART D

PRODUCTION DRAWINGS

19. Tolerances, Limits and Fits 19.1 19.2 19.3 19.4 19.5 19.6 19.7 19.8 19.9 19.10 19.11 19.12 19.13 19.14

Introduction 365 Terminology 365 Tolerances and Manufacturing Processes 366 International Tolerance Grade (It Grade) 367 Fundamental Tolerances 369 Placing a Dimension with Tolerance 374 Cumulative Tolerances 374 Fits 379 Systems of Fits 379 Specifying a Fit 380 Types of Fits 380 Selection of Fits 381 Fits for Thread Fasteners 387 Gauges 387

CAD 19.15 Putting Tolerances using CAD 387 Theory Questions 390

365 365

Contents

xxiii

Viva-Voce Questions 391 Multiple Choice Questions 391 Assignment on Tolerances, Limits and Fits 392 CAD Assignment on Tolerances, Limits and Fits 393 Homework 393 Problems for Practice 394

20. Geometrical Tolerances and Surface Finish 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 20.10 20.11 20.12 20.13 20.14 20.15 20.16 20.17 20.18 20.19 20.20 20.21

395

Introduction 395 Types of Tolerances 395 Terminology 396 Frame 396 Datum 397 Material Condition 398 Tolerance Symbol 399 Tolerance Value 400 Indicating Geometrical Tolerances on Drawings 400 Form Tolerance for Single Features 400 Tolerances on Related Features 402 Run Out 405 Surface Texture 409 Profiles 410 Surface Roughness Number 410 Roughness Symbols 411 Lay 413 Roughness Grade Number and Grade Symbols 413 Roughness with Manufacturing Processes 414 Roughness for Typical Applications 415 Rules for Putting Roughness Symbols 416

CAD 20.22 Geometric Tolerances 418 Theory Questions 419 Viva-Voce Questions 419 Multiple Choice Questions 420 Assignment on Geometric Tolerances and Surface Roughness 421 CAD Assignment on Geometric Tolerances and Surface Roughness 422 Homework 422 Problems for Practice 423

21. Material Specifications 21.1 21.2 21.3 21.4 21.5 21.6

Introduction 425 Types of Engineering Materials 425 Ferrous Metals 426 Designation of Steels [IS 1762–1974 Part 1] 429 Steel Designation According to Chemical Composition [IS 7598–1974] 431 Code Designation for Ferrous Castings [IS 4863–1968] 433

425

Contents

xxiv 21.7 Non-Ferrous Metals 433 21.8 Plastics 437 21.9 Bill of Materials 439

CAD 21.10 Table Command 442 21.11 Block Attributes 443 Theory Questions 444 Viva-Voce Questions 444 Multiple Choice Questions 444

22. Production Drawings 22.1 22.2 22.3 22.4 22.5 22.6 22.7 22.8 22.9 22.10 22.11 22.12 22.13

Introduction 446 Title Block 446 Manufacturing Processes 447 Heat Treatment Processes 450 Tooling 451 Inspection 454 Jigs 454 Fixtures 455 Assembly Drawings 456 Standard Mechanical Components 457 Production Drawing 458 Process Sheet 458 Title Block 460 Theory Questions 461 Viva-Voce Questions 461 Multiple Choice Questions 462 Assignment on Production Drawings 463 CAD Assignment on Production Drawings 464 Problem for Practice 465

PART E

MACHINE PARTS

23. Springs 23.1 23.2 23.3 23.4 23.5 23.6

446

Introduction 466 Classification 466 Helical Spring 466 Leaf Spring 469 Conventional and Symbolic Representation of Springs 471 Diaphragm Spring 471

CAD 23.7 Helix Command 472 Theory Questions 475 Viva-Voce Questions 475 Multiple Choice Questions 475

466 466

Contents

xxv

Assignment on Springs 476 CAD Assignment on Springs 476 Homework 477 Problems for Practice 477

24. Belts and Pulleys 24.1 24.2 24.3 24.4 24.5 24.6 24.7 24.8

478

Introduction 478 Belts 478 Pulleys 480 Types of Pulleys 480 Flat Belt Pulleys 481 Grooved Pulleys 484 Toothed Pulley 485 Rope Pulley 486

CAD 24.9 24.10 24.11 24.12 24.13 24.14 24.15 24.16 24.17

Autolisp 487 Specifying Variables 490 Extracting Data from List Variable 491 Get Commnads 491 Mathematical Operations 491 Angles in Autolisp 492 Logical Operators 492 Conditional Branching (If Command) 492 Looping a Program 493 Theory Questions 495 Viva-Voce Questions 495 Multiple Choice Questions 496 Assignment on Belts and Pulleys 497 CAD Assignment on Belts and Pulleys 497 Homework 497

25. Bearings 25.1 25.2 25.3 25.4 25.5 25.6 25.7 25.8 25.9

Introduction 498 Classification of Bearings 498 Hydrodynamic Bearings 498 Plain Journal Bearing 499 Plain Journal Bearing Materials 499 Sleeve Bearing Supports 500 Hangers 503 Rolling Bearings 504 Mounting of Rolling Bearings 509

CAD 25.10 Managing Entities 510 Theory Questions 513 Viva-Voce Questions 514

498

Contents

xxvi

Multiple Choice Questions 514 Assignment on Bearings and Supports 515 CAD Assignment on Bearings and Supports 516 Homework 516 Problems for Practice 516

26. Gears 26.1 26.2 26.3 26.4 26.5 26.6 26.7 26.8 26.9 26.10 26.11 26.12 26.13 26.14 26.15

517

Introduction 517 Terminology 517 Types of Gears 518 Gear Tooth Calculations 519 Tooth Profiles 520 Base Circle 522 Drawing Approximate Involute Tooth Profile 523 Conventional Representation of Gear Teeth 525 Construction of Gears 525 Spur Gears 526 Helical Gears 527 Bevel Gears 528 Worm and Worm Wheel 529 Rack 531 CAD for Gear 532 Theory Questions 533 Viva-Voce Questions 534 Multiple Choice Questions 534 Assignment on Gears 535 CAD Assignment on Gears 535 Problems for Practice 536

PART F

MACHINES

537

27. Part and Assembly Drawings 27.1 27.2 27.3 27.4 27.5 27.6

Introduction 537 Detail Drawing 537 Assembly Drawings 540 Bill of Materials 542 Steps for Creating Assembly Drawings 544 Blue Print Reading 545 Theory Questions 549 Viva-Voce Questions 549 Multiple Choice Questions 550 Assignment on Part and Assembly Drawings 551 CAD Assignment on Part and Assembly Drawings 553 Homework 555 Problems for Practice 556

537

Contents

28. Internal Combustion Engines 28.1 28.2 28.3 28.4 28.5 28.6

xxvii

558

Introduction To I.C. Engines 558 Power System 558 Fuel System 577 Ignition System 582 Cooling System 583 Lubrication System 584 Multiple Choice Questions 586 Theory Questions 587 Viva-Voce Questions 587 Assignment on I.C. Engines 587 CAD Assignment on I.C. Engines 587 Homework 588 Problems for Practice 588

29. Steam Power Plants

590

29.1 Introduction 590 29.2 Steam Generator (Boiler) 590 29.3 Steam Engine 604 Theory Questions 615 Viva-Voce Questions 615 Multiple Choice Questions 616 Assignment on Steam Power Plants 616 CAD Assignment on Steam Power Plants 617 Homework 617 Problems for Practice 617

30. Machine Tools 30.1 30.2 30.3 30.4 30.5

618

Introduction and Scope 618 Lathe 618 Shaper 629 Drilling Machine 633 Holding and Clamping Devices 635 Theory Questions 640 Viva-Voce Questions 640 Multiple Choice Questions 640 Assignment on Machine Tools 641 CAD Assignment on Machine Tools 641 Homework 641 Problems for Practice 641

Appendix Appendix Appendix Appendix Index

1 2 3 4

Some Useful Indian Standards Some Relevant Internet Sites List of Some Important AutoCAD Commands Various Tabs on the Ribbon and their Panels

642 643 644 648 650

Part A

1 1.1

DRAWING FUNDAMENTALS

Introduction to Drawing

WHAT IS A DRAWING?

All school education is in word language. One has to learn it to read, write and speak. In word language, to describe an object for its shape and size, one has to use many sentences for its complete description. Large vocabulary is required to express complete description for communication. The problem is of a higher order when communication is to be done between two persons knowing different languages. For such cases, interpreters who know both the languages are needed to translate. Thus, word language is quite cumbersome, if one tries to use it universally where languages are in dozens. Drawing is a graphic language that can be used to express precisely the shape and size of an object in a compact form without having much vocabulary. Such an expression will be independent of the country and can be understood universally even by illiterate persons to some extent. For example, any illiterate person can identify a chair if he sees its pictorial drawing (Fig. 1.1). An educated person will be able to tell its dimensions mentioned on the drawing. Perhaps one page description will Fig. 1.1 A Chair be needed if it has to be described in words. Thus drawing is a silent and compact language through which one can communicate to deaf and dumb individuals as well. Graphic language has the following advantages over word language while describing an object: 1. It is independent of any regions language. 2. It offers compact description. 3. It is a silent language and can be used by even the deaf and the dumb. 4. It gives a clear picture in the mind quickly. 5. Even illiterate persons can follow it to some extent. 6. Complicated machines can be described by different drawings for each part and then an assembly drawing can be made showing the relative position of the different parts.

1.2

USES OF DRAWINGS

In addition to describing an object, drawings can be used for the following important communications. See Fig. 1.2. It can be used for mathematical conversions in the form of nomograms. For example, to convert degree Centigrade to degree Fahrenheit (Fig. 1.2A).

Part A – Chapter 1

2

Dependence of (x, y) variables can be shown graphically by plotting X, Y graphs. For example, a P-V diagram for an engine (Fig. 1.2B). PI charts can be used to show the percentage of different elements (Fig. 1.2C). Bar charts Electrical/electronics circuitry is drawn showing the various connections of different components (Fig.1.2E). Structures are shown by structural drawings. Designs of buildings are shown by architectural drawings. Surveyors use drawings for maps and topography. Discussion in this book is limited to only the drawing of mechanical engineering components and machines.

Fig. 1.2

1.3

Various Applications of Drawings

ELEMENTS OF GRAPHICS

Drawings are made with lines and arcs. Each line reprecurved objects. Lines are connected according to geometry to represent planes and ultimately the shape of the object. for size. Figure 1.3 shows the drawing of an object for its shape and size. Lines and curves represent its shape and the numbers mentioned are the dimensions in mm. When the it completely.

Fig. 1.3

Graphical Representation of an Object for Shape and Size

Introduction to Drawing

1.4

3

METHODS OF EXPRESSION

An object can be expressed by drawing in many ways. One must select the best-suited method to describe the shape. The object can be drawn of the same size if it can be accommodated on the paper. If it is bigger than the paper size, then it has to be reduced and if it is very small, it can be enlarged suitably for easy readability. Two methods of representations used are: (a) Pictorial representation (b) Orthographic projections Pictorial representation is a view which is seen from an angle such that its three faces are visible. Figure 1.4(A) represents a pictorial view of a V block. A pictorial view can be isometric, oblique or perspective. These views are described in detail in Chapters 10 ad 11.

(A) Pictorial view

(B) Orthographic projections

Fig. 1.4 A ‘V’ Block

Fig. 1.5 A Sectional View

A majority of engineering drawings use orthographic method of representation. Orthographic views of the block V are shown in Fig. 1.4(B). In this method, the object is placed in such a way that the most representative face is on the front side. The Front view is then drawn while viewing from front. Then what is visible from the top is drawn, and is called the Top view or Plan. Side view is drawn by viewing from either the left or right side, whichever is more informative. Thus generally there are objects, even one view may be enough to describe the shape. These views are discussed in detail in Chapter 7. Sometimes sectional views are also drawn to show the internal details, which otherwise would have not been possible in outside views (Chapter 8). Figure 1.5 shows a sectional view of a hollow part. Hatching lines are drawn in the area where the material is cut by the sectioning or cutting plane.

1.5

METHODS OF SIZE DESCRIPTION

tion for making a complete drawing. Size is given by dimensions for linear distances, radii, diameters, angles, etc. Dimensions given are the actual dimensions of the object and not the scaled dimensions for scaled views. In production drawings, even tolerances are given (Refer Chapters 19 and 22 for more details). These are the maximum possible manufacturing errors that can be tolerated on each dimension. Figure 1.6 shows dimensions with and without tolerances. Units used are mm or metres depending upon the size of the object.

Part A – Chapter 1

4

(A) Dimensions without tolerances

(B) Dimensions wih tolerances

Fig. 1.6 Specifying Dimensions of Object

1.6

METHODS OF PREPARING DRAWINGS

Drawings can be prepared in three different ways:

1.6.1

Freehand Sketching

Sketching is done with pencil and paper without any aid of drawing apparatus. It is good in learning process and for preliminary drawings. Lines may not be of the exact length in such a drawing. Once the idea expressed

1.6.2

Finished Drawings

These drawings are drawn with pencil or ink on paper or special drawing material with the aid of drawing apparatus for good draftsmanship. Straight lines are drawn with T-square or a drafter or set squares (discussed in Chapter 3). Circles and arcs are drawn with compass and angles with protractor. Letters are written using stencils for good presentation. Special apparatus are also used at times to draw curves. The appearance of the drawing depends upon the skill of the draftsman.

1.6.3 Computer Aided Drafting (CAD) This is the latest method of drawing. The drawing is drawn on the screen of the computer using softwares like AutoCAD, CADKEY, etc. Editing becomes quite easy in such drawings. Finally the drawing is saved help of a plotter. Small drawings up to A4 size can be printed by a printer. Large and colored drawings are possible with multipen plotters or by changing pens on a single pen plotter. The quality of such drawings is excellent and does not depend upon the skill of the person. Basics of AutoCAD software are described in Chapter 2.

1.7 1.7.1

TYPES OF MECHANICAL DRAWINGS Machine Drawings

Drawings of machine elements are called machine drawings. They are generally represented with views from different sides like Front view, Top view and Side view. Figure 7. S1 in Chapter 7 shows machine drawing of an object. Dimensions on the views indicate the size.

Introduction to Drawing

1.7.2

5

Production Drawings

These drawings are also machine drawings but in addition to dimensions, they furnish tolerances, geometChapters 19 and 22 for details. Geometric tolerances

Ø7.9–8.1 Ø0.12 M A C M

45°

Ø0.08 M B M

Ø0.06 M A

0.05 A 0.12 A C

57.2 56.9

B

88 Ø 87. .2 9

44.2 43.9

10 Ø9 0.2 9.9

C

Ø 51 50 2 ,9

0.1 B

10.2 9.9

0.02 A 31.67 31.37 41.2 40.9

57.2 56.9 Side view

Ø 32.00–32.13.[32H11]

8

Tolerances

Sectional front view

Fig. 1.7 A Production Drawing

1.7.3

Assembly Drawings

A machine consists of many parts. Drawing showing the position of each part with respect to each other is

1.7.4

Sub-Assembly Drawings

When a machine is big and has a large number of parts, e.g. a car, it may have sub assemblies like engine, clutch, gearbox, etc. An assembly drawing is an assembly of such sub-assembly drawings.

1.7.5

Exploded Drawings

These drawings give the pictorial views of each component of an assembly and they are arranged in the same sequence in which they are to be assembled. Figure 1.8 is an exploded view with part number for an air compressor.

Part A – Chapter 1

6

Fig. 1.8 Exploded Drawing of an Air Compressor

1.7.6

Part Drawings

Detailed drawing of each part of a machine is called a part drawing. Production drawing of a part is also called a part drawing or working drawing.

1.7.7

Installation Drawings

These drawings are supplied by the manufacturers to the client giving the overall and all dimensions of the assembly which may be needed during installation. For example, details of foundation holes.

1.7.8

Tabular Drawings

These drawings are used for parts that have same shape but different dimensions. In that case, the drawing can be dimensioned with sizes as A, B, C, D, etc. and the values of A, B, C and D can be tabulated in a table. Figure 1.9 shows a tabular drawing of a washer.

Fig. 1.9

A Tabular Drawing

Introduction to Drawing

1.7.9

7

Patent Drawings

These drawings are used to get a patent of a machine. The drawing could be in orthographic view (Chapter 7) or in pictorial view (Chapters 10 and 11).

1.8

DRAWING STANDARDS

Machine drawing is used to communicate information to industries. To have uniformity in drawings they are required to follow some drawing standard approved by International Standards Organization (ISO). In India, Bureau of Indian Standards (BIS) has been assigned the job of standardizing the items for interchangeability of parts. Standards are available for any machine component as well as for the drawand was formulated in1960. It was revised in 1972. The latest revision was in1988 which is numbered as SP-46. All advanced countries have their own standards. Conventions followed in this book are as per Indian Standards. American National Standards Institute (ANSI) also has standards for drawings.

THEORY QUESTIONS 1. 2. 3. 4. 5. 6.

What are the advantages of graphic language over word language? What are the various types of representations that can be made using drawings? Give two important methods of representing a component. What are the various types of machine drawings? What is meant by an installation drawing? What do you mean by an exploded view?

VIVA-VOCE QUESTIONS 1. Differentiate between an assembly, sub-assembly and part drawing. 2. What is a tabular drawing? Where is it used? Explain with an example. 3. What is the importance of following Drawing Standards?

MULTIPLE CHOICE QUESTIONS Tick the correct answer: 1. Working drawing is used by (a) general public (c) salesman 2. Installation drawing is required by (a) purchase department (c) sales engineer 3. Bar chart is used to (a) give stock position of bars (c) length of bar

(b) designer (d) manufacturing industry (b) customer (d) production engineer (b) cross-section of steel bars (d) display data

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4. Pi chart is used for (a) converting circumference into diameter (b) evaluating value of Pi (c) displaying percentage of parametric elements (d) none of the above 5. A drawing giving details about size tolerance, heat treatment, etc. is known as (a) production drawing (b) assembly drawing (c) exploded drawing (d) machine drawing 6. The abbreviation CAD stands for (a) Common Application Data (b) Cancel All Drawings (c) Computer Aided Drafting (d) Call A Design 7. The work of standardization in India is done by (a) Government of India (b) National Institutes (c) Indian Institutes of Technology (d) Bureau of Indian Standards 8. The latest number of Indian Standard for Drawing is (a) SP-46 (b) IS 696 (c) ISO 235 (d) ISD 011 9. Tabular drawing is used where parts have (a) rectangular shape (b) same shape and size (c) same shape but sizes are different (d) same size but different shape

ANSWERS 1. (d) 7. (d)

2. (b) 8. (a)

TO

3. (d) 9. (c)

MULTIPLE CHOICE QUESTIONS 4. (c)

5. (a)

6. (c)

2 2.1

INTRODUCTION TO COMPUTER AIDED DRAFTING

Computer Aided Drafting (CAD) is becoming a powerful drawing tool even on personal computers now. Many softwares are available for drafting but the most versatile and commonly used software is AutoCAD. It is quite exhaustive and is internationally known for drafting purposes. AutoCAD has been developed in stages. The version AutoCAD 2010 is being described in this book. The minimum requirement for installing CAD is an 80-GB (or more ) Hard disk, a CD-ROM drive, a true color monitor, 512 MB RAM, a 2 or 3 button mouse, a printer or a plotter.

2.2 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

2.3

ADVANTAGES OF COMPUTER AIDED DRAFTING Feasibility of compact storage in a pen drive or hard disk. Drawings can be scaled up or down with ease without redrawing. Excellent drawing quality independent of the skill of the user. Editing can be done easily. Colored drawings are possible using multi-pen plotters. Line thickness, type of line and color can be set and constantly maintained. Neat output even without drawing instruments or drafting skills. Commonly used components can be pre-stored in a graphic library. Many hatch patterns are available that can be used wherever desired. Rectangular or polar arrays can be created easily. Dimensioning is very easy as extension lines, dimension lines, arrows and dimension values are put automatically. A multi-layer drawing can be created. Each layer acts like a transparency. Three-dimensional drawings can be seen from any viewpoint for better visualization. Information about length, area, perimeter, volume and mass, etc., is easily calculated. Programmable drawings are possible using AutoLISP or C languages.

STARTING THE AUTOCAD PROGRAM

It is presumed in this book that AutoCAD software is installed on the computer and the user has a basic knowledge of computers. Click the AutoCAD icon on the desktop or click the START button at the lower left corner of the screen, followed by the sequence of selections given below: START

2.4

Programs

Autodesk

AutoCAD 2010

AutoCAD 2010

AUTOCAD OPENING SCREEN

The opening main screen of AutoCAD is shown in Fig. 2.1. This screen has the following items from top to bottom:

10

Part A – Chapter 2

Fig. 2.1 Opening Screen of AutoCAD 2010

(a) Logo of AutoCAD is located on the left upper corner. (b) Icons present. A default File name [Drawing4.dwg] in this sequence as shown below:

(c) The Menu bar displays options like File, Edit, View, etc., as shown below: If this is not visible, you can type the system variable Menubar at the command line and set its value as 1 to display. A zero value hides this bar. (d) The Ribbon has eight tabs like Home, Insert, etc., as shown below: On the extreme right, a small triangle pointing downwards controls the display of the ribbon. A click on to the options shown below. The options will change depending upon the selection of the tab on the ribbon.

Computer Aided Drafting

11

The second click closes the ribbon completely and the third click reopens the ribbon. If the ribbon is not visible, it can be displayed by typing the RIBBON command at the command line. The RIBBONCLOSE command closes the ribbon window. By default the ribbon displays the Home tab which has eight panels like Draw, Modify, etc., as shown in Fig. 2.1. Display of all the tabs is shown in Appendix 4.

(e) (f) (g) (h)

(i)

A panel has a set of icons related to that menu option. Each panel can be further extended by clicking the arrow pointing downwards at the bottom of each panel. The display of the ribbon varies with the tab selected on the bar. By default it is at the Home Tab. Some icons have a small downward arrow on the side. Clicking this triangle displays all the options available for that command. Display of panels can be controlled by right clicking on the ribbon. A popup dialog box appears to control tabs or panels. Click on panels and then choose the panel which you want to display. One click sets it ON while the second click sets it OFF. It is good to remember the shape of each icon. However, if you forget, just bring the mouse over the icon for a while and a tool tip is displayed showing the job assigned to that icon. . The Drawing area is the major central area of the screen on which a drawing is created. A cross hair is displayed in this area. When the mouse is moved, this cross hair moves over the screen. The UCS icon is located at the lower left corner of the drawing area. It displays two arrows showing positive directions of X and Y. The Z direction is towards the user from the screen. The Layout line is at the bottom of the screen below the drawing area. You can select a layout here. The default is Model Layout. The Command line is just below the Layout line. See Fig. 2.1 where “Command” is written. The commands are typed in this area. You must always see this area. All the prompts for the data required are displayed here. Read the prompt, type the data as asked for and then press the Enter key ( ). The Status line is at the bottom-most part of the screen. On the left-hand corner, it displays X, Y and Z coordinates of the intersection point of the cross hair lines. After that it displays many icons such as SNAP, GRID, ORTHO, etc, which are labeled in Fig. 2.2. Select any one by clicking over it. The button is shown pressed when active.

Fig. 2.2 Meaning of the Icons on the Status Bar of AutoCAD 2010

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The display of icons on the status line can be controlled by clicking Application status bar icon (3rd from right side in Fig. 2.2) on the status line. A box with many check boxes appears. Check the icons which are required. Clicking the Clean screen icon on this bar (2nd from the last) clears all the menus and a full screen is made available for drawing. The last icon on the status line can be used to adjust the size of the opening screen, by pointing it and dragging to increase or decrease the size. The other icons are described in Section 2.12 and wherever required.

2.5

AUTOCAD COMMANDS

Commands are used to do an activity, for example, to draw a line use LINE command. First, open a new or (a) Click on an icon of the ribbon with the left mouse button. (b) Click an option on Menu bar. From the popup menu, select a choice by clicking the mouse on it. (c) At the Command line type a command using the keyboard and then press Enter ( ) key. Note: left mouse button. If you can remember the shape of icons If the same prompt repeats, press Enter to quit. Right mouse button can also work as Enter key. By pressing only Enter at the command prompt, the previously used command is automatically activated.

2.6 F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11

2.7

FUNCTION KEY ASSIGNMENTS Displays Help Toggles between the text and graphics screen Running Object Snap on/off Tablet (an input device) on/off Switches between the top, front and side views for isometric drawings Switches dynamic UCS to On or Off Grid on/off Ortho on/off; if ON, lines are either horizontal or vertical Snap mode on/off Polar option on/off Object Snap Tracking on/off

SHORT-CUT KEY CHARACTERS -

Computer Aided Drafting Table 2.1 Short-cut Key

2.8

Command name

13

Commands and their short-cut keys Function

A

ARC

Draws an arc

C

CIRCLE

Draws a circle

E

ERASE

Deletes the selected object(s)

F

FILLET

Creates a radius at the intersecting lines

G

HATCH

Displays Boundary Hatch and Fill dialog box

L

LINE

Draws a line

M

MOVE

Moves a drawing from one place to another but drawing coordinates change

O

OFFSET

P

PAN

Moves drawing on screen without changing its coordinates

R

REDRAW

Redraws the whole drawing

S

STRETCH

T

TEXT

Writes text

V

VIEW

Displays View dialog box

W

WBLOCK

Displays Write Block dialog box

X

EXPLODE

Breaks a group of entities into separate entities

Z

ZOOM

Enlarges or reduces the view

UCS AND UCSICON

AutoCAD uses 3-dimensional coordinate system. The X and the Y coordinate system is called the World Coordinate System, or in short, WCS. Its icon is shown at the lower left corner in the drawing area showing directions of the X and Y axes by arrows and a small square at the intersection (Fig. 2.1). The Z direction is taken at right angles to the screen and outwards. There is another coordinate system called the User Coordinate System display can be put On or Off or the position prompts for options. The option between conical brackets < > is the default option. Command: UCSICON Enter an option[ON/OFF/All/No origin/Origin/Properties]:

The position and orientation UCS command. Select any one option by typing a character written in uppercase for the option on the prompt line given below. Command: UCS Enter an option [New/Move/orthoGraphic/Prev/Restore/Save/Del/Apply/?/World]: :

2.9

COORDINATE SYSTEM

The lower left corner of the screen is taken as the origin and is shown by the location of WCS. Positive X is on the right-hand side of the origin and the positive Y is vertically upwards. Relative coordinates with respect

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AutoCAD accepts coordinates in any of the systems given below with the following syntax: Cartesian Relative Cartesian Polar Relative polar coordinate

X, Y, Z measured from the origin. x, y, z (x, y and z L< , Z (L is the distance from origin and Z is the height). L‘< , Z’ (L’ and

is the angle from the X axis and

are relative distance and angle from X axis and Z’ is

Spherical coordinate

L < < (where is the angle in a vertical plane) AutoCAD accepts coordinates in three dimensions. If only X and Y values are given, it assigns zero value to the Z coordinate automatically. The co-ordinates can be given by typing values for the coordinates from the keyboard or by clicking the left mouse button at the location of the point.

2.10

UNITS

Command: UN

The Drawing Units dialog box is displayed. The upper left corner displays the Length tile. In this tile, click the arrow in the combo box and select a Type and Fractions. Similarly, for Angle Decimal Degree is most common. Precision is the number of digits after decimal point to appear with the dimension, e.g., 15.1 or 15.13. In the Precision angle units. Select appropriate units in combo box. The effect of this setting is displayed in the Sample Output tile at the bottom of the dialog box. The direction from where all the angles are measured is set by clicking the Direction button at the bottom of the dialog box. The Direction control dialog box is displayed. East direction means horizontal direction. Click on any one of the radio buttons as desired and then click the OK Click the OK button to save and exit.

2.11

VIEWING A DRAWING

The ZOOM command is used to enlarge or reduce the viewing size of a drawing. ZOOM, PAN and VIEW commands can be used even when another command is in progress. Type Zoom or only Z at the command line and press Enter key. Command: ZOOM [All/Center/Dynamic/Extents/Previous/Scale/Window/Object] :

of the option and pressing Enter key. All Window option displays only the drawing which is selected by clicking the mouse on two diagonal corners of the window on the screen. PAN command is used to move the window around the drawing and the coordinates of the objects remain unchanged. In MOVE

Computer Aided Drafting

2.12

15

DRAWING AIDS

These aids are available on Status line (See Fig. 2.2). The following commands help in creating a drawing.

2.12.1

Grid

tion. The grid can also be rotated. The grid points do not appear while plotting the drawing. A grid can be activated by clicking the GRID button at the bottom of the screen on Status bar or by pressing Function key F7. A function key is a toggle key. Pressing once puts the grid on, and the second pressing puts it off. The following are the options of this command: Command: GRID Specify grid spacing (X) or [ON/OFF/Snap/Aspect] :

Specify a value of grid spacing

2.12.2

Snap

Snap is the smallest invisible distance of increment that can be set for the mouse. If snap is set ON, the mouse moves in steps of the set increment. To select any intermediate point between the dots of the grid, put snap Off by pressing F9 or on Status line click the SNAP button or type the command as under: Command: SNAP Specify snap spacing or [ON/OFF/Aspect/Rotate/Style/Type] :

Specify snap increment or put it off

2.12.3

Ortho

Ortho is short form of Orthogonal and it means 90° to each other. If this mode is set on, all lines are drawn only along the X and Y directions. On Status bar, click on ORTHO button to put it On or Off or press F8 Function key or type the command at command line as under: Command: ORTHO Enter mode [ON/OFF] :

2.13

Type an option: On or Off as desired.

OBJECT SNAP

Object Snap is also called OSNAP in short. Picking a point exactly and quickly with the mouse is quite difdialog box shown in Fig. 2.3. It can be displayed by OSNAP command. Figure 2.3 shows the various object snaps and the symbol for each snap which appears on the entity while selecting. For example, a rectangle is for the end point, a triangle for the midpoint etc. Click on the check box whichever is required frequently as shown by green arrow in Fig. 2.3. To disable object snap use F3 key. Pressing F3 again enables it again. Osnap button on task bar can also be used for this purpose. It can also be displayed by DDRMODES and press Enter key. Command: DDRMODES

Drafting setting dialog box is displayed. Click the tab for Object Snap and select an option.

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Fig. 2.3

Drafting Settings Dialog Box

Example 1 Draw a rectangle of size 100 80 mm and then draw its center lines, diagonals etc. as shown Example 1. This example demonstrates the following: Grid and Snap

Solution 1. START

Programs

Autodesk AutoCAD 2010 AutoCAD 2010 File on Menu bar and choose acadiso Template. Click OK button. Or type a command QNEW at command line and press Enter key. 3. At the command prompt, type Limits and press Enter to set the drawing limits as 297, 210 for A4 size sheet. Only the text shown in bold is to be typed by the user. The symbol ‘ ‘ represents Enter key. Command: LIMITS Specify lower left corner or [ON/OFF] : Specify upper right corner : 297,210

4. At the command prompt, type UNITS and press Enter. Drawing Units dialog box is displayed. In the Length tile, click the arrow in the combo box and choose Decimal as Type and Precision as 0.0. Choose the Type and precision in the Angle tile also as decimal degrees Drop scale combo box select millimeter. Click the OK button.

Computer Aided Drafting

Fig. 2.S1

17

Example on Use of Grid and Snap

Command: GRID Specify grid spacing(X) or [ON/OFF/Snap/Aspect] : 10 The grid should now be visible. If not, then press Enter to activate the previous command and type ON and press Enter or press F7. 6. At the command prompt, type SNAP and press Enter to set snap spacing. Command: SNAP Specify snap spacing or [ON/OFF/Aspect/Rotate/Style/Type] : 10 Check that Snap button of the status bar at the bottom is highlighted. If not, press F9. You can also use the Snap command and type “On” and press Enter. Command: LINE Click on a grid point on lower left corner Specify next point or [Undo]: Click on 10 grid points on right Specify next point or [Undo]: Click on 8 grid points above Specify next point or [Close/Undo]: Click on10 grid point on left Specify next point or [Close/Undo]: C Type C to close the lines LINE command again and make the inner rhombus. When all the four lines are drawn, press Enter two times to quit from the line command. Repeat the same command for diagonals and center lines. 9. On Menu bar, click File. From the pull-down menu choose Save or Save As option. In the Save as selection, many options for the versions are displayed such as AutoCAD R2004 or R2007, etc. Choose a version by clicking over it. Type the name at the command line at the bottom, e.g., Example 1 and press Enter key. Alternately use QSAVE command to save it in the default version of R2010.

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2.14

DRAWING BASIC ENTITIES

In AutoCAD, the screen acts as an imaginary drawing sheet. Each drawing is created using entities like lines,

feed the required data. If the prompt repeats, and you want to quit, press Esc key. To create an entity, use any one of the following methods: On Home option of the ribbon, click an entity on the Draw panel (Fig. 2.4).

Fig. 2.4 Draw Panel of the Ribbon in Extended Condition

Fig. 2.5

Meaning of the Icons of the Draw Panel

If the icon of the entity is not visible, click the arrow at the bottom of panel to display more icons. The various icons are labeled in Fig. 2.5. On Menu bar, click Draw and from the popup menu choose an entity, or On Command line, type the command for the entity and press Enter

2.14.1

Multiple Points

Point is used to mark a center of an arc or a circle. AutoCAD offers 20 styles of points and they can be set using Pdmode system variable at the command prompt. Size of the point can be changed and set by the system variable Pdsize. Both the point style and size can be changed by a single command DDPTYPE. This

Computer Aided Drafting

19

command displays Point Style dialog box. Click the type of the point required. The size of a point can be entered in absolute units or a percentage of the screen size. The command name is POINT. Go on clicking at

2.14.2

Line

AutoCAD offers many types of lines as named below: Line A simple straight continuous line Polyline A wide solid/hollow, parallel/taper line 3D polyline A line of segment of lines or arcs in space. It can can be non-coplaner Spline A curved line Multiline option of the menu bar. Construction line Ray To draw a continuous straight line, On Draw panel of the ribbon, click on Line icon or On Menu bar, click the Draw option and select line from the popup menu, or On Command line, type the command LINE or L and press Enter. Command: L Specify a point by mouse or type coordinates through keyboard NOTE: The text written above is bold letters is to be typed by the user. The text in italic letters is mentioned as guidance to the user for that prompt. coordinates of the starting point of the line either by clicking the mouse at the required location or by entering value of (x1, y1) co-ordinates. Then enter the location of the other end of the line (x2, y2) through keyboard x3, y3), (x4, y4), etc. and Enter to end the command. If you want to draw the last line up to the starting point, i.e. (x1, y1), type C to close the polygon made by the lines. After every entry of coordinates at the prompt, do not forget to press Enter key ( ). Example 2 (after Section 2.14) demonstrates the use of the commands. Coordinates can be given in any of the following forms: Absolute Cartesian coordinates, X, Y and Z or only X,Y if Z only the length of line segment. It will be taken in the direction in which the mouse is placed relative to the previous point. To draw only horizontal or vertical lines, you can put ORTHO setting ON by clicking ORTHO button on the status line or by pressing F8 key. You can enter only length. A simple line can be dashed, center line, etc. At the command prompt, type DDLTYPE and press Enter to load different types of lines. Linetype Manager dialog box is displayed. Click on Load… button. Load or Reload Line types dialog box is displayed. Scroll the various line types displayed and choose a line type, e.g. ‘Center’. To choose more than one line type press Ctrl key and then choose another line. Click OK on both the dialog boxes. The Modify command can modify an existing linetype. On the menu bar, click Modify and then on the popup menu, click on Properties and select the line to be changed. Then click on the desired type of line.

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2.14.3

Circle

To draw a circle, On Menu bar, click Draw and then choose Circle from the Popup menu, or On the Draw panel of the ribbon, click the Circle icon shown above or click the arrow on its side to displays all the options of the CIRCLE command as shown in Fig. 2.6, or On Command line, type the command CIRCLE or only C and press Enter. The prompt sequence is: Command: C Specify center point for circle or [3P/2P/Ttr (tan tan radius)]:

The Circle command offers six options. The default option is Center point

Fig. 2.6

Options of the CIRCLE Command

The meaning of each is given below: 3P 2P A circle passing through 2 points of a diameter. Ttr The other two (Tan Tan Tan) and (Center and diameter) are not shown in the options but can be seen in the popup menu or from the type 3P and press Enter key. Then specify coordinates of each point as prompted on the command line.

2.14.4

Arc

The Arc command creates an arc from any from the following list: Start point Center point End point Radius Included angle Chord length Direction at start point. Specify the value asked at the prompt or type the character/s displayed in uppercase to specify other value within [ ] and press Enter key. For example, type CE for specifying [CEnter]. To draw an arc, On Menu bar, click Draw, and then from the popup menu click Arc or On Draw panel of the ribbon, click the Arc icon shown above or click arrow on its right to see all the 11 options (Fig. 2.7), or On Command line, type the command ARC or A and press Enter Fig. 2.7

Options for the Arc

Computer Aided Drafting

21

The prompt sequence is as under: Command: ARC Specify start point of arc or [CEnter]: Specify second point of arc or [CEnter/End]: Specify center point of arc: Specify end point of arc or [Angle/chord Length]:

2.14.5

Rectangle

Drawing four lines using a LINE command can make a rectangle but the RECTANG command can make it by specifying any two diagonal corners. To draw a rectangle, On Menu bar, click Draw, and then from the popup menu click Rectangle, or On Draw panel of the ribbon, click the Rectangle icon shown above, or On Command line, type the command RECTANG and press Enter. The prompt sequence is as under: Command: RECTANG x1,y1 Specify other corner point: x3, y3

(x1, y1) are the coordinates of one corner and (x3, y3) coordinates of the diagonal corner. This command offers many other options within [ ] as described below. Type the uppercase character of the option and press Enter: Chamfer Creates a rectangle for which each corner is chamfered. First type C to specify the chamfer distances and then specify the imaginary extended diagonal corners. Elevation Creates a rectangle not at z Fillet the imaginary extended diagonal corners. Thickness Width

2.14.6

Polygon

A polygon of any number of equal sides can be created by the POLYGON command. On Menu bar, click Draw, and then from the popup menu click Polygon, or On Draw panel of the ribbon, click the Polygon icon shown above, or On Command line, type the command POLYGON and press Enter The prompt sequence is as under: Command: POLYGON Enter number of sides : Specify center of polygon or [Edge]: Enter an option [Inscribed in circle/Circumscribe] Specify radius of circle:

two options Center and Edge as explained below:

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22

A. Center Option Specify the center of a circle. This circle is not visible and is an imaginary circle on which a polygon is drawn. Inscribed option draws polygon inside the circle or Circumscribed option draws polygon outside the circle. Type I for Inscribed or C for Circumscribed.

B. Edge Option Do not specify center of polygon at the second prompt but type E for Edge option and press Enter key. After

Specify second end point of edge:

Specify coordinates for point 1 and point 2 of an edge. A polygon is drawn in the direction from point 1 to point 2 in an anticlockwise direction.

2.14.7

Ellipse

An ellipse or a part of an ellipse can be drawn using the ELLIPSE command. On Menu bar, click Draw, and then in the popup menu click Ellipse, or On Draw panel of the ribbon, click the Ellipse icon shown above, or On the command line, type the command ELLIPSE and press Enter: The prompt sequence is as under: Command: ELLIPSE Specify axis end point of ellipse or [Arc/Center]: Specify other endpoint of axis: Specify distance to other axis or [Rotation]:

In the default C for Center At the last prompt, in Rotation option, type R and then specify the rotation angle (angle at which a circle is rotated to look like an ellipse). The Arc A for this option and press Enter. It further needs the start angle and the end angle measured at the center point of the ellipse from major axis in the anti-clockwise direction. The prompt sequence is as under: Command: ELLIPSE Specify axis end point of ellipse or [Arc/Center]:A [Center]: Specify other point of axis: Specify distance to other axis or [Rotation]: Specify start angle or [Parameter]: Specify end angle or [Parameter/Included angle]:

At the last prompt, either specify the included angle or the end angle. Type I to specify the included angle of the arc and then specify the value of the included angle.

Isocircle In isometric views, a circle appears as an ellipse, known as isocircle. This is very useful for isometric views. See Chapter 10 on isometric views for its use. This option is generally not displayed. It appears only if the

Computer Aided Drafting Isometric Snap is ON function key for different shapes of isocircle for front, side and top view.

2.14.8

23 Isocircle

F5

Donut

On Menu bar, click Draw, and then in the popup menu click Donut, or On Draw panel of the ribbon, click the Donut icon shown above, or On the command line, type the command DONUT and press Enter. Command: DONUT Specify inside diameter : Specify outside diameter: Specify center of donut or :

………………… This prompt repeats Specify center of donut or : Press Enter to terminate the command If FILL mode is OFF, only two concentric circles are drawn with radial lines. If Fill mode is ON, a fully darkened circle is drawn. Fill mode can be set by FILL command and then set it on or off.

2.14.9

Hatch

Drawing a regular pattern inside a closed boundary is called hatching. To do hatching, click on the icon shown above or use BHATCH command on the command line. Boundary Hatch and Fill dialog box is displayed. Click on the Hatch tile. In the Type combo box, select . Click the down arrow in the Pattern combo box and choose a pattern from the list. Click the Pick Points icon on right side. The dialog box disappears and the drawing is displayed. Click any where in the area within the boundary. Dashed lines will display the selected boundary. Press Enter key. The Boundary Hatch and Fill dialog box is displayed again. Click Preview OK button. This command is described in detail in Chapter 9 on sectional views.

2.14.10

Text

current text style, which becomes the default font and format setting. This can be changed to customize the text appearance. The prompt sequence is as under: Command: TEXT Specify starting point of text or [justify/ Click at a point from where the text is to start Style]: Type a number to specify height of letters Specify Height:

Enter Text:

Specify angle if line of text is to be inclined Type the text and press Enter

………….

This prompt repeats

Specify rotation angle:

Press Enter to quit the command Enter text: This command is described in detail in Chapter 6 on Lettering. The other icons of the Draw panel will be discussed where ever required.

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Example 2 Draw all the objects as shown in Fig. 2.S2. This example demonstrates setting, Object Snaps, use of Draw commands LINE, CIRCLE, POLYGON, ARC and ELLIPSE This drawing example has the following entities: 1. A rectangle of size 50 mm 30 mm 2. An equilateral triangle of 50-mm side created by lines on the top side of the rectangle 3. A hexagon of each edge 30-mm on right vertical side of the rectangle 4. A semicircular arc of 15-mm radius on left vertical side of the rectangle 5. A TTT (Tangent, Tangent, Tangent) circle, tangent to 3 sides of the triangle 6. A circle of 10-mm radius at the center of the hexagon 7. An ellipse within the rectangle of 50-mm major axis and 30-mm minor axis 8. One horizontal line passing through the centers of the arc and hexagon extreme edge 9. A donut in the center of rectangle 10. One vertical line from the apex of triangle to the base of the rectangle 11. Second vertical line from the top apex of hexagon to its bottom apex

Solution 1. Open a and set the Limits and Units as given in Example 1. Set the Grid and Snap spacing as 10 mm. 2. Set the objects snaps. At the command prompt, type DDRMODES and press Enter. Drafting settings dialog box appears. Click the Object Snap tab on the top. In the Object Snap window, click on the squares of Endpoint, Midpoint, Center, Tan. Perpendicular and Intersection. A tick ( ) sign will appear. If this sign exists, just leave it there. Click OK button.

Fig. 2.S2

3. To make a rectangle of size 50

Example on Draw Commands

30 mm type Rectang and press Enter.

Command: RECTANG Fillet/Thickness/Width]:

Click on the lower left grid point on the screen

Computer Aided Drafting

25

Move the mouse by 5 divisions of the grid horizontally and 3 divisions vertically and click there. This action draws a rectangle of 50-mm width and 30-mm height as grid spacing is set as 10 mm. Alternately at the second prompt you can also specify the relative coordinates as @50,30 and press Enter. 4. To draw lines for the triangle use LINE command or L. Specify other corner point or [Dimensions]:

Command: L Specify next point or [Undo]: @50:

Select the small rectangle Press Enter or the right mouse button Click at the bottom of left vertical line Click at the bottom of right vertical line of big rectangle X axis). At the next prompt, bring the

mouse at middle of upper line of big rectangle and click.

Computer Aided Drafting

Fig. 2.S3

35

Use of Modify Commands

Note: A triangle sign appears at midpoint. If not, then press F3 function key or ensure that Object snaps are set ON as given in Step 2 above. B. Modifying the basic drawing 8. Rectangle is a set of 4 combined line entities. Break it into separate entities using EXPLODE command. After giving the command, click on big rectangle and then the small rectangle. 9. Fillet the inclined lines by 10-mm radius. Follow the sequence given below: Command: FILLET Type R to change the value of radius Trim]:R 10 Select any inclined line Trim]: Select second object or [Polyline/Radius/ Select the other inclined line Trim]: 10. Fillet the right side of small rectangle Press Enter to reactivate previous command

Command:

Type R to change value of the radius Trim]:R 15 Select upper line of small rectangle Trim]: Select second object or [Polyline/Radius/ Select second line of small rectangle Trim]:

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36

Command: CHAMFER Type D for distance option Method]: D Type 50 and press Enter

50

Type 10 and press Enter

Specify second chamfer distance :10 Method]:

Select second object or [Polyline/Distance/Angle/Trim/ Click on the left line Method]: Command: OFFSET Specify offset distance or Through : 5

Type 5 and press Enter

Select object to offset:

Click on left inclined line

Specify point on side to offset:

Click on right of the same line

Select object to offset:

Click on right inclined line

Specify point on side to offset:

Click on left of the same line

Select object to offset: Specify point on side to offset: Note:

Click below the arc between the lines

In the step given above, you will notice that the offset inclined lines are of the same length as the original lines. Hence, the right offset line cross the rectangle, while the left offset line does not touch the rectangle.

Command: TRIM Select cutting edges... Select objects:

Select the upper horizontal line of big rectangle

Select objects:

Press Enter

Select object to trim or shift-select to ex- Click on right offset line which extends in rectangle tend or [Project/Edge/Undo]: Select object to trim or shift-select to ex- Press Enter tend or [Project/Edge/Undo]:

Command: EXTEND Select objects:

Select upper horizontal line of big rectangle

Select objects:

Press Enter

Select object to extend or shift-select to Click on right offset line trim or [Project/Edge/Undo]: Select object to extend or shift-select to Press Enter trim or [Project/Edge/Undo]:

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37

Command: BREAK Select object:

Click on upper horizantal line of big rectangles

Specify second break point or [First point]: Type F and press Enter F Click at lower corner of left offset line Specify second break point:

Click at lower corner of right offset line

HATCH command for this. Boundary Hatch and Fill dialog box is displayed. It is not a Modify command and its icon is on the Draw toolbar. Click on the Hatch tile. In the Type combo box, select . Click the down arrow in the Pattern combo box and choose Solid. Click the Pick Points icon on right side. The dialog box disappears and the drawing is displayed. Click anywhere in the area within the inclined lines and offset lines. The selected boundary will be displayed by dashed lines. Press Enter key. The Boundary Hatch and Fill dialog box is displayed again. Click OK button. 17. Stretch the front curved portion by a length of 5 mm. Command: STRETCH Select objects: Specify other corner:

Make a crossing window by mouse over right arc and half of horizontal lines of small rectangle

Specify base point or displacement:

Click on the right extreme end

Specify second point of displacement:@5,0

Specify the distance and press Enter

18. Increase the Length of the rear tail by 30% using LENGTHEN command. Command: LENGTHEN Select an object or [DElta/Percent/Total/Dynamic]: Type P for percentage option P Enter percentage length : 130

130% of the original length

Select an object to change or [Undo]:

Select the rear tail line

Select an object to change or [Undo]:

This prompt repeats. Press Enter to quit

19. Rotate the tail by 30 degrees. Command: ROTATE Select objects:

Select the rear tail line

Select objects:

Press Enter or click the right mouse button

Specify base point:

Select the right end of the tail line for rotation

Specify rotation angle or [Reference]: 30

Specify the angle of rotation and press Enter

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20. Mirror the drawing about the bottom horizontal line using MIRROR command. Command: MIRROR Select objects:

Select the entire drawing by making a window

Select objects:

Press Enter or click right mouse button Click at left end horizontal bottom line

Specify second point of mirror line:

Click at right end of the same line

Delete old objects?[Yes/No]:

Press Enter

21. Reduce the size of whole drawing by 20%. Command: SCALE Select objects:

Select the whole drawing by a window

Select objects:

Press Enter or click right mouse button

Specify base point:

Click on left end middle

Specify scale factor or [Reference]: Specify scale factor and press Enter 0.8

THEORY QUESTIONS 1. Describe the various displays on an AutoCAD screen. 2. What is a ribbon? How can it be displayed and closed? 3. Describe the functions assigned to Function keys (F1 to F11) in AutoCAD. 5. 6. 7. 8. 10. 11. 12. 13. 14. 15. 16.

What types of coordinates can you use in AutoCAD? Write their syntax. Describe the use of LIMITS command? How will you use it? What do you mean by Snap and Grid? Describe their use. Explain the use of Object Snap. Discuss the different modes of operation. What are the various types of lines offered by AutoCAD? Describe them. Give the command sequence to make an equilateral triangle using three lines. Write any 3 options to draw a circle. Describe the method to draw an arc. Describe the method to draw a rectangle in AutoCAD. Give the prompt sequence to draw an ellipse. By giving a sketch, explain the use of MIRROR command.

18. Explain the use of ROTATE command. 19. What is the utility of SCALE command? Can you have different scales in X and Y directions while using this command? 20. What is the difference between BREAK and TRIM command? Explain the use of these commands by giving an example. 21. How do you use a CHAMFER command to specify different chamfer distances for each side. command with zero radius? 23. What is meant by GRIPS? How are they used for editing? Differentiate between a cold, a warm and a hot grip.

Computer Aided Drafting

39

VIVA-VOCE QUESTIONS 1. What are the advantages of Computer Aided Drafting.

4. 5. 6. 7. 8. 9. 10.

What type of various units you can use in AutoCAD? How do you set the units? Differentiate between Pan, Move and Zoom. How do you pan a drawing? What is the utility of ORTHO command? How is it activated and deactivated? How will you draw a polygon with given center and an edge length? What is the difference between Window and Crossing window while selecting an object? What is the difference between COPY and MOVE command? Explain by examples. Explain the use of EXPLODE command.

MULTIPLE CHOICE QUESTIONS 1. AutoCAD is a software for (a) drafting (c) designing and drafting 2. Menu bar on the AutoCAD screen contains (a) File, Edit, View, etc. (c) Cut, Copy, Paste, etc. 3. Commands given in AutoCAD appear (a) in the drawing area (c) at the command line 4. Ortho, Snap, Grid, etc. are displayed on the (a) object snap toolbar (c) right hand side menu 5. Text within conical brackets means that (a) it requires some more values (c) it is the last priority option

(b) designing (d) drafting and manufacturing (b) Draw, Modify, etc. (d) None of the above (b) on the toolbar of commands (d) at the status line (b) view toolbar (d) status bar (b) the value will be transferred to the next command (d) it is the default option or value

(a) indicates the X and Y direction arrows with type of coordinates (b) indicates the X and Y direction only (c) displays the coordinates (d) displays the relative coordinates 8. The coordinates that AutoCAD can use, are (a) only Cartesian (b) Cartesian and polar (c) Cartesian and spherical (d) Cartesian, polar and spherical 9. Maximum limits of a drawing in AutoCAD (a) can be A4 size (b) can be A3 size (c) can be A0 size (d) depend upon the hardware 10. PAN command is used to move the drawing over the screen (a) vertically (b) horizontally (c) in any direction (d) in Z direction

Part A – Chapter 2

40 11. ZOOM command is used to (a) increase the size of drawing (c) decrease the size of drawing

13.

14.

15.

16.

17.

(b) increase or decrease the size of drawing (d) move the drawing

(b) can have different distances in X and Y directions at 45 degrees (c) can have different distances in X and Y direction at zero or 30 degrees (d) can have different distances in X and Y direction at any angle Snap is turned on or off using function key (a) F4 (b) F6 (c) F7 (d) F9 Function key F8 is used to toggle (a) Coordinate display (b) Grid display (c) Status bar (d) Ortho Object snap is used to increase (a) speed, accuracy and ease of drafting (b) speed of drawing (c) accuracy while drafting (d) memory utilization Object snap can be put off/on by using Function key (a) F8 (b) F5 (c) F3 (d) F1 AutoCAD environment settings can be seen by the command (a) OSNAP (b) DDRMODES

18. LINE command is used to draw (a) only one line segment (c) any number of line segments in continuation

(b) two line segments (d) any number of lines in discontinuation

(a) center and a point on periphery (c) any two points on periphery

(b) two diametrically opposite points on periphery (d) two diametrically opposite points on a horizontal line 20. The Direction option in ARC command is the direction of a (a) tangential line at the end point (b) tangential line at the start point (c) radial line between the center and start point (d) radial line between the center point and end point (a) four corner point (b) two points in the X direction and one point in the Y direction (c) one point in the X direction and two points in the Y direction (d) two diagonally opposite corner points 22. A construction line is (a) an extension of an existing line

(d) a vertical line from a point 23. In ELLIPSE command the values to be given are (a) two points on major axis and two points on the minor axis (b) two points on one axis and one point on the other axis

Computer Aided Drafting (c) center point and a radius (d) center point, lengths of major and minor axes 24. Rotation option in ELLIPSE command draws an ellipse whose

(d) major/minor axis ratio becomes equal to sine of the rotation angle 25. COPY command allows to make (a) only one copy of a single entity at a time (b) many copies of many objects (c) one or many copies of one or many objects (d) many copies of only one entity 26. MIRROR command is used to make (a) a copy of an object (b) a mirror copy of an object with or without original object (c) a mirror copy of an object only about X axis (d) a mirror copy of an object without original object 27. OFFSET command at a time allows offsetting an object

(c) only on one side of object at a variable distance (d) on both sides of object at a variable distance 28. SCALE command is used to (a) only increase the size of a drawing to any scale factor (b) only decrease the size of drawing to any scale factor (c) increase/decrease to any value of the scale factor 29. While using STRETCH command, the object to be stretched has to be selected by: (a) a crossing window (b) a window (c) directly picking the object (d) Fencing 30. LENGTHEN command allows you to increase or decrease (a) incremental length (b) percentage of original length (c) total length (d) any one of the options given above 31. In TRIM command (a) both cutting edge and object to be trimmed have to be only one each (b) cutting edges can be more than one but object to be trimmed should be only one (c) cutting edges can be more than one and objects to be trimmed can also be more than one (d) only one cutting edge but objects to be trimmed can be more than one 32. EXTEND command is used to extend (a) a line only (b) a line or arc (c) only arc (d) spline 33. To cut a portion of a circle using a BREAK command (a) there have to be two cutting edge entities (b) one cutting edge and one break point is required

34. In CHAMFER command, the distances for chamfer (a) have to be equal and can be given in any order (b) can be equal or unequal and can be given in any order

41

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42

(c) can be equal or unequal and the order depends upon selection order of lines to be chamfered (d) none of the above 35. FILLET command is used to modify corners with an arc of (a) any radius (b) radius within a possible range (c) only zero radius (d) very large radius 36. A Grip is used to (a) stop an object from moving (b) lock an object so that its properties could not be changed (c) do some modify operations (d) to hide the drawing

ANSWERS 1. 7. 13. 19. 25. 31.

(a) (a) (d) (b) (c) (c)

2. 8. 14. 20. 26. 32.

(a) (d) (d) (b) (b) (b)

TO

3. 9. 15. 21. 27. 33.

MULTIPLE CHOICE QUESTIONS

(c) (d) (a) (d) (a) (d)

PROBLEMS

4. 10. 16. 22. 28. 34.

FOR

(d) (c) (c) (c) (c) (c)

5. 11. 17. 23. 29. 35.

(d) (b) (c) (b) (a) (b)

6. 12. 18. 24. 30. 36.

(b) (c) (c) (c) (d) (c)

PRACTICE

1. Set limits (0,0) to (1000,600) and make a rectangle of size 400 300 with its lower left corner at (200,200). 2. Set units as feet and inches and limits of (0,0) to (60,40). Draw a rectangle of 30 20 inches. original size. 4. Draw a line of 70 mm length with a circle at each end of radius 10 mm and a circle in the middle of radius 15 mm. 5. Draw a line of length 60 mm and a circle of radius 10 mm with center at (–10,20) from right end. 6. Draw a line of length 80 mm and another line of 40 mm at right angles in the middle. Draw a circle of radius 20 mm at their intersection. 7. Draw a circle of radius 20 mm and a horizantal line of 40 mm from its center. Draw another circle of radius 10 mm at the intersection of line and previous circle. 8. Draw a triangle of any size. Then using perpendicular object snap, draw a line from the vertex to the opposite line. Draw the other two perpendicular lines also. 9. Draw two inclined lines of any size from a comman vertex. Draw a bisector line by using mid object snap of an arc at free ends. 10. Draw a circle of diameter 40 mm and four radial lines of length 30 mm out from the circumference of the circle at each quadrant. 11. Draw a circle of radius 20 mm and four more circles of radius 10 mm at each quadrant. 12. Draw a circle of radius 20 mm and two tangent lines from a point any distance. 13. Figure 2.P1 shows 6 drawings in a grid of 10 mm. Draw them on A4 size sheet. The grid need not be shown. 14. Figure 2.P2 shows 6 drawings in a grid of 10 mm. Draw them on A4 size sheet. The grid need not be shown. 15. Figure 2.P3 shows 6 drawings in a grid of 10 mm. Draw them on A4 size sheet. The grid need not be shown.

Computer Aided Drafting

Fig. 2.P1

43

Fig. 2.P2

Fig. 2.P3

4 4.1

Lines and Freehand Sketching

LINES

Lines are used for many purposes. For example, drawing the main object outline, marking center lines, mentioning dimensions, etc. Figure 4.1 shows various types of lines for different use. Table 4.1 shows various types of lines, their appearance and use.

Table 4.1 Name of a line

Fig. 4.1 Use of Different Line Types

Types of lines and their applications

Appearance

Application of the line

Continuous thick straight line

Drawing the main outline of the object.

Continuous thin straight line

Dimension lines, Extension (Projection) lines, Leader lines, Hatching, Short center lines.

Continuous thin wavy line (Short break line)

Limit of partial interrupt. When a part is narrow and long and that it cannot be completely shown, use this type of line for intermediate break.

Dashed thick line

Showing hidden edges.

Dashed thin line

Also for showing hidden edges. Use either thick or thin line but use any one type in one drawing.

Chain thick

Lines or surfaces of special requirement.

Center line (Chain thin)

Drawing symmetrical objects. Objects are symmetrical about this axis.

Chain thin double dashed

Outlines of adjacent parts, Centroidal lines.

Chain thin, thick at ends and corners

Showing cutting planes. If the cutting plane is straight, only a thin straight chain line with thick ends is shown.

A straight line with an arrow (Leader line)

Refers to a feature like object, dimension, etc. It can have an arrow or a dot.

Continuous thin straight with zigzags (Long break line)

When a part is wide and long such that its length cannot be accommodated on the sheet, it is shown broken by this type of line.

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4.2

PRECEDENCE OF LINES

At times, some of the main lines may coincide with hidden or center lines. Since continuous lines exhibit the shape of the object, they are given priority over all lines. If dashed lines appear over center line, then priority is given to dashed line. Following is the precedence that should normally be used for lines. Top priority

Continuous lines Dashed lines Cutting plane lines Center lines Break lines Extension/dimension lines Section lines

Least priority

4.3

THICKNESS OF A LINE

It is also called line width or line weight in CAD terminology. Pencil lines are generally drawn thinner than

Table 4.2 Thickness

Line thicknesses with pencil and ink With pencil

With ink

Thin Medium

0.4 mm

Thick

4.4

DRAWING LINES

of pencil movement for a right hand worker. It will be reverse for a left hand user. To draw a horizontal line, place the T-square tightly against the straight edge of drawing board and draw lines along the straight edge of T-square from left to right (Fig.

the line is to be drawn on left half of the sheet, draw from bottom to top and from top to bottom for right by triangles. Combined use of triangles can draw angles any angle for a line.

Fig. 4.2 Drawing Horizontal and Vertical lines

Lines and Freehand Sketching

4.5 4.5.1

61

FREEHAND SKETCHING Introduction

In the process of engineering design, the first step is conceptual design, i.e. formulation of idea in mind. This concept has to be transferred on paper, generally by freehand sketching because it is in In freehand sketching, drawing is made using pencil and eraser without the aid of other drawing instruments. Hence to make a good sketch, it is necessary that one should be able to draw straight lines, curves, etc., without any external aid. In the beginning, one should practice to draw horizontal and vertical lines. It may not be exactly to scale, but it should be proportional for better understanding. Following methods are suggested to make some drawing entities:

4.5.2

Drawing Freehand Lines

Straightness of lines comes with experience and by using proper strokes. Horizontal lines should be drawn the hand may have to be stretched a little at the ends and contracted in the center to keep the line straight. The dashed position of the pencil shows the displaced position after drawing a portion of the line. For long lines that

the hand touching the paper and wrist in lifted position.

(A) Drawing horizontal lines

(B) Drawing vertical lines

Fig. 4.3 Drawing Horizontal and Vertical lines by Freehand

4.5.3 Center Lines distances should be maintained with this line rather than with extreme boundaries.

4.5.4

Diagonals

Intersection of diagonals of a rectangle gives the geometric center. This center can be used to draw the center line if not drawn earlier. Diagonals can also be used to increase or decrease the size of the rectangle/drawing, keeping the same geometric center (Fig. 4.4A) or by keeping one corner same and extending the other corner. In Fig. 4.4B the rectangle in dashed line is scaled up using diagonals.

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62

Fig. 4.4

4.5.5

Use of Diagonals

Fig. 4.5

Drawing a Freehand Circle

Circles

Mark four arcs on these axes at distances equal to the radius.

4.5.6

Proportioning Sizes

The easiest way of proportioning an object can be explained as follows: Draw one axis of length so as to represent the longest dimension of the object. Divide the longest size into , etc. as required. divide it into two parts, each part being 100 mm. Then again divide this half into two equal proportions, each

Fig. 4.6

Measuring Distances with Pencil and Thumb

mm, and so on. distance being measured from the nail of the thumb to the pencil point from the line drawn. the method discribed earlier. Any smaller values should be suitably approximated.

4.5.7

Sketching Pictorial Views

Following steps may be taken as general guidelines for sketching pictorial views. They may have to be slightly changed suitably depending upon the shape of the object. Select the size of the drawing sheet for the object size. Sketch the front, side and top view proportionally before Orient the object in your mind at an angle that will show maximum details.

Fig. 4.7 Freehand Sketching of Pictorial View

Lines and Freehand Sketching

along Y axis.

Example 1

Solution

Fig. 4.S1 Sketching a Flywheel

Example 2

Solution

Fig. 4.S2

Sketching a Ratchet

Example 3

Solution

Fig. 4.S3

Sketching an Angle Block

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CAD 4.6 4.6.1

LINES USING CAD Linetypes

For machine drawing, many types of lines such as continuous lines, dashed, center lines, etc., are used. There are standard conventions about the use of type of a line. AutoCAD offers many types of lines in a library from where you can choose various linetypes. New linetypes can also be designed. The scale is to be changed according to the size of the drawing and the type of the line. All linetypes except continuous have to be loaded before they are used. They are loaded by DDLTYPE command. Command: DDLTYPE or LTYPE and press Enter.

A Linetype Manager dialog box is displayed. Click on the right-hand side button Load…. It displays Load or Reload Linetypes dialog box. Click on the desired linetype to highlight it. To add more than one line to the selection, hold Ctrl key and click the other lines. Click OK Button at the bottom of the dialog box.

4.6.2

Object Properties

A line is an entity in CAD. AutoCAD entities have properties like Color, Linetype, Lineweight, Layer and Plotstyle. By default, an entity is drawn in a black/white color, with a continuous linetype, default lineweight (line thickness) on zero layer. Properties can be set using the Properties panel at the Home tab of the ribbon as shown in Fig. 4.8A. If this panel is not visible, then right click the mouse button anywhere on the ribbon and then from the popup showing Tabs/Panels, click on Panels. It displays another popup menu. Click on Properties. A tick sign is displayed on its left side.

Fig. 4.8 Properties Panel

Lines and Freehand Sketching

65

The Properties panel has 4 boxes each with an arrow on the right side. The topmost box is to set the color. Click on the arrow on its side. A popup menu showing colors is displayed (Fig. 4.8B). Choose a color from the options. Or click on Select colors… to see many more colors. The second box from the top is to set lineweight (thickness of a line). Click on the arrow on its side. A popup menu showing different lineweights is displayed (Fig. 4.8C). Choose a lineweight from the options. Or click on Lineweight settings … at the bottom. It displays a dialog box as shown in Fig. 4.10. The third box is to set linetype. Click on the arrow on its side. A popup menu showing different options (Fig. 4.8D) is displayed. Choose an options, or click on Other.. at the bottom. It displays a linetype manager If you click the downward arrow at the bottom of the Property panel, it will display two more options. The List option displays the list of all the information about the selected entity. If you see minutely, there is an inclined downward arrow at the bottom right corner of the Property panel. Clicking this arrow displays Properties dialog box as shown in Fig. 4.9. You can modify any property of an entity in this dialog box.

Fig. 4.9 Properties Dialog Box

A.

COLOR

Colors are useful not only to beautify the drawing but offer more clarity. To set a color, click the arrow in the Select color…. You can also set a color by the COLOR command. Command: COLOR or COLOUR and press Enter.

Select Color dialog box is displayed. Choose a color and click OK button. Now all the drawings created after issuing this command will appear in the set colour.

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66

B.

LINETYPE

to load the linetype using DDLTYPE command else they will not be displayed in the list.

Scale For Linetype If you load a broken line such as dashed or center line, sometimes you may be disappointed to see a dashed line as a continuous line. Hence a proper scale factor has to be given. An experience gives you an idea about the scale factors to be used for different types of lines. Select an entity, and change in the Properties dialog box shown in Fig. 4.9. Change the Linetype scale value in the text box of the dialog box. Note: Acadiso template, the default units may be in inches, you may not see a line as dashed. So if working in mm, use the above-mentioned template.

C. LINEWEIGHT Line thickness is called Lineweight in AutoCAD. The second box in the Properties panel (Fig. 4.8C) is to choose lineweight. Click on the arrow and choose a line thickness from the drop-down list. The line thickness the main outline, dimension line etc. has to be different for clarity. You can also set line thickness using LINEWEIGHT command: Command: LWEIGHT and press Enter

Note: The thickness of a line may not change even after setting another lineweight. To see the effect, type LWEIGHT command. Lineweight Settings dialog box is displayed (Fig. 4.10). Click the square Display Lineweight or Press Alt + D. A tick sign will appear. Close the dialog box. Now the effect will be visible. Its effect can be varied by dragging the slider of Adjust Display Scale from Min to Max. Further study: All these Properties can be assigned to a LAYER. Use of this command is explained in

4.6.3

Fig. 4.10

Lineweight Settings Dialog Box

Match Properties

Properties of one entity can be matched with the other entity by any one of the following methods: On command line type command MATCHPROP and press Enter key or Click the icon shown above in the Clipboard panel Fig. 4.11 Clipboard Panel of the Home tab on the ribbon (Fig. 4.11). When you click the icon or type the command, you are prompted to select the source object. Click on the entity whose properties you want to match. A brush icon will be attached to the cursor. Click on the other entity or entities whose properties you want to match with source entity. The Cut icon (Fig. 4.11) can be used to cut an entity from one place and paste at other place using Paste icon. The Copy icon is used to create a copy of one entity to be pasted at other place.

Lines and Freehand Sketching

67

4.7 SKETCH COMMAND This command is to draw lines or curves on the screen using a mouse. When this command is used, the next prompt displays Record increment. By default it is 1 unit. When the mouse is clicked, Pen down is displayed. Wherever the mouse is moved, a line or curve is drawn. Next clicking of the mouse puts the pen off. This action toggles. One click puts it on and the other puts it off. Command: SKETCH Record increment : Sketch. Pen eXit Quit Record Erase Connect .

Other commands of AutoCAD can draw with much better quality than this command, and hence this command, is not recommended to use. Example 4 Draw a V belt pulley as shown in Fig. 4.S4. Dimensions need not be given. In this example you learn the following: 1. Use of construction line

4. Set / modify line thickness Fig. 4.S4

Solution

A Pulley Example on Object Properties

Initial Settings RECTANG 0,0 and other as 210,300. ZOOM command and choose All option by typing A and pressing Enter. The rectangle is now displayed to full drawing area. 4. Use DDRMODES command. Drafting settings dialog box is displayed. Click the Object snap bar on the top. On the object snap modes tile, click the square for End, Midpoint, Intersection, and Center modes. Drawing Left View RECTANG 10,100 and the other as @5,100. LINE command. Ensure the Object snap is on. Press F3 to see On/Off. upper right corner of the rectangle. Now press F3 to put it off. Next point @157

–4

–6

–10

–14







–15

–19







Grades Over Up to –

3

140

60

3

6

140

70

6

10

150

10

14

150

300

50

50

65

340

190

100 100

140

10

6

0

6

10

7

0

16 40 40

7

0

50

9

0

10

14

7

14

50

315

355

355

400 450

1500

500

1650

ZA

ZB

ZC

>7

>7

>7

>7

>7

>7

>7

>7

–15



–33



–73

–136

–35

–41

–55

–64

–17

–60

–9

–34

–43

–54

9

–11

–41

–53

–66

150

100

60

30

10

0

13

9

–11

–43

–59

–75

36

0

16

10

–13

–37

–51

–71

–91

36

0

16

10

–13

–37

–54

–79

–104

–65

0

–15

–43

14

0

–15

–43

340

170

100

50

15

0

13

–17

–31

–50

170

100

50

15

0

30

13

–17

–31

–50

–17

170

100

50

15

0

30

13

–31

–50

300

190

110

56

17

0

36

16

–34

–56

330

190

110

56

17

0

36

16

–34

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360

0

39

17

–37

400

0

39

17

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150

–77

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7

14

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13

43

–97

–90

–54

10

–63

–67

–45

0

–43

–64

–39

0

–15

–50

–47

9

0

– –

–41

10

14

–34 –40

–33

–43

43

– –

–134

–70

–97

–146

–300 –360 –335

–190

–340 –310

–310

–400

–365

–470

–415

–535

–465

–600

–350 –310

–196

–170

–350

–190

–390

–475

–590

–435

–530

–660 –740

0

33

43

–40

–330

–490

–595

0

33

43

–40

–360

–540

–660

–690

–700

–730

–1150 –960 –1050

–1350

–1000

–1300

–1700

–900

–1150

–1500

–1900

–1000

–1300

–1650

–790

–1100 –1000

–900 –1000

–710 –650

135

–740

–640 –475

135

–575

–405

–445

–670 –470

–340 –315

–114

–136

–174

–300

–166

–140

–114

–146

–130

–94

–160

–144

–144

–146 –77

–75 –94

–170 –100

–60

–50



–34

145

–40 –35



30

440

Z

–35

–17

43

760

Y



–9

145

600

400

6

145

540

–19

–15

310

1350

450

–15

60

740

1050

6

–10

100

160

315

–7

6

140

460

660

6

5

0

170

160

–7

0

6

410 140

–6

6

5

16

130

360

5

13

65

40

-4

50

110

160 170

3

40

50

300

0

6

5

65

310

4

0

95

30

0 4

110

40

6 10

150

X

Grades

30

160

30

65

14

V

Tolerances, Limits and Fits

14

95

All

U

–1550

–1450 –1600

371

372

Table 19.6

Fundamental deviations for shafts

Upper deviation in microns Diameter in mm

a

b

c

d

All

All

All

All

e

Lower deviation in microns

f

g

h

JS

j

j

All

All

All

All

5,6

7

Grades Over Up to –

3

–140

–60

3

6

–140

–70

6

10

–150

10

14

–150

14 –300

65 100 100

140

–5

0

–16

–6

0

–3

–6

3

7

–6

4

7

–16

315

355

355

400

–1350

–6

0

–3

–7

0

–4

–40

–7

0

–4

–50

–9

0

–5

–10 –10

–50

400

450

–1500

450

500

–1650

–760

y

z

za

zb

zc

6

10

15

All

All

All

All

All

All

All

14













19

15 15





34



33



40



50

64 77

33

39

45



60



41

47

54

63

73

35

41

55

64

75

34

43

9

17

60

–9

0

–5

34

43

54

–30

–10

0

–7

11

41

53

66

–150

–100

–60

–30

–10

0

–7

11

43

59

75

–36

0

–9

–15

3

13

37

51

71

91

–36

0

–9

–15

3

13

37

54

79

104

–43

–14

0

–11

3

15

43

63

–145

–43

–14

0

–11

3

15

43

65

–145

–43

–14

0

–11

3

15

43

–170

–100

–50

–15

0

–13

4

17

31

50

–100

–50

–15

0

–13

4

17

31

50

17

–170

–100

–50

–15

0

–13

4

31

50

–300

–190

–110

–56

–17

0

–16

4

34

56

–330

–190

–110

–56

–17

0

–16

4

34

56

–360

0

4

37

–400

0

4

37

–135

0

5

40

–135

0

5

40

134

70

97

146

140

360

310

400

300

365

470

340

415

535

465

600

575

740

640 475

390

475

590

435

530

660

330

490

595

740

360

540

660

690

700

730

1150 960 1050

1350

1000

1300

1700

900

1150

1500

1900

1000

1300

1650

790

1100 1000

900 1000

710 650

405

445

670 470

350

190

300

174

340 315

114

136

350 310

170

114

310

196

150 136

335

190

166

94

130

160

146

130

97

90

144

144

146 77

67

94

170 100

60

50

– –

17

–145

40 35

35

9

–170

All

19

–60

–440

x

10

–100

–340

–600

–5

–40

v

15

–140

–740

–540

6

–13

–310

–1050

4

–50

160

315

All

–40

–460

–660

All

–95

–170

160

All

4

–410 140

All

1

–130

–360

All

0

–65

–190

65

–6

u

Grades

4-7

–4

–110

–340

50

50

All

Grades

–4

–65

–160

t

0

–50

–170

s

0

–95

–300

r

–4

–110

–310

p

–10

–150

30

n

–30

–160

40

40

–14

m

1550

1450 1600

Part D – Chapter 19

30

All

k

Tolerances, Limits and Fits

Fig. 19.5

19.5.2

Interpretation of Upper Case Letter Symbols

Letter Symbol for Shafts

Figure 19.6 shows fundamental deviation for the shafts, which is the mirror image of Fig. 19.4.

Fig. 19.6

Graphical Illustrations of Tolerance Zones for Shaft

Note the following from this Fig. 19.6. b. Maximum negative upper deviation is for letter a. Also see its meaning in Fig. 19.7A. c. Upper deviation is zero for letter h. See Fig. 19.7B also.

deviation for these letters is equal to the lower deviation + IT grade see Fig. 19.7C also.

Fig. 19.7

Interpretation of-lower Case Letter Symbols

373

Part D – Chapter 19

374

19.6

PLACING A DIMENSION WITH TOLERANCE

Four methods are used for placing dimensions with tolerances:

19.6.1

Basic Size with Deviations

In this method, the basic size followed by its tolerances is placed above the dimension line. Tolertolerance is put above the negative tolerance. These deviations may be equal or unequal. Text size of tolerances numbers is kept smaller than the text size of the basic value. If the deviation is both in + and – side, it is called Bilateral tolerance unequal. If one of the deviations is zero it is called Unilateral tolerance.

Fig. 19.8

19.6.2

Placing the Tolerated Dimension

Maximum and Minimum Limits

In this method, instead of placing the deviations, both maximum and minimum limits are placed over the dimenplaced. The precision of both the tolerance values (places after the decimal point) should be kept same, e.g. 50.1

The above two mentioned methods are applicable to angular dimensions also.

19.6.3

General Notes

If tolerances are same for all the sizes, a general note can be written as below: If tolerances are dependent on some range of sizes a tabular statement can be made as shown in the box:

Dimension (mm)

Tolerance

19.6.4 Basic Size with Fundamental Tolerances

Up to 100

± 0.01

300 to 500 More than 500

± 0.05 ± 0.10

In this method, the basic size is followed by the fundamental tolermating parts both hole and shaft dimensions can be together. For example: 50H7/50C9. First value is for hole and second value is for the shaft. Meaning of each character is shown in Fig. 19.9.

19.7

CUMULATIVE TOLERANCES

If the dimensions are given in succession all the tolerances get accumulated to give a large value of tolerance, it is said to be cumulative tolerance (Fig. 19.10A). The overall total positive tolerance

Tolerances, Limits and Fits

Fig. 19.9

Basic Size with Fundamental Tolerances

Fig. 19.10

375

Cumulative and Non-cumulative Tolerances

Example 1 Figure 19.S1 shows overall limits on length as 100.0 and 99.5. Two holes are drilled at equal distance from center line at distance of 30 mm. Calculate the limits for size A. The same tolerance as of A is applied for the vertical distance between the center lines of the circles. Calculate the limits for size B.

Solution Size A is maximum when size 100 is maximum and tolerance on size 30 is minimum. Hence: Size A is minimum when size 100 is minimum and tolerance on size 30 is maximum. Hence:

Since B = 3A, hence maximum size of B = 60.06 and minimum size = 59.19. or B = 60

Example 2 deviation is shown in microns by shaded area for 5 cases from A to E. Calculate the following for each case:

Fig. 19.S1

Example 1

Fig. 19.S2

Example 2

Part D – Chapter 19

376

Solution PROBLEM

(A)

(B)

(C)

(D)

(E)

)

+ 15

0

–5

– 30

– 40

Upper deviation ( )

+ 30

+ 10

+ 10

0

– 15

79.995

79.970

79.960

Upper limit size (mm)

Example 3 59.7 mm respectively. Find its fundamental deviation zone and IT grade tolerance.

Solution

is nearest to 190, i.e. zone ‘b’.

Example 4

Solution

Example 5 under:

Calculate maximum and minimum sizes of the holes for the fundamental tolerances given as

Solution Fig. 19.4 also. From Table 19.2 Case

Basic size

Range

IT Grade (ITG)

A

45

30-50

7

B

50

30-50

Tolerance value 39

C

7

30

D

7

30

E F

90

6 54

Tolerances, Limits and Fits

377

From Table 19.5 Upper

Basic size

Range

A

45

40-50

B

50

40-50

Tolerance zone

Tolerance value in

Upper or lower

+9 H

0

P

– 37

Upper

ZC

– 690

Upper

C D E

90

F

A. 45G7 Table 19.5 for holes as + 9 i.e. 0.009 mm. Therefore minimum size is 45.009 mm. fore maximum size is minimum size + IT grade = 45.034 mm. B. 50H8 For basic size 50 mm, the range is 40 to 50 mm under the tolerance Zone H see the lower tolerance value in Table 19.5 for holes as 0 or 0 mm. Therefore minimum size is 50 mm. , i.e. 0.039 mm. Therefore maximum size is 50 + 0.039 = 50.039 mm. C. 80J7 Table 19.4 for 80.018 mm. T grade 7, tolerance value 30 i.e. 0.030 mm. There80.048 mm. D. 80JS7 Table 19.5 for , i.e. 0.030 mm. = 0.015 mm. Hence answers are: maximum size = 80.015 mm and minimum size = 79.985 mm. E. 90P6 Table 19.5 for holes as –37 , i.e. –0.037 mm. Therefore maximum size is 89. 963 mm. 89.941 mm. F. 120ZC8 Table 19.5 for holes as – 690 , i.e. 0.690 mm. Therefore maximum size is 119.310 mm. i.e. 0.054 mm. Hence minimum size = 119.310 – 0.054 = 119.256 mm.

Part D – Chapter 19

378 Example 6

Calculate the maximum and minimum sizes of the shafts for the fundamental tolerances given

as under:

Solution A. 35d7 From Table 19.6 upper deviation Hence maximum size is = 34.92 mm. 34.895 mm.

B. 60h8 From Table 19.6 upper deviation for basic size 60 mm, under tolerance zone h, the value is 0. Hence maximum size = 60.000 mm. , i.e. 0.046 mm. Hence minimum size is = 60.000 – 0.046 = 59.954 mm. C. 85js10 , i.e. 0.14 mm. 84. 93 mm. 85.07 mm. D. 95 m6 From Table 19.6 upper deviation for basic size 95 mm, under tolerance zone m the value is + 0.13 , i.e. + 0.013 mm. Hence minimum size is = 95.013 mm. 95.035 mm.

Example 7

A bracket as shown in

tolerances.

Solution Refer Table 19.4. For sand casting process, tolerance grade obtainable is IT16. Note the following values for the sizes required (shown bold for the ranges given in the table) and calculate the tolerances as under:

Fig. 19.S7A

A Bracket

Basic size

Range

IT16 tolerance ( )

Total tolerance (mm)

Symmetric tolerance

10

6-10

900

0.9

± 0.45

18-30

1300

1.3

± 0.65

1.9

± 0.95

40

30-50

1600

75

50-80

1900

180-250

2900

Tolerances, Limits and Fits

379

The tolerances are rounded to one decimal place as sand casting cannot give that much accuracy. These tolerances are indicated on the drawing as under in Fig. 19.S7B:

Fig. 19.S7B

Solution to Example 19.S3A

Example 8

Fig. 19.S8A

A Stepped Shaft

Solution Refer Table 19.4. For turning using capstan lathe, tolerance grade obtainable is IT9. Note the following values for the sizes required (shown bold for the ranges given in the table) and calculate the tolerances as under: Basic size Range IT9 tolerance ( ) Total tolerance (mm) Symmetric tolerance 30 18-30 52 35 30-50 62 40 30-50 74 0.074 ± 0.037 75 80-120 87 The tolerances are indicated on the

Note: Tolerance value on end diametions .

19.8

FITS

19.9

SYSTEMS OF FITS

Fig. 19.S8B Solution to Example 19.S4A The dimensional relation between the mating parts is known as a Fit. It indicates the tightness or looseness of the mating parts. This is very important for many engineering applications for the satisfactory working of parts in movement such as piston in a

Shaft basis – Upper deviation for the shaft is zero.

Part D – Chapter 19

380

19.9.1

Hole Basis

In this system, basic size is taken as the minimum hole size. Hence lower deviation is zero, i.e. fundamental deviation is H. Shaft diameter is calculated by subtracting the desired allowance from the basic hole size. Tolerances are then applied to each part separately (Fig. 19.11).

19.9.2

Fig. 19.11

Shaft Basis

Hole Basis of Fits

In this system, basic size is taken as the maximum shaft diameter. Hence upper deviation is zero, i.e. fundamental deviation is h. Hole diameter is calculated by adding the desired allowance to the basic shaft size. Tolerances are then

19.10

SPECIFYING A FIT Fig. 19.12

Shaft Basis of Fits

grades on hole and shaft separated by a dash. Some systems use a slash also for separating the tolerances. First tolerance is on hole, and the second tolerance is on shaft. If it is on the hole basis, tolerance grade H is h Tolerance zones (Tolerance letter and IT grade) get interchanged for both, i.e. the tolerance zone of the hole is applied to the shaft and that of shaft is applied to the hole. For example: H7-d8

hole basis the shaft. shaft basis as under:

D8-h7

19.11

shaft basis the shaft. Note the difference in both the systems carefully. IT grade 7 for the hole is now for shaft

TYPES OF FITS

1. Both maximum and minimum clearances are always positive. Maximum clearance is positive and minimum clearance is negative. Negative clearance is called Interference. 3. Both maximum and minimum clearances are always negative.

Tolerances, Limits and Fits

Fig. 19.13

19.12

381

Types of Fits

SELECTION OF FITS

external dimensions of hole and shaft respectively. Allowance is the clearance or interference provided in-

Table 19.7 Hole basis

Shaft basis

Application Clearance Fits

H11-c11

C11-h11

H9-d9

D9-h9

Commercial rough applications pressures Oil seals, splined shafts Slow speed sleeve bearings, plastic bearings Medium speed sleeve bearings, grease lubricated bearings, sliding blocks, sliding gears on shafts Accurate locations with moderate speeds and loads

H7/f 7

F7-h7

H7-g6 H7-h6

A little clearance for main bearings, crank and connecting rod bearings Not for running, but to move or turn freely

H6-h7 mandrels, sliding under manual forces, if lubricated

(Contd.)

Part D – Chapter 19

382

Table 19.7 Hole basis

(Contd.)

Shaft basis

Application Transition Fit

H7-j6

Frequently dismantled parts like keys, pulleys, gear trains, hand

H7-k6

K6-h7

Pulleys, gears, bearings on shafts, Easy joining with hammer

H7-m6

M6-h7

Inner race of the bearings on shafts, Hard joining with hammer

H7-n6

N6-h7 motor shafts Interference Fit

H7-p6

P6-h7

Moving parts with rigidity without much pressure on hub

H7-r6

R6-h7

Valve seats, couplings on shaft ends, Hubs of couplings, Bearing bushes in housing

H7-s6

S6-h7

Hollow part is heated and shaft is put in it. On cooling, it gets liner

H7-u6

U6-h7

Example 9 (FITS)

Calculate the following: a. Tolerance on shaft

b. Tolerance on hole

c. Maximum clearance

Solution Maximum clearance = Maximum hole diameter – minimum shaft diameter Minimum clearance = Minimum hole diameter – maximum shaft diameter

Example 10 Figure 19.S10 below shows schematically tolerances of the shafts by hatched area and on

Fig. 19.S10

Tolerances, Limits and Fits

383

Solution Maximum clearance Minimum clearance

(A)

(B)

35

31

(C)

(D)

(E)

31

13

10

–1

–4

–4

Clearance

Clearance

Transition

Transition

Iterference

Example 11

H8-f8 for a hole of 40 mm.

Solution H means lower deviation is zero hence minimum hole diameter is 40 mm. Maximum hole diameter = Minimum hole diameter + IT grade = 40.000 + 0.039 = 40.039 mm. 39.975 mm Minimum shaft diameter = Maximum shaft diameter – IT grade tolerance = 39.975 – 0.039 = 39.936 mm In Example 11 sizes can be directly found. If not, then the method as explained in Example 11 has to be followed.

Table 19.8

Preferred clearance limits on hole basis

+ Means add to the basic size – Means subtract from the basic size Basic size

Limit

From Up to 1

3 6

3

6 10

Loose running H11

c11

Fit

Max

+60

– 60

Min

0

Max

+ 75

– 70

Min

0

– 145

Max

+90

Min

0

– 170

+110

– 95 – 110

+370

+60

+14 0

+90 +30

0

+36

–40

0

–76

+40

0

+315

+43

–50

+136

+95

0

–93

+50

0

–65

+169

+33

–117

+65

Min

0

30

Max

+130

Min

0

+110

30

40

Max

+160

+440

Min

0

Max

+160

Min

0

Max

+190

– 140

Min

0

– 330

60

+70 –45 –30

16

50

H8

–60

Max

0

+140

–6

+30

+10

+10

0

+16

–16

+6

0

0

–6

0

–16 –34

+40

0 0

+74

–100

0

–174

+100

Fit

+50

+15

–9

+13

0

–14

+5

–6

+35

+61 0

+74 –41

+4

0

–50

0

–30

+106

+30

0

–60

+30

0

0

0

+15

0

0

–9

0

0

+6

–7

+41

–13

0

–9

+50

0

+41

+9

0 –16

0

+7

–9

+46

Fit

–17

0

–50

h6

0

0

+16

H7

–4

+10

+39 0

g6

Locational

H7

–10

0

Sliding

Fit

+39

+450 +130

f7

–13

0 – 130

Close running

Fit

0

16

50

0

d9

+30 +70

10

40

Free running H9

–10

0 0

+50

–11

0

0

+34

0

+41

+9

0

–16

0

+59

+30

0

+49

0 –19

0

+10

(Contd.)

Part D – Chapter 19

384

Table 19.8 Basic size

Limit

From Up to 60 100

Loose running H11

c11

Fit

H9

d9

+190

– 50

+530

+74

–100

Min

0

– 340

+150

0

–174

Min 100

Free running

Max Max

– 170

+610

0

– 390

+170

0

– 400

(Contd.) Close running

Fit

Min 160

Min 160

+710 0

– 530

0

– 570

300

g6

Fit

H7

h6

–10

+59

+30

0

+49

0

–60

+30

0

0 –19

0

+54

–36

0

–71

+54

–36

0

–71

+36

0

–34

–43

+146

+40

–14

+63

+145

0

–170

+400

–170

0 +970

+130

– 650

+330

0

+190

+360

– 400

+140

+450

400

Max Min

0

– 760

400

450

Max

+400

– 440

Min

0

450

500

Max

+400

+155

Min

0

0

+400

0

–190

–350

+155 +440

0

+450

–96

+69 +69

0

+540

+97

+540

+97

0

0 0

0

+57 0

+35

0

+57

0

+65

0

+75

0 +79

0

+40

0

–39

+14

0

–15

+90

+46

0

–44

+15

0

+50

Fit

0

0 0

+46

–15

+90

+46

+50

0

–44

+15

0

–17

+101

+56

0

–49

+17

0

+111

+57

0

+93

0

–36

0

+57

+190

+35

+46

–56 0

–10

0

+43 –96

+10

+35

–50

+170

– 330

300

0

+400

0

+30 +36

–50

+170

Min

Table 19.9

H7 +30

+345

0 +115

Max

Fit +106

–145

0

Max Min

+100 +115

0

f7 –30

0

– 460

Max Min

H8

0

Max

Locational

+46 +100

Max

Sliding

–119

0

–131

0

–131

0

0 0

+63 –60

+63

+75

0

–54

+63

0

0 +103

0

–40

0

+63

0

+103

0

–40

0

–60

Preferred Transition and Interference limits on hole basis

+ Means add to the basic size – Means subtract from the basic size Basic size

Limit

From

Up to

1

3

3

6 10

6

10 16

Transition

Transition

Interference

H7

k6

Fit

H7

n6

Fit

H7

Max

+10

+6

+10

+10

+10

+6

+10

Min

0

0

–6

0

+4

–10

0

+9

+11

Min

0

+1

–9

0

Max

+15

+10

+14

+15

Min

0

+1

– 10

0

0

+1

Max

Max Min

+16

+17

Fit

H7

+4

+10

+6

+4

s6

0

+14

0

+19

0

–16

0

+19

+5

+15

+10

–19

0

+6 0

p6

Interference

0 +15

Fit

H7

–4

+10

+31 0

+15

+15

0

0 +39

0

u6

Fit

0 –7

0 0

Interference

– 10 –39

0

–11 –31

+37

–13 –37

+44

–15

+33

–44

(Contd.)

Tolerances, Limits and Fits

Basic size From

Up to

16

30

Limit

Transition H7

Max Min

k6 +15

0

Fit

Table 19.9

(Contd.)

Transition

Interference

H7

n6

0

+15

+19 – 15

Fit

H7

+6

30

40

Max

40

50

Max Min

0

0

+17

–33

0

50

60

Max

+30

+30

+39

+10

+30

Min

0

0

–39

0

Max

+30

+30

+10

+30

Min

0

0

–39

0

Max

+35

+35

Min

60 100 100 160 160

300 400 450

0

+17

Min

0

Max

+35

+3

– 01

Min

0 +40

+3

Min

0

+3

Max

+46

+33

Min

0

+4

Max

+46

+33

Min

0

+4

+37

–33

– 33

+35

+35 –45

+45

+51

0

+37 +59 +37

0

– 45

0

+13

+40 0

+43

+43 +43

–51

0

–5

+30

–51

0

+59

+35

+93

–59

0

+79

–101

0

+144

–116

+40

–61

+40

0

+100 +151

+60

+15

+46

+79

–4

+46

0

+31

–60

0

+50

–79

0 0

+170

+4

– 40

0

+37

Max

+63

+45

Min

0

+4

Max

+63

+45

Min

0

+4

+63 0 +63 0

–66

0 +57

–73

–76

+46 0

+169

–94

+46

+140

–169

0 0

+350

–151

+57

+471

0

0

+435

+63

+63

+530

0

0

+490

+63

+63

+56 –5

+57

–5

0 –5

0

Example 12

Solution The basic size is given for cylinder casing and hence hole basis H7-s6.

Tolerances for shaft are + 93 and + 71. Hence

–150 +190

–151

0

+63 +40

0

–146

–190 +313 –313

–4

+63 +40

+146

–3

+46

0

+35

–59

0

Min

0 –36

–4 0 9

+46

+73

–57 –106

+166

–4

+34

0

0

–79

0

+70 +106

+35

+50

+57

0 +30

–93

+79

+53

–59

– 44

0

– 36

–76

+71

+46

+4

+60

+101

–60

+40

–54 –35

0

+15

0

0

+41 +76

+35

+60

+57

+54

+30

+31

Min

Fit

–45

+53

0

Max

–59

u6

+59

+46

400

H7 0

+30

+59

+35

Fit

+59

0 +51

Interference

–14

0

+66

– 45

0

–35

0

+40

+36

– 45

s6

–1

0 – 33

H7

–1

+45

0 +35

Max

+39

Max

500

+35

+33

300

450

Fit

+33 0

Interference

p6

0

385

0

– 471 –530 – 471

+540

386

Part D – Chapter 19

Maximum interference = Minimum hole diameter — Maximum shaft diameter Minimum interference = Maximum hole diameter — Minimum shaft diameter Same values as –36 and –93 can be seen directly from Table 19.9

Example 13 45.000 mm respectively. Maximum and minimum shaft diameters are 44.991 and 44.975. Find the following:

Solution a. Zero lower limit is for the hole. Hence it is based on Hole system. . IT grade 7. Hence tolerance grade for the hole is H7. c. Tolerance grade on shaft = Difference in maximum and minimum diameters = 0.016 mm i.e. 16 . IT grade 6. , hence from Table 19.6. This value is for tolerance letter g. Hence tolerance grade for the shaft is g6 H7-g6

Example 14 having journal diameter 60 mm such that diameter/clearance ratio remains within 500 to 1000.

Solution The clearance is very important for the design of journal bearings and it has to be kept in a narrow range for the satisfactory operation of the bearing. Since the journal diameter is given, hence shaft basis Tolerance letter symbol for shaft basis is h. Minimum clearance = 60/1000 = 0.06 mm Hence range of tolerance Dividing this equally both for shaft and hole, the tolerance Therefore: Maximum shaft diameter = 60.00 mm Minimum shaft diameter = 60.00 – 0.03 = 59.97 mm Minimum hole diameter = Maximum shaft diameter + minimum clearance = 60.03 + 0.03 = 60.06 mm Maximum hole diameter = Minimum hole diameter + tolerance on hole = 60.6 + 0.03 = 60.09 mm IT7 both for shaft and hole. Hence tolerance for shaft is h7. Tolerance letter for the hole of 60 mm basic size (50 to 65 mm range) for a lower deviation of 60 (0.060 mm) is E from Table 19.5. E7-h7 To have a tolerance grade of IT7, the process required for the journal and bearing is Precision turning (Table 19.1)

Tolerances, Limits and Fits

19.13

387

FITS FOR THREAD FASTENERS

Fit for thread fasteners depends upon tolerance value and positions tolerance for the mating parts. Position tolerance is the distance between the basic size and the nearest end of the tolerance zone called fundamental deviation. IT grade fundamental deviation

19.14

GAUGES

like vernier caliper, micrometer, angle protractor etc. consume a lot of time in taking reading. These instruments can be used for one or two jobs or even for a small batch, but it is highly inconvenient if components are to be manufactured in large numbers. For quality production, to maintain the size within tolerable limits, gauges are used. They are made with high accuracy, are quick and easy to use.

forged steel and ground to the required limits. Shape of the gauge depends upon the shape of the object and dimension, which is being measured. Different

Fig. 19.14

GO and NOT GO Plug Gauge

Fig. 19.15

GO and NOT GO Gauge

CAD 19.15

PUTTING TOLERANCES USING CAD

Values of tolerances (both upper and lower) are set in the New Dimension Style dialog box shown in Fig. 19.16. To get this dialog box follow the steps given below: A. On menu bar, click Dimension and then from the pull down menu, select Dimension Style…. B. Dimension Style Manager is displayed. Click New… button on right side.

Part D – Chapter 19

388

C. Create New Dimension style dialog box is displayed. Type the name of new style in the text box and click Continue button at the bottom. New Dimension Style dialog box is displayed. (Fig. 19.16).

Fig. 19.16

Dimension Style Dialog Box for Tolerances

D. Click the last tab Tolerances in this dialog box. Its tolerance format tile has the following six combo boxes:

A. Method required. Meaning of each is explained below: (i) None (ii) Symmetrical (iii) Deviation

(iv) Limits

(v) Basic

No tolerance is placed. Adds a plus/minus single tolerance value Enter a tolerance value in the Upper value edit box. Adds different or same plus/minus tolerance values. A (+) symbol precedes the tolerance value entered in the Upper value edit box and a (–) symbol precedes the tolerance value entered in the Lower value edit box. (see Fig. 19.S6) Actual values of the upper and the lower limits It displays a maximum and a minimum value, one over the other. The maximum value is the dimension value plus the value entered in the Upper value edit box. The minimum value is the dimension value minus the value entered in the Lower value edit box. Draws a rectangle around the basic dimension and no tolerance is given.

Tolerances, Limits and Fits

389

B. Precision

C. Upper Value Method selected is ‘Symmetrical’, AutoCAD uses this value for both the tolerances.

D. Lower Value Type here the minimum or the lower tolerance value.

E. Scaling for Height Specify a scale factor for the fraction text to the main dimension text. AutoCAD calculates the tolerance height.

F. Vertical Position

Top Aligns the tolerance text with the top of the main dimension value. Middle Aligns the tolerance text with middle of the main dimension value. Bottom Aligns the tolerance text with the bottom of the main dimension value.

E. In the Tolerance alignment tile click any radio button as desired. F. In the Zero suppression tile, click any check box as required. Example 15

Figure 19.S15 shows a drawing. Put the dimensions in a style given below:

Aim This tutorial demonstrates the use of dimensions with tolerances.

Solution Open a New

15

Symmetrical ±

35

1

Basic

0.

Command: DDIM

Limits 30.2 29.9

50

Create a drawing of the size as shown in Fig. 19.S6 at any suitable position with the basic dimensions. Then follow the steps given below for dimensioning. tions, Symmetrical and Basic. So four dimension styles have to be created, named and then used. 1. First set the style of dimensions.

15

Ø 18 ± 0.1

45° ± 0°

+ 0.1 Type the command and press Enter. 65 – 0.1 Dimension Style Manager dialog box appears. Click Deviation New button. Fig. 19.S15 Tutorial on Dimensions Create New Dimension Style dialog box appears. with Tolerances Assign a style name as Style Limits. Click Continue. New Dimension style dialog box appears (Fig. 19.16). Click on the Tolerance tab. Make the following settings (shown bold) if the default values shown in the dialog box are different than the desired ones (Refer Fig. 19.16):

Part D – Chapter 19

390

In the Tolerance Format tile set as under: Method: Precision Upper value: Vertical position

Limits 0.0 0.2 0.1 Middle

Click OK button and then the Close button. The dialog box disappears and the drawing appears again. dimension is placed as shown in the Fig. 19.S6. Style Dev. Choose the Method as Deviation. Set both the upper and the lower tolerance values as 0.1. 5. Repeat Step 3 and dimension the bottom horizontal line. Note that the tolerances are not in the same format as put in Step 3. Style Sym’ but choose the Method as Symmetrical and set both the tolerances as 0.1. 7. Click on Align option on the Dimension pull down menu to dimension the inclined line. Click on the ends of inclined line and put the dimension at a suitable distance. 9. Click the Angular option on the Dimension pull down menu and specify the angle of the inclined line w.r.t. the horizontal line. Style Basic. Choose the Method as Basic. 11. Repeat step 3 and dimension the left vertical line. Note: Following system variables can be used to make the settings for the Method of putting tolerances and tolerance values. These settings can be used at the command prompt instead of the Dimension Style dialog box. Dimlim To put the tolerances on or off. Dimtp Dimtm Dimtolj To justify tolerances vertically. Dimtfac To specify ratio of the tolerance text height in relation to the dimension text height.

TIP To put different tolerances on the same drawing, any one of the following methods can be followed: a. Set the system variables as mentioned above. b. Create a new dimension style with different name for a set of tolerances. c. Put a tolerance and then modify by the dimension tolerances. First select the dimension, then click Modify on Menu bar and choose Properties on pull down menu. Scroll the list down to tolerances and modify the values of the tolerances.

THEORY QUESTIONS

Tolerances, Limits and Fits

CAD

VIVA-VOCE QUESTIONS 1. Differentiate between ‘basic size’ and ‘actual size’.

MULTIPLE CHOICE QUESTIONS Tick the correct answer 1. Difference between basic and actual size is called (a) Fit (c) deviation (a) (b) (c) (d)

(b) tolerance (d) gap

dimensional difference between the maximum limit of mating parts difference between basic and actual size difference between upper and lower deviation difference between basic size of hole and actual size of shaft

(a) a letter symbol (c) both by a letter symbol and a number symbol 4. Upper case letters for tolerance is used for (a) shaft (c) hole

(b) a number symbol (d) a three digit number

(c) equal on both + and – sides of any IT value 6. Tolerance value on a drawing depends upon (a) method of manufacturing (c) skill of operator

(d) none of these

(a) (b) (c) (d)

maximum shaft diameter and maximum hole size minimum shaft diameter and minimum hole size minimum shaft diameter and maximum hole size maximum shaft diameter and minimum hole size

(b) journal (d) both for hole and shaft

(b) number of parts to be manufactured (d) function of the part

391

Part D – Chapter 19

392

CAD 9. Method of putting tolerances of a dimension is set in dimension dialog box using (a) Text tab (b) Units tab (c) Fit tab (d) Tolerance tab 10. Tolerances are put on a drawing using AutoCAD by

(c) put basic size, upper and lower values all at one time (d) tolerances cannot be put 11. Text size of tolerance value is (a) of the same size as the basic size (b) 50% more than basic size ze (d) can be set to any size

ANSWERS

ASSIGNMENT

ON

TO

MULTIPLE CHOICE QUESTIONS

TOLERANCES, LIMITS

AND

FITS

1. A hole of 50 mm has tolerance as C10. Calculate its maximum and minimum sizes. 3. A shaft of diameter 30 mm rotates at medium speed in a sleeve bearing. Specify the following: Maximum and minimum shaft diameters Maximum and minimum sleeve inside diameters 4. A gusset plate shown in Fig. 19.P1 is to be Specify suitable tolerances. 5. tity. Specify suitable tolerances for the 55 mm end and for overall Fig. 19.P1 length. 6. A stepped block is shown in Fig. 19.P3. Evaluate tolerance for size A.

Fig. 19.P2

A Stepped Shaft

Fig. 19.P3

A Gusset Plate

A Stepped Block

Tolerances, Limits and Fits

CAD ASSIGNMENT

ON

TOLERANCES, LIMITS

393 AND

FITS

of + 0.5 and – 0.3.

Fig. 19.P4 9. Draw Fig. 19.P5 and put the tolerances as tabulated below: Size

Basic size

A

Upper deviation

deviation

0.03

0.01

B

Method Deviation Symmetrical

C

50

0.04

D

30

0.04

Deviation

Also calculate the tolerances for the dimensions X and Y.

HOMEWORK

(c) Key in the keyway of a pulley dismantled frequently (d) Ball bearing on a shaft 11. Name the sizes A, B ... F for a shaft shown in Fig. 19.P6.

13. Calculate limits of the shaft diameter having fundamental tolerance as

Fig. 19.P5

Part D – Chapter 19

394

14. Evaluate sizes and tolerances for dimensions A and B shown in Fig. 19.P7.

Fig. 19.P6

Fig. 19.P7

(a) 55 H11-c11

(b) 65 H7-k6

(c) 75 H7-s6

16.

PROBLEMS

FOR

PRACTICE

(a) Maximum and minimum clearance between the mating parts. (b) Fundamental deviations of both the parts.

(a) Shaft diameter limits (c) Bush outside diameter limits

(b) Bush hole diameter limits (d) Housing hole diameter limits

eye end (B). Find the following: (b) Maximu and minimum size of pin.

Fig. 19.P9

Fig. 19.P8

Fig. 19.P10

20 20.1

Geometrical Tolerances and Surface Finish

INTRODUCTION

For example, straight line means straightness, circle means that the

Fig. 20.1

20.2

Geometric Shape Variations

TYPES OF TOLERANCES

A. Size Tolerances

B. Form Tolerances

C. Position Tolerances

required and the other is the maximum error which can thin circle showing the zone within which the actual

Fig. 20.2

Types of Tolerances

Part D – Chapter 20

396

20.3 20.3.1

TERMINOLOGY Geometric Tolerance -

20.3.2

Tolerance Zone

a component must be contained -

20.3.3

Feature

20.3.4

Axis

20.3.5

Median

20.3.6

Boxed Dimensions

Fig. 20.3 Tolerance Zone

Ø

20.4

FRAME

drawing call out

Geometrical Tolerances and Surface Finish

Fig. 20.4

20.5

397

A Frame and Its Contents

DATUM

20.5.1

Datum Feature

20.5.2

Datum Triangle -

Fig. 20.5

20.5.3

Representation of a Datum

Datum Letter

Fig. 20.6

Datum Triangle and Datum Letters

Part D – Chapter 20

398

20.5.4

Multi-datums

Fig. 20.7

20.6

20.6.1

Multiple Datums

MATERIAL CONDITION

Maximum Material Condition (MMC)

bonus tolerance

20.6.2

Least Material Condition (LMC)

Geometrical Tolerances and Surface Finish

20.6.3

20.7

Regardless of Feature Size (S)

TOLERANCE SYMBOL

A. Single Feature Tolerances B. Related Features Tolerances

Fig. 20.8

Geometric Tolerance Symbols and Their Proportions

399

Part D – Chapter 20

400

C. Runout Tolerances

20.8

TOLERANCE VALUE

20.9

INDICATING GEOMETRICAL TOLERANCES ON DRAWINGS

Geometrical tolerances are put on a drawing in a frame

outline axis or median plane of the part, it is terminated on the extension lines datum features

leader line

Fig. 20.9 Indicating Tolerances on a Drawing

length datum is far off axis of datum feature

Fig. 20.10

20.10 20.10.1

Indicating Datum on a Drawing

FORM TOLERANCE FOR SINGLE FEATURES Straightness

Geometrical Tolerances and Surface Finish

Fig. 20.11

20.10.2

401

Indicating Straightness on a Drawing

Flatness

planes enclosing the actual surface at the low-

20.10.3

Circularity

Fig. 20.13

20.10.4

Fig. 20.12

Indicating Flatness on a Drawing

Indicating Circularity on a Drawing

Cylindricity -

Fig. 20.14

Indicating Cylindricity on a Drawing

Part D – Chapter 20

402

20.10.5

-

20.10.6 Fig. 20.15 a Line on a Drawing

Fig. 20.16

20.11

20.11.1

TOLERANCES ON RELATED FEATURES

Parallelism -

Fig. 20.17

Indicating Parallelism of a Surface on a Drawing

Geometrical Tolerances and Surface Finish

20.11.2

403

Perpendicularity -

Fig. 20.18

20.11.3

Indicating Perpendicularity of a Surface on Drawing

Angularity -

-

Fig. 20.19

20.11.4

Concentricity

Indicating Angularity of Surface on a Drawing

Part D – Chapter 20

404

Fig. 20.20

20.11.5

Indicating Tolerance for Concentricity on a Drawing

Symmetry

Fig. 20.21

20.11.6

Indicating Tolerance for Symmetry on a Drawing

Position

-

Fig. 20.22

20.11.7

Indicating Tolerance for Position on a Drawing

Position Tolerance for Patterns

Geometrical Tolerances and Surface Finish

Fig. 20.23

405

Tolerance for Pattern

For such situations, two tolerances are and the other for feature location as shown

20.12 20.12.1

RUN OUT Circular Run Out

Fig. 20.24

Tolerance for Pattern and Feature

change in its reading noted for one full turn of the part without changing the axial position of the dial

Fig. 20.25

20.12.2

Total Run Out

Indicating Circular Run Out on a Drawing

Part D – Chapter 20

406

Fig. 20.26

Indicating Total Run Out on a Drawing

Example 1

Fig. 20.S1A

Solution

Fig. 20.S1B

Fig. 20.S1C

Fig. 20.S1D

Example 2

Solution

Fig. 20.S2A

Example 3

Fig. 20.S2B

Geometrical Tolerances and Surface Finish

Fig. 20.S3 Head size

407

An Inspection Gauge Pin size

Solution

-

Table 20.S3 Head size

Example 4

Allowable values of tolerance Pin size

Part D – Chapter 20

408 Solution

Fig. 20.S4A

Fig. 20.S4B

Fig. 20.S4C

Example 5

Fig. 20.S5A

Fig. 20.S5B

Soluion Example 6

Fig. 20.S6A

Solution Example 7

Solution

Fig. 20.S6B

Geometrical Tolerances and Surface Finish

Fig. 20.S7

Interpretaions of Drawing Callouts

Fig. 20.S8

409

A Jig Plate

Example 8

Solution

mm

20.13

SURFACE TEXTURE

-

Roughness

Roughness width Roughness height Roughness cut-off

Waviness

Fig. 20.27

Surface Texture

Part D – Chapter 20

410 Waviness height Waviness width Lay Flaws

20.14

PROFILES

20.14.1

20.14.2

20.14.3

Fig. 20.28 Related to a Surface

20.14.4

20.14.5

Peak to Valley Height

20.14.6

Mean Roughness Index (Ra)

hn

20.15

SURFACE ROUGHNESS NUMBER -

Geometrical Tolerances and Surface Finish

,h

20.16

411

n

ROUGHNESS SYMBOLS basic symbol for

surface roughness has two legs;

Where: a1 b d f

– Maximum permissible roughness – Production method – Direction of lay – Roughness criterion other than Ra

a2 – Minimum permissible roughness c – Sampling length e – Machining allowance

Fig. 20.29

Basic a circle

Part D – Chapter 20

412

Table 20.1

Roughness symbols and their meanings

Geometrical Tolerances and Surface Finish

20.17

413

LAY -

Table 20.2

20.18

Symbols used for direction of lay

ROUGHNESS GRADE NUMBER AND GRADE SYMBOLS

Part D – Chapter 20

414 Table 20.3

20.19

ROUGHNESS WITH MANUFACTURING PROCESSES

Table 20.4 S.No.

Roughness grades and grade symbols

Range of roughness obtainable with different processes

Process

Minimum– Maximum

Average application range Minimum–Maximum

Gas cutting

5 Forging 8 Milling Filing

Electric discharge machining Electron beam

(Contd.)

Geometrical Tolerances and Surface Finish Table 20.4 S.No.

Process

415

(Contd.)

Minimum– Maximum

Average application range Minimum–Maximum

Extruding

Electro-chemical machining

Electro polish

20.20

ROUGHNESS FOR TYPICAL APPLICATIONS

Table 20.5 Roughness in microns

Applications and suggested roughness Applications

(Contd.)

Part D – Chapter 20

416

Table 20.5 Roughness in microns

20.21

(Contd.) Applications

RULES FOR PUTTING ROUGHNESS SYMBOLS

-

Fig. 20.30

Roughness Symbol Orientation and Placement

Geometrical Tolerances and Surface Finish

417

Example 9

Fig. 20.S9A

A Stepped Block

Solution -

Fig. 20.S9B

Fig. 20.S9C

Part D – Chapter 20

418

Fig. 20.S9D

Fig. 20.S9E

CAD 20.22

GEOMETRIC TOLERANCES Annotate tab of the ribbon, in the Dimension Tolerance Menu bar Dimension and from the pull down Command line TOLERANCE or TOL

arrow Tolerance…

dialog box named Geometric Tolerance -

Sym tile on left upper corner, Symbol Fig. 20.31

Geometric Tolerance Dialog Box

tile labeled Sym Tolerance 1

tolerance value calls for the Fig. 20.32

Tolerance Symbols

Geometrical Tolerances and Surface Finish Datum 1 tile or Datum 2 Enter tolerance location:

419 OK

Click at the desired location on the screen. Complete frame is placed at

Example 10

Solution Geometric tolerance

TOL

Symbol dialog box

Sym

Fig. 20.S10

Tolerance 1

tolerance value Material Condition M Datum OK

A

THEORY QUESTIONS

CAD

VIVA-VOCE QUESTIONS

A Feature Control Frame

420

Part D – Chapter 20

MULTIPLE CHOICE QUESTIONS

CAD

Geometrical Tolerances and Surface Finish

ANSWERS

ASSIGNMENT

ON

TO

421

MULTIPLE CHOICE QUESTIONS

GEOMETRIC TOLERANCES

AND

SURFACE ROUGHNESS

Fig. 20.P1

Fig. 20.P2

m m m

Part D – Chapter 20

422

Fig. 20.P3

CAD ASSIGNMENT

ON

Fig. 20.P4

GEOMETRIC TOLERANCES ROUGHNESS

AND

A Slider

SURFACE

HOMEWORK

Fig. 20.P5

9.

Fig. 20.P6

Fig. 20.P7

A V Block

Geometrical Tolerances and Surface Finish

PROBLEMS

Fig. 20.P8

Fig. 20.P10

FOR

PRACTICE

Fig. 20.P9

Fig. 20.P11

Feature diameter in mm

Fig. 20.P12 15. Datum for pin

423

tolerance

Part D – Chapter 20

424 Datum for ring

Fig. 20.P13

Vertical hole on a lathe

Fig. 20.P14

A Bearing Support

Fig. 20.P15

21 21.1

INTRODUCTION

material properties

21.2

TYPES OF ENGINEERING MATERIALS

Part D – Chapter 21

426

21.3

FERROUS METALS Wrought iron

Fig. 21.1

21.3.1

Name of Ferrous Metals with Percentage of Carbon

Carbon Steels Carbon

steel plates

427 bars pipes

A. Low Carbon Steel

2

2

2

B. Medium Carbon Steel 2 2

2

C. High Carbon Steel applications

Table 21.1 % Carbon

21.3.2

Cast Iron

A. Ductile Cast Iron

2

Applications of plain carbon steels Applications

Part D – Chapter 21

428

B. Grey Cast Iron 2

C. White Cast Iron

D. Malleable Cast Iron

2

Ferritic

Table 21.2 Type

21.3.3

Pearlitic

Applications of cast irons Applications

Alloy Steels

2

2

2

Table 21.3 Alloying element

Alloying elements, properties imparted and applications Properties imparted/Applications

Lead

(Contd.)

429 Table 21.3 Alloying element

21.3.4

(Contd.)

Properties imparted/Applications

Stainless Steels

A. Austinitic Stainless Steels

B. Ferritic Stainless Steels

C. Martensitic Stainless Steels

Table 21.4 Stainless Steel Type

Applications of stainless steels Application

Austenitic

21.4

DESIGNATION OF STEELS [IS 1762–1974 Part 1]

Part D – Chapter 21

430

21.4.1

Steel Designation According to Mechanical Properties

Fe

E

NNN

CHS

2

Chemical symbols Special characteristics Application symbol

21.4.2

Special Characteristics Codes

Code B – Resistance to Brittle fracture

Code D – Formability (for sheets only)

Code F – Surface Finish (for sheets only)

Code P – Purity code for steel

Code Q – Steel Quality code

Code S – Surface condition code

Code T – Treatment code

SC

AS tensile strength yield strength no strength

431

Code W – Weldability code

Other character codes

Examples 2 2

2

21.5 STEEL DESIGNATION ACCORDING TO CHEMICAL COMPOSITION [IS 7598–1974] 21.5.1

Unalloyed Steels

NN

C or T

MM

G

or

Examples

21.5.2

Alloy Steels

A. Low and Medium Alloy Steels

NN

A1

N1

A2

N2

A3

N3

SC

Part D – Chapter 21

432

carbon

4 10 100

Example

B. High Alloy Steels X X

NN A1

P1

A2

P2

A3

P3

SC

carbon

Example

C. Tool Steels XT code is put instead XT Example

NN A1

P1 A2

P2

A3 P3

SC

433

21.6

CODE DESIGNATION FOR FERROUS CASTINGS [IS 4863–1968] mechanical properties

chemical

composition

TC

NN

2

Examples 2 2

chemical composition

GS

A1

P1

A2

P2

A3

P3

Example

21.7

NON-FERROUS METALS

Table 21.5 Metal/Alloy

Non-ferrous metals and applications

Characteristics

Applications

(Contd.)

Part D – Chapter 21

434

Table 21.5 Metal/Alloy

(Contd.)

Characteristics

Applications

Lead

corrosion resistance

wires

corrosion resistance

corrosion resistance

21.7.1

Copper Alloys

435

Table 21.6

Copper and its alloys

Copper alloy and composition

21.7.2

Applications

Code Designation for Copper and Its Alloys [IS 2378 – 1974]

MM CC AI SF

G GX e

Manufacturing Method (MM) GC h f

GD d

T

GW

Part D – Chapter 21

436

Chemical Composition (CC) CATH ETP FRHC Alloy Index (AI) up to 1%, only symbol percentage Surface Finish (SF) J

more than 1,

J7

O

H

J8

symbol

MC

T

Example

21.7.3

Aluminum Alloys

Table 21.7 Aluminum alloy

21.7.4

Aluminum and its alloys Applications

Code Designation for Aluminum and its Alloys [IS 6051 – 1970]

437 Example

21.8

21.8.1

PLASTICS

Thermoplastics

Table 21.8 Thermoplastics

Properties and uses of thermoplastics

Characteristics

Applications

Contd.

Part D – Chapter 21

438

Table 21.8 Thermoplastics

21.8.2

Characteristics

(Cond.) Applications

Thermoset Plastics

Table 21.9 Thermoplastics

Properties and uses of thermoset plastics

Characteristics

Applications

Urea is used for radio

(Contd.)

439

Table 21.9 Thermoplastics

21.8.3

Characteristics

Elastomers (Rubber)

in mechanical cellular Mechanical rubber Cellular rubber Open cell

Closed cell

21.8.4

21.9

Wood

BILL OF MATERIALS

(Contd.) Applications

Part D – Chapter 21

440

Table 21.10 S.No.

Item

1

Bill of materials

Description Ø 30

Materal

1

300

2

Quantity

1

8

3

2

4

4

30

5

4

6

1

7

1

Example 1

Solution Table 21.S1 Item

Materials for some items Suitale material

Gear Knife (Contd.)

441 Table 21.S1 Item

(Contd.) Suitale material

Example 2 Solution Table 21.S2

Codes of some materials

Material details

Code

2 2

2 2

2

4300

Part D – Chapter 21

442

CAD 21.10

TABLE COMMAND Home TABLE

Fig. 21.2

Table style Insertion options Insertion behavior

Columns & Rows

Set cell style

Insert Table Dialog Box

ribbon

Annotation

443

Command: TABLE Specify insertion point:

Type TABLE and press Enter key. Click a point for the upper left corner of the table.

Example 3

Solution Table style Insertion options Insertion behavior Columns & Rows

Set cell style

Fig. 21.S3

21.11

BLOCK ATTRIBUTES

invisible

A Blank Table

444

Part D – Chapter 21

THEORY QUESTIONS

CAD

VIVA-VOCE QUESTIONS

MULTIPLE CHOICE QUESTIONS

445

CAD

ANSWERS

TO

MULTIPLE CHOICE QUESTIONS

22 22.1

Production Drawings

INTRODUCTION

A production drawing is an authorized document to produce a part in the workshop. Mentioning tolerances,

22.2

TITLE BLOCK

Fig. 22.1

A Title Block used in Industry

Prtodution Drawings

22.3

447

MANUFACTURING PROCESSES

c. Joining processes

Arc welding, Gas welding, Spot welding, Seam welding, Brazing, -

-

22.3.1

Casting Processes

A. Sand Casting machining allowance, etc.

B. Die Casting -

22.3.2

Forming Processes

A. Forging -

B. Rolling

Part D – Chapter 22

448

C. Drawing deep drawing using

D. Extrusion

ment is high.

22.3.3

Joining Processes

A. Arc Welding -

B. Gas Welding

C. Spot Welding

D. Seam Welding

Prtodution Drawings

E. Brazing copper alloy

F. Soldering

G. Riveting

22.3.4

Material Removal Processes

machines

22.3.5

Chemical Processes

A. Electric Discharge Machine (EDM)

B. Electro-Chemical Machining (ECM)

C. Etching

449

Part D – Chapter 22

450

D. Electroplating

22.3.6

Surface Finishing Processes

a. Surface grinding Cylindrical grinding c. Centerless grinding d. Internal grinder is used to grind internal holes. e. Honing Lapping

. to

g. Painting

22.3.7

22.4

CNC Machines

HEAT TREATMENT PROCESSES -

A. Hardening -

B. Tempering -

Prtodution Drawings

451

C. Annealing -

D. Normalizing

22.5

TOOLING

22.5.1 According to tool material According to cutting points According to cutting action

22.5.2

Tool Angles

22.5.3

Cutting Speed Fig. 22.2

tool and work piece. It depends upon material higher cutting speed and greater top rake angle.

Lathe Tool Cutting Angles

Part D – Chapter 22

452

22.5.4

Tools Used for Different Machines

A. Lathe

B. Shaper -

C. Milling

Fig. 22.3

Fig. 22.4

Lathe Tools

Milling Cutter

D. Vertical Milling

E. Drilling Machine

-

Prtodution Drawings

Fig. 22.5

Milling Cutters

453

Fig. 22.6

Types of Drills

F. Slotting Machine tool.

G. Broaching Machine

a small material. Initial teeth called roughing

Fig. 22.7

Broaching Tool

H. Hobbing Machine

the gear.

I. Planing Machine Fig. 22.8

Hob Cutter

Part D – Chapter 22

454

22.6

INSPECTION

-

is to check hole size tolerances, Ring gauge Pneumatic gauges

Comparators

22.7

JIGS

a. Support and Hold Guide

cutting tool

jig for drilling

Plug gauge Snap gauge has

Prtodution Drawings

455

Fig. 22.9 A Jig for Drilling Holes in a Chain Link

Example 1 Example 1 Solution

Fig. 22.10

22.8

A Jig for Drilling Holes at an Angle

FIXTURES only holds the work and does

NOT guide any tool

Part D – Chapter 22

456

Fig. 22.11

22.9

A Fixture on a Lathe

ASSEMBLY DRAWINGS -

Fig. 22.12

An Assembly Drawing with Part Numbers

Table 22.1 Part No.

Part Name

Part list for the drill vice Material

Jaws Screw

Mild steel

Handle

Mild steel

Handle stop

Mild steel

Quantity

Prtodution Drawings

22.10

457

STANDARD MECHANICAL COMPONENTS

Table 22.2 Standard component

IS number

Designation of standard components Designation

Meaning

with nut nut and lock nut with nut and lock nut

Plain washers

screws

Allen head screws

length Studs

(Contd.)

Part D – Chapter 22

458

Table 22.2 Standard component

IS number

(Contd.)

Designation

Meaning

Splines

Solid or Split

Oil seal

Oil seal

22.11

PRODUCTION DRAWING -

22.12

PROCESS SHEET

Prtodution Drawings 1

4

3

2

459 5

6

0.01 A +0.02

13 –0

10

A

A

Ø 50 A

Ø 90 Ø 25 D7

3 B

6h7

B

20 C

C

36° 23 Modern Engineering Company Drawing no. 123

Identification no. Pulley/23

Material: cast iron

D

Sheet no.1 Scale full size

Tolerance ± 0.04

V - groove pulley

Surface finish 25

Drawn by

Date

Checked by

Date

Approved by

1

3

2

Fig. 22.13

4

D

Date

5

6

Production Drawing of a V Grooved Pulley

work centers work place or machines which are mentioned in the process sheet. Example 2

Solution Table 22.S2

Process sheet for a V groove pulley

Description of work Drawing Number Material Operation No.

Number required Cycle time Pulley diameter Machine

Operation

Tool/gauge

Time—minutes

Inspect the casting

Set compound slide (Contd.)

Part D – Chapter 22

460

Table 22.S2 Operation No.

Machine

(Contd.)

Operation

Tool/gauge

Set compound slide

Boring tool

Broaching

22.13

Broach

TITLE BLOCK File

Scroll down and select ISO A3 Named Plot Styles

New Open

Alternately Command : MVSETUP Enable paper space? [No/Yes] : Enter an option [Align/Create/Scale viewports/Options/Title block/Undo] : T Enter title block option [Delete objects/Origin/Undo/Insert] : I

Time—minutes

Prtodution Drawings

Fig. 22.14

ISO A3 Template

THEORY QUESTIONS

CAD

VIVA-VOCE QUESTIONS

461

462

Part D – Chapter 22

MULTIPLE CHOICE QUESTIONS

Prtodution Drawings

463

15. A production drawing has

ANSWERS

TO

ASSIGNMENT

MULTIPLE CHOICE QUESTIONS

ON

PRODUCTION DRAWINGS -

Fig. 22.P1

Flange of a Coupling

Fig. 22.P3

Fig. 22.P2

Cylinder and Liner

Half Sleeve Bearing

464

Part D – Chapter 22

CAD ASSIGNMENT ON PRODUCTION DRAWINGS -

Fig. 22.P4

Cylinder and Piston

production details and prepare a process sheet.

Fig. 22.P5

Taper Sleeve

Fig. 22.P6

Bearing Block

Prtodution Drawings

PROBLEMS FOR PRACTICE 7.

Fig. 22.P7

Shaft and Flange

8.

it.

Fig. 22.P8

Piston and Gudgeon Pin

465

Part E

MACHINE PARTS

23 23.1

Springs

INTRODUCTION

its original position. They are used for example in automobiles to absorb the road shocks. Spring is used in a spring balance to measure the load. It can also be used to keep any machine element pressed or stretched and many other applications. Springs are available in many shapes and each has a typical application.

23.2

CLASSIFICATION

Tension spring Compression spring Spiral spring

It gets elongated when load is applied. It gets compressed when load is applied. It gets twisted when load is applied.

Helical spring Leaf spring Torsion spring

The wire is wound in a helical fashion (Fig. 23.1). Rectangular strips of steel are bent in the shape of an arc and joined together (Fig. 23.8). A thin steel strip is wound in a spiral form (Fig. 23.9).

Diaphragm spring

A steel disk bent in the shape of a saucer (Fig. 23.11).

23.3

HELICAL SPRING

Helical springs are made of steel wire (generally circular in cross-section) bent in a helical form. The different terms used with these springs are (Refer Fig. 23.1): Wire diameter (d) Diameter of the wire with which a spring is made. Coil diameter (D) Mean diameter of the helical coil. Outside diameter Coil diameter plus wire diameter. Inside diameter Coil diameter minus wire diameter. Number of turns (n) Number of complete turn of the coils in a spring. Pitch (p) Axial distance between centers of two adjacent coils.

Springs

467

Helix angle ( ) Free length (FL) Solid length (SL)

Angle which the coil makes with a line normal to axis of spring. Total axial length between two extreme coils without load. Total axial length between two extreme coils when fully compressed.

Shape of ends

The ends may be open, closed or ground (Fig. 23.2).

23.3.1

Compression Spring

A compression spring is just a coil wound in helical fashion (Fig. 23.1A). The visible side of the wire is shown at the helix angle ( ). The rear portion of the coil is visible partially, as it is covered by front coils. The rear coils are also inclined at same helix angle but are opposite to the front coils. If the spring wire is circular, it To draw a compression spring of circular wire, draw a center line and then draw semicircles (having curvature opposite to center line) of given number of turns (n) and radius (d/2) at a distance of coil radius (D/2) from the center line, spaced at a distance of (p). Draw another set of semicircles facing opposite to the previously drawn semicircles but displaced axially by a distance (p/2). Join the semi-circular arcs by inclined lines. Then draw the lines for the rear side of the spring as shown in Fig. 23.1. The ends may be terminated at the center line after desired number of coils. The other view of the spring is just two circles of outside diameter If the number of turns are large, drawing of spring may be time consuming and laborious. Drawing of such a spring can be represented by a few turns at the ends and then the middle turns can be just by straight dashed lines. (See Figure 23.10)

Fig. 23.1

A Helical Compression Spring

Fig. 23.2

Ends of a Compression Spring

If the outside diameter of all coils remains constant, it is called a cylindrical helix or generally only helical spring. If the diameter changes along the axis, it is called conical helix. It is shown in

Part E – Chapter 23

468 a. Open b. Closed c. Ground

23.3.2

Gap between the last and adjacent coil remains the same as the pitch (Fig. 23.2A) The extreme ends are pressed to touch the adjacent coil so that there is no gap there (Fig. 23.2B). The ends are ground on a grinding machine to make them square with its axis (Fig. 23.2C).

Tension Spring

These are drawn in the same way as the compression spring, but the pitch of the coil is same as wire diameter, i.e. p = d and hence all the coils touch each other on sides. Since there is no gap between the coils hence the rear portion of the spring is not visible (Fig. 23.3)

Fig. 23.3

A Tension Spring (Full Loop End)

Fig. 23.4

Ends of a Tension Spring (Half Loop End)

Type of ends used for tension spring are different than compression spring. Two types of ends are used for these springs: full loop and half loop. A full loop end is circular (Fig. 23.3) while half loop is semicircular with smooth curvature with the coils (Fig. 23.4)

23.3.3

Torsion Spring

These springs are wound either with closed coils, i.e. no gap between the coils similar to tension springs or shown in Fig. 23.5. Load is applied at right angles to the axis so as to twist the coil. For these springs, stiffits free position. Some of the torsion springs are made dual, i.e. left half has LHS coils and right half has RHS coils. In addition to two ends, there is a third radial extension of the spring (Fig. 23.6). The torque is applied in the center while the extreme free ends take the reaction.

Fig. 23.5

A Torsion Spring

Fig. 23.6

A Dual Torsion Spring

Springs

23.4

469

LEAF SPRING

A leaf spring is made of rectangular steel strips of different lengths (called leaves) clamped together in lengths The length, cross-section and number of strips depend upon the load to be supported. The topmost leaf has applications. Leaves are kept in their position by a center bolt and clamps along the length to keep leaves below each other and do not allow the leaves to rotate.

23.4.1

Shapes of Leaf Springs

A leaf spring can have many shapes like quarter elliptical, semi-elliptical, three quarter elliptical and full elliptical

A. are supported and load is applied at the center. Its use can be seen in most of the heavy duty vehicles for rear suspension of the wheels.

B. Two semi-elliptical springs are joined together end to end to form an elliptical shape (Fig. 23.8B). This com-

Fig. 23.7

Components of a Leaf Spring

470

Part E – Chapter 23

C. This shape is just half of the semi-elliptical spring. That is why it is called quarter elliptical spring. One end has an eye end and the leaves are clamped in the center (Fig. 23.8C).

D. It is a combination of semi-elliptical and quarter elliptical to form a three quarter ellptical spring. It is shown in (Fig. 23.8D).

Fig. 23.8

Shapes of Leaf Springs

These springs are used to store torsional energy, e.g. winding of a watch or clock. A steel strip is wound in the form of a spiral (Fig. 23.9). One end is curved to take the reaction and torque is applied at the central end which is straight.

23.4.2

Drawing a Leaf Spring

Following dimensions should be known for drawing a leaf spring: Radius of curvature Number of leaves Length of each leaf Width and thickness of leaves Number of clamps Shape of ends If ends are circular then center to center distance between the eyes and eye diameter To draw a leaf spring, adopt the following method: 1. Draw center line of the spring and mark centers of the eye ends at right angles to this axis. 2. Draw a circle at the center of the eye end of eye diameter. Make another concentric circle for the eye ends at distance equal to the thickness of the leaf. 3. Open compass equal to radius of curvature and set its center on the center line such that it is tangential to the circles of the eye. 4. With the same center but radius increased by leaf thickness every time, draw arcs of decreasing lengths for given number of leaves. 5. Draw the center bolt and clamps at the appropriate places.

Fig. 23.9

Torsional Spring

Springs

23.5

471

CONVENTIONAL AND SYMBOLIC REPRESENTATION OF SPRINGS

On drawings where the number of springs is large, drawing a spring in its actual shape is too much time consuming and laborious. Hence springs are shown either conventionally or symbolically. The wire is represented just be a line inclined at helix angle. Conventions followed to draw a compression spring (A), a tension spring (B), torsion spring (C) and a leaf spring (D) are shown in Fig. 23.10.

Fig. 23.10

23.6

Symbolic Representations of Springs

DIAPHRAGM SPRING

These are made of thin steel disk having conical shape. It is also called Belleville spring. It stores energy when pressed axially. It may be an annular disk as shown in Fig. 23.11A or with radial slots diameter, cone angle and thickness of the disk.

Fig. 23.11

Diaphragm Springs

Part E – Chapter 23

472

CAD AutoCAD can be helpful in drawing a spring. Draw only one coil of a helical spring and rest can be copied Example 1 Draw a helical coil compression spring of 8 turns for a wire diameter of 5 mm and a coil diameter of 30 mm. The gap between the coils is 5 mm.

Solution Wire diameter is 5 mm and gap between coils is 5 hence pitch = 5 + 5 = 10 mm. 1. Draw a vertical center line of 80-mm length as length of spring (8 10).

3. 4.

5. 6.

7.

lines at distance of 15 mm (half the coil diameter) on each side of the center line. (Fig. 23.S1A). At the lower end of the left line draw a circle of 2.5 mm radius (half the wire diameter). Copy this circle at two more points using COPY command. Use the base point of circle as center of the circle and second point as @30,5 and for the other circle as @0,10. Using Tangent object snap draw lines 1-3, 2-4, 3-5 and 4-6 (Fig. 23.S1B) Using TRIM command trim these circles. Select the boundary for trimming as these inclined lines and object to trim as the circle Fig. 23.S1 on the inner side within the lines as shown in Fig. 23.S1B. Trim the lines 3-5 and 4-6 also using TRIM command.

Drawing a Helical Spring Using CAD

9. Use ARRAY command to complete the spring. Specify the data as under:

Row offset - 10 (5 mm gap between wires and 5 mm as wire diameter)

Figure 23.S1C is displayed as a coil spring.

23.7

HELIX COMMAND

twist in Counter Clock-Wise direction (CCW). To have clockwise direction type W for the twist and specify CW for clockwise direction. base radius About the height of spring, You can specify either ‘turn Height’ of one turn or by specifying ‘Axis end point’ for the total length of the spring. Use of this command is explained in the example 2.

Springs Example 2

473

Draw a helical coil compression spring of 8 turns for a wire diameter of 5 mm and coil

it in magenta color.

Solution 1. Set Color. Command: color

Type the command and press Enter key

2. Draw Helix. Command: Helix Number of turns = 3.0000 Twist=CCW Specify center point of base: Specify base radius or [Diameter] : 15 Specify top radius or [Diameter] : Specify helix height or [Axis endpoint/Turns turn Height/tWist] : T Enter number of turns : 8 Specify helix height or [Axis endpoint/Turns /turn Height/tWist] : H Specify distance between turns : 10

Type the command and press Enter key Displays default values Click anywhere on screen Specify base radius as 15 Press Enter to accept shown radius Type T to specify number of turns Specify 8 turns and press Enter key Type H to specify height of a turn Specify the height of one turn

3. Change Viewing Direction from Top View to (1,1,1). Command: VPOINT Current view direction: VIEWDIR=0.0000,0.0000,1.0000 Specify a view point or [Rotate] : 1,1,1

4. Draw a Circle of Wire Diameter as 5 mm. Command: CIRCLE Specify center point for circle or [3P/2P/Ttr Set object snap on by pressing F3 key. (tan tan radius)]: Click at the bottom end of the helix. Specify radius of circle or [Diameter]: 2.5

5. Sweeping the Circle along the Helix. Command: SWEEP Select objects to sweep: Select objects to sweep: Select sweep path or [Alignment/ Base point/Scale/Twist]:

Click on the circle

Click on the helix.

6. Shade the Spring. Command: SHADE

Try the following: 1. The same example by specifying 8-mm top radius to draw a conical spring. 2. The same example by specifying a square instead of a circle to draw a spring with square wire.

Fig. 23.S2

A Helical Spring

Part E – Chapter 23

474

Example 3 Draw 6 turns of V threads for pitch circle diameter as 30 mm and pitch as 5 mm. Shade it in green color as shown in Fig. 3.S3.

Solution 1. Set color. Command: color Select color dialog box is displayed.

Type the command and press Enter key

2. Draw Helix. Command: Helix Number of turns = 3.0000 Twist = CCW Specify center point of base: 0,0,0 Specify base radius or [Diameter] : 15 Specify top radius or [Diameter] : Specify helix height or [Axis endpoint/Turns/ turn Height/tWist] : T Enter number of turns : 6 Specify helix height or [Axis endpoint/Turns/ turn Height/tWist] : H Specify distance between turns : 5

Type coordinates as origin Specify radius as 15 Press Enter to accept radius shown Type T to specify number of turns Specify 6 turns and press Enter key Type H to specify height of a turn

3. Change Viewing Direction from Top View to (1,1,1). Command: VPOINT Specify a view point or [Rotate] : 1,1,1

4. Shift UCS to Bottom End of the Coil. On View tab of the ribbon, in Coordinates panel, click on origin UCS icon, when AutoCAD prompts for: Specify new origin point : Click at the bottom end of the coil. 5. Rotate UCS to bring XY plane at right angle to coil. On the same panel click on Y-axis rotate icon and specify rotation angle -90°. 6. Then again click on rotate X axis rotate icon and specify angle 90°. Now the UCS position 7. Draw a triangle of one side as 5 mm. Command: POLYGON Enter number of sides : 3 Specify center of polygon or [Edge]: E Specify second endpoint of edge: @5,0

Specify number of sides as 3 Type E to choose Edge option Click at the bottom end of spring Specify coordinates of the other edge

8. Sweeping the triangle along the helix. Command: SWEEP Select objects to sweep: Select objects to sweep:

Click on the triangle Press Enter key

Fig. 23.S3

6 Turns of V Threads

Springs Select sweep path or [Alignment/Base point /Scale/Twist]:

475

Click on the helix

9. Change viewing direction. On Views tab and on Views panel, click the Views button with downwards arrow. Choose Left view 10. Shade the threads. Command: SHADE

Try to draw other type of threads.

THEORY QUESTIONS 1. Classify the springs. Differentiate between conventional and symbolic representation of a spring 2. What is meant by ends of springs? Describe the various ends used for compression type coil spring with sketches. 3. What are the parameters deciding the stiffness of a leaf spring? 4. What is a torsion spring? Give two examples of any type by sketches. 5. Differentiate between coil and diaphragm spring.

CAD 6. Describe the method to draw a compression type helical spring using CAD. 7. How can a leaf spring be drawn using CAD? 9. How can the direction of twist of a helical spring can be changed to clockwise?

VIVA-VOCE QUESTIONS 1. What is the function of a spring? 2. What are the various types of coils springs? Differentiate between each type. 3. Differentiate between a coil and a leaf spring.

MULTIPLE CHOICE QUESTIONS 1. A spring is used to (a) act as energy reservoir (c) to take load 2. Material for a leaf spring is (a) cast iron (c) spring steel 3. Stiffness of a spring remains (a) always constant

(b) support vibrating parts (d) for all mentioned in a, b and c (b) mild steel (d) aluminum (b) always varies

Part E – Chapter 23

476

4. Cross-section of material for a leaf spring is (a) rectangular (b) circular (c) square (d) thin plate 5. Shape of a diaphragm spring is like (a) circular disk (b) saucer (c) spiral (d) helical 6. Generally gap between coil of a tension type coil spring is (a) equal to wire diameter (b) two times the wire diameter (c) 1.5 times the wire diameter (d) no gap 7. Solid length of a helical compression spring is when (a) wire used for spring is solid circular (b) gap between two coils is zero (c) inside diameter is zero (d) there is no load on the spring

ANSWERS 1. (d) 7. (b)

2. (c)

TO

MULTIPLE CHOICE QUESTONS

3. (c)

ASSIGNMENT

4. (a)

ON

5. (b)

6. (d)

SPRINGS

1. Draw two views of a compression type coil spring with the following data: Wire diameter = 8 mm Coil diameter = 80 mm Pitch = 15 mm Number of turns = 7 Type of ends is square 2. A semi-elliptical spring has 6 leaves of size 100 6 mm cross-section. Its master leaf has circular eye ends of radius 15 mm. Center to center distance between the eyes is 1000 mm and radius of curvature is 1200 mm. All leaves are joined with a center bolt of 15 mm diameter of a suitable length. Four clamps are used (2 on each side) at equal distance made of 50

CAD ASSIGNMENT

ON

SPRINGS

3. Draw two views of a tension type coil spring with the following data Wire diameter = 5 mm Coil diameter = 60 mm Number of turns = 12 Type of ends as full loop 4. Draw a full elliptical spring for the data given in question 2 above. Hint: their lengths. Use MIRROR comand to copy semi-elliptical to full elliptical spring.

Springs

477

HOMEWORK 5. Draw a torsion leaf spring with the following data Strip size 25 1 mm Number of turns 10 Starting radius 20 mm Central end straight of straight length 30 mm and Last turn with an eye end of radius 5 mm 6. Draw a diaphragm spring of outside diameter 200 mm, inside diameter 80 mm, thickness 1.5 mm, 8 radial slots of width 10 mm and cone angle 160 degrees. Assume a suitable length of T.

PROBLEMS

FOR

PRACTICE

7. Draw two views of a conical helical compression type coil spring with the following data Wire diameter = 10 mm Coil diameter at base = 100 mm Coil diameter at top = 50 mm Pitch = 18 mm Number of turns = 12 Type of ends is ground 10 mm (10 mm along its axis) with the following data Coil diameter at bottom 80 mm Coil diameter at top 40 mm Pitch 12 mm Number of turns 8 Type of ends open

24 24.1

Belts and Pulleys

INTRODUCTION

In machines, mechanical power is transmitted from one component to another depending upon the requirement. Various types of power transmission systems are available. Important ones are belt and pulleys, gears (Chapter 26), etc.

24.2

BELTS

Belts are used for power transmission from one pulley to another. If the direction of rotation of the driver and driven is same, the open belt arrangement is used (Fig. 24.1A). One side of the belt is called tight side while the other is called slack side. Tight side should be kept at bottom. Sometimes an idler is used inside or outside the belt to keep the belt tight over the pulleys (Fig. 24.1B). If the direction of rotation of the driven is opposite to the driver, then crossed belt arrangement is used (Fig. 24.1C). If the axes of the driver and driven are at 90°, the arrangement is shown in Fig. 24.1D. Center distance between the pulleys has to be long for this arrangement.

Fig. 24.1

Belt Arrangements

Belts with rectangular cross-section are called Flat belts (Section 24.2.1). V shaped belts are called V belts (Section 24.2.2). In olden days a rope of circular cross-section was also used (Section 24.2.3).

24.2.1

Flat Belts

These are low cost and can run on small pulleys. They have a tendency to slip and hence need high tension These are made of leather, fabric, rubberized fabric, non-reinforced rubber/plastic, reinforced leather, etc. Flat belts are of three types:

Belts and Pulleys

479

A. Plain Flat Plain Flat belts are of rectangular cross-section with no teeth or groove (Fig. 24.2A).

B. Grooved or Serrated Grooved or Serrated belts have longitudinal grooves of V section adjacent to each other made on the inside periphery of the belt (Fig. 24.2B). The power transmission capacity increases due to wedge formed by V groove. Sometimes they are also called poly V belts.

C. Toothed Belts Toothed belts similar size of teeth on the pulley. They are used for positive drive, e.g. cam shaft of an engine.

Fig. 24.2 Types of Flat Belts

24.2.2

V Belts [IS 2494 (1974)]

V belts are most commonly used in industry. These are available in large variety of standard sizes and types. nance. Best speed for operation for belts is between 8 to 30 m/s. Ideal speed for standard belt is 23 m/s and V belts are made in two sizes; conventional and narrow. Conventional belts are designated as A, B, C, D and E. Width and thickness of these belts is shown in Fig. 24.3 while the angle for all is 40°. More than one belts are used to increase power transmission capacity. Number of belts on one pulley should not be more than eight. If the number is more than eight, then larger section should be chosen. Narrow belts are designated as

Fig. 24.3

V Belt Cross-Sections

V belts are designated by its cross-section letter A, B, etc. followed by inside length. For example A1262 means a belt with cross-section as A and inside length 1262. Table 24.1 shows the sizes of various belts and the range of inside length (minimum to maximum).

Part E – Chapter 24

480

Table 24.1 Width

6

Height

24.2.3

24.3

10

13

17

22

32

38

6

8

11

14

19

23

3

4 212

296

420

832

2303

3230

860

1262

1916

2820

6332

18063

18080

Min. length Max. length

8

Size of V belts

Ropes

PULLEYS

They are used to transmit power with the help of belts. A pulley is a circular machine element hav(Fig. 24.4A). For a grooved pulley, the number of grooves can be one or more than one (Fig. 24.4B). The belt allows a certain amount of slip and hence they do not transmit positive power (no slip). Toothed belts use a transmission.

Fig. 24.4

Various Types of Pulleys

Small pulleys can be made of forged steel, but large pulleys are made of Cast Iron. Aluminum pulleys are used where light construction is required. The rim is connected to the hub either by a solid disk or spokes for large diameter pulley. The solid disk is sometimes provided with a web between hub and rim with holes to reduce weight of the pulley.

24.4

TYPES OF PULLEYS

A. According to shape: Grooved (Section 24.6) B. According to driving belt: Flat belt – The belt is of rectangular section. Single V belt – A single belt having 40° angle called as V belt is used (Section 24.6.1).

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Multi V belt – Many V belts are used in parallel for more power transmission (Section 24.6.2). Toothed belt – It has teeth on the inside periphery and is used for positive drive (Section 24.7). Rope – A circular rope is used (Section 24.8). C. According to construction:

D. According to use:

Idler pulley – Does not transmit power. Generally used for providing belt tension.

24.5

FLAT BELT PULLEYS

convex (Fig. 24.4A). This helps in keeping the belt positioned centrally on the pulley. Flat pulleys are of many types, e.g. solid, webbed, straight armed, curved armed, built up, stepped, fast and loose. Each type is described in the following sections.

24.5.1

Solid Pulley

24.5.2

Webbed Pulley

Medium sized pulleys are made webbed to reduce weight and save material (Fig. 24.6). Sometimes the web is provided with holes to deerease weight and save material.

Fig. 24.5

Solid Pulley

Fig. 24.6

Webbed Pulley

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24.5.3

Armed Pulley

Large sized pulleys have a rim and arms joining the rim and central portion called the hub. The arms can be straight (Fig. 24.7A) or curved (Fig. 24.7B). Number of arms can be 4, 6 or more depending upon the size of pulley. Crosssection of the arm is generally elliptical but can be circular. The hub has hole and keyway to suit the shaft size.

Fig. 24.7A

24.5.4

Straight Arms

Fig. 24.7B

Curved Arms

Built Up Pulley

Very big pulleys are made as built up type. Both hub and rim are made in two halves and then joined together with bolts and nuts (Fig. 24.8). Hub and rim are provided with radial holes. Arms are of circular cross-section with outer end having a collar and step at one end and inner end is stepped. Inner ends of the rods are shrunk rod is riveted to the rim. The rim halves are joined by a curved strap on the inside periphery of the rim. The strap is riveted to one side of the rim using counter sunk rivets and bolted by a counter sunk bolt at the other side. The two halves of hub are bolted on shaft with a key in between.

Fig. 24.8

Built up Pulley

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24.5.5

483

Stepped Pulley

With stepped pulleys, speed of the driven pulley can be changed by changing the position of belt from one step to another step. The steps are generally three or four (Fig. 24.9). More than four are not commonly used. The pulleys are so arranged that the belt at smallest step of the driver aligns with biggest step of driven pulley. Their sizes are so adjusted that the belt length required remains same.

24.5.6

Fast and Loose Pulley

Sometimes two pulleys are adjacent to each other. One of the pulleys is keyed to the shaft called fast pulley, while the other is without key called loose pulley. Loose pulley runs freely on a bush without transmitting power to shaft. This arrangement is known as Fast and Loose pulley (Fig. 24.10). Whenever the power transmission is not required, belt is made to slip from fast to loose pulley. Some machine tools use this type of power transmission to connect and disconnect power as required.

Fig. 24.9

Fig. 24.10

Stepped Pulley

Fast and Loose Pulley

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24.6

GROOVED PULLEYS

Grooved pulleys use V belts. These belts have a standard cross-section A, B, C, D and E. The section to be selected depends upon the power to be transmitted. Section A is for less power and E for larger power. If the power to be transmitted is more than the capacity of one belt, two or more belts can be used in parallel. Table 24.2 gives minimum size and preferred diameter of the pulley required for different size of belts. Table 24.2 Cross-section

Belt cross-sections and Pulley diameters (mm) Minimum pulley diameter

Preferred diameter

A B

140

C D E

700

Although the angle of the belt is 40°, but the angle of pulley groove is made lesser than 40°, so that the wedging action causes more gripping force between pulley and belt. Driver pulleys (generally smaller) have included angle between 32° and 34° and large pulley 36° and 38°. Depth of the groove is also kept about 10% more than the actual depth of belt so that when the belt gets compressed due to continuous use, it may not touch the bottom surface of the groove, else the wedging action will not take place. Grooved pulleys can have one groove or more than one if more power is to be transmitted.

24.6.1

Single Belt Grooved Pulley

Only one V belt is used (Fig. 24.11). It may be solid or belts due to wedging action of the belt into the groove.

24.6.2

Multi Belt Grooved Pulley

Many V grooves are cut adjacent to each other (Fig. 24.12). Outer wall thickness is kept slightly more than inner wall thickness. The gap between grooves depends upon the material also. Larger size of pulleys are webbed and holes are also made to make them light. Fig. 24.11

24.6.3

Single Belt Groove Pulley

Stepped Grooved Pulley

Purpose of stepped grooved pulle in pair, aligned such that belt of smallest pulley aligns with biggest pulley. Angle of groove is kept between 34° and 38° (Fig. 24.13). The groove is kept deeper than the height of belt. Size of groove depends upon cross-section of belt A, B or C. The pulley shown in Fig. 24.13 is for B belt.

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Fig. 24.12

Fig. 24.13

24.7

485

Multi Belt Groove Pulley

Stepped Pulley for V Belts

TOOTHED PULLEY

Their use is limited to applications where slip may affect the performance of the machine. The outer periphery use can be seen for cam shaft drive in I.C. engines. A collar is provided on the sides of driver to keep the belt within the width of the pulley, which may shift on side due to slight mis-alignment of shafts.

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Fig. 24.14

24.8

Toothed Pulley

ROPE PULLEY

They are not commonly used. Very large pulleys may use this type of drive. A rope of circular cross-section is Two grooves are adjacent to each other for more power transmission.

Fig. 24.15

Rope Pulley

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CAD 24.9

AUTOLISP

It is a programming language which comes with AutoCAD. It can create drawings using a program written in this language. It is similar to any other language and can perform conditional branching using IF command. It can perform repeated looping actions like any other language. Aim of this section is not to teach this language but just appraise the powers of AutoCAD using this language. It is very useful where the shape remains same and only the size changes. For such situations, the variables can be assigned to varying dimensions and then changing the values of these variables will automatically create a drawing according to new dimensions. An idea of AutoLISP is given in Example 1.

24.9.1

CREATING AN AUTOLISP PROGRAM

This is demonstrated by Example 1. Example 1

Write a program to draw the following:

center (100,100) as shown in Fig. 24.S1A, One rectangle centrally inside the circles, A line joining the diagonal corners of the rectangle, and Text ‘My First Program’ above the outer circle.

Solution 1. AutoLISP program is written in windows notepad and NOT in MS word. To open note pad, click Start at left bottom corner of screen and then click in the following sequence. Start

Programs

Accessories

Notepad

2. Start typing the program exactly as shown below. This program is to give results as shown in Fig. 24.S1A. Fig. 24.S2 shows the various names assigned to variables used in the program. Be very careful about syntax tion of the program is given at the end of the program.

Fig. 24.S1A

Fig. 24.S1B

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(defun C:C1() ; This function draws two circles one rectangle, one line and a line of text in different colors (graphscr) ;feed input data (setq x 100) (setq y 80) (setq r 40) (setq cen (list x y)) (setq cr1 ‘(80 60)) (setq cr2 ‘(120 100)) ; ;Use AutoCAD commands ;Draw circles with Circle command (command “color” “Red”) (command “circle” cen r) (setq r (+ r 15)) (command “color” 4 ) (command “circle” cen r) (command “color” 5) ; ;Using Rectangle command (command “Rectangle” cr1 cr2) ; ;Using LIne command (command “Line” cr1 cr2 “”) ; ;Using text command (setq h 6) (setq ang 0) (setq sp ‘(55 140)) (setq txt "My First Program") (command "Text“ sp h ang txt) ; (prompt "Congratulations") (terpri) (prompt "Thanks") )

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3. Save the program with the name Tut1.lsp in any folder. Explanation of the Program It may be noted that each instruction is written within parenthesis. The number of opening parentheses has to be equal to closing parentheses. If there is a difference of one, an error message 1> appears while executing the program. The meaning of each line is given below in RHS in italics. (defun C1() A function starts with an opening parenthesis ( Defun

; This function draws two circles one rectangle, one line and a line of text in different colors

comment line and does not take ;feed input data (graphscr) (setq x 100)

Setq

(setq y 100) (setq r 40) (setq cen (list x y))

list command to specify a center

(setq cr1 ‘(80 60)) (setq cr2 ‘(120 100)) ; ;Use AutoCAD commands ;Draw circles with Circle command (command “color” “red”)

l

command -

(command “circle” cen r) (setq r (+ r 15)) (command “color” 4) (command “circle” cen r) ; ;Using Rectangle command (command “color” 5) (command “Rectangle” cr1 cr2) ; ;Using LIne command (command “Line” cr1 cr2 “”)

. ; ;Using text command (setq h 6)

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490 (setq ang 0) (setq sp ‘(55 140)) (setq txt “My First Program”) (command “Text” sp h ang txt) (prompt “Congratulations”) (terpri)

\n”

(prompt “Thanks”) )

24.9.2

Loading an Autolisp Program

Start AutoCAD program. On the menu bar, click Tools and in the pull down menu click on Load Application…. Load/Unload dialog box appears. In the Look in combo box, click the arrow on RHS and select the folder where the Lisp program is saved. A list of programs is shown in the window below it. Choose the name of the program. Name of File name text box. Click Load button. Click Close button at the bottom of the dialog box. A message appears at the command line that the program is successfully loaded.

24.9.3

Executing the Program

is created by the program automatically as shown in Fig. 24.S1A.

24.10

SPECIFYING VARIABLES

Setq command. To make it user interactive, these have to be supplied at the prompts to make it interactive. Autolisp permits different types of variables, e.g, integer variable, real variables, string variables. It also uses List variables, which is like a subscripted array. For example: (setq a 23) (setq b 23.4) (setq c “Joun”)

Assigns an integer value 23 to variable a Assigns a real value (with decimal point) 23.4 to variable b Assigns a string value (text) to variable c list variable d. Note the parentheses.

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491

EXTRACTING DATA FROM LIST VARIABLE

List function contains many values in it. These values can be extracted by the Car, Cadr, Caddr and Cdr commands. There are more commands but only important ones are described here. Use of these commands is shown below by example: e Extracts of list and assigns its value to p, i.e., p Extracts second item of list and assigns its value to , i.e., = 6 Extracts third item of list and assigns its value to r, i.e., r = 7 Extracts and assign its value to another list s, i.e., s = ( 6 7 8 9)

(setq p Car (list e)) (setq q Cadr (list e)) (setq r Caddr (list e)) (setq s Cdr (list e))

24.12

GET COMMNADS

There are many GET commands like getangle, getcorner, getint, getpoint, getreal, etc. to get values from the user interactively either from screen by mouse or from the command line using key board. Only a few are described below: Getpoint is used to get the coordinates of click of mouse on the screen. The prompt within quotes guides the user. Its use is shown below, in which coordinates of a variable P is assigned same wherever the mouse is clicked. (Setq P (getpoint “Pick a point on screen ”))

Getdist command is used to get a value from the command line. Example below shows to feed the data is assigned to variable d in the expression below: (setq d (getdist “Specify distance ”))

24.13

MATHEMATICAL OPERATIONS

Mathematical operations like addition, subtraction, multiplication, division, etc., can be done on variables as tabulated below: Operation

Use of operator

What it does

Addition

(Setq a (+ n1 n2 n3))

(n1+ n2 + n3) value is assigned to a variable a

Subtraction

(Setq (– n1 n2))

(n1– n2) value is assigned to a variable

Multiplication

(Setq c (* n1 n2))

(n1* n2) value is assigned to a variable c

Division

(Setq d (/ n1 n2))

(n1/ n2) value is assigned to a variable d

Operations like sqrt, log, expt (raise to power), cos, sin, tan, abs, etc. can also be performed. Refer an AutoLISP book for details of these operators.

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24.14

ANGLES IN AUTOLISP

Angles used by Autolisp have to be in radians only while AutoCAD by default takes in degrees. Angle com-

(Setq theta (angle p1 p2))

to radians. Name of the function is dtr. A value supplied through parenthesis will be converted to degrees. (defun dtr (a) (* pi (/ a 180.0) )

Polar command is used to get relative coordinates of a point p2 for a given angle and distance from another point p1. Its syntax is (setq p2 (polar p1 ang1 dist1))

The above instruction calculates and assigns coordinates of p2 with respect to p1 for given angle stored in variable name ang1 and distance in variable name dist1.

24.15

LOGICAL OPERATORS

Variables can be compared by logical operators like equal to (=), greater than (>), less than (=), lesser than and equal to (