Plan and Organization for a Bolt, Nut, And Rivet Plant in Bombay, India

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PLAN AND ORGANIZATION FOR A

BOLT, NUT, AND RIVET PLANT

IN BOMBAY, INDIA

THESIS Submitted in Partial Fulfillment of the requirements for the degree of MASTER OF MECHANICAL ENGINEERING at the POLYTECHNIC INSTITUTE OF BROOKLYN by H. C. Keskar May 19^0

Approved:

Thesis Advisor

Head of

A

ProQuest Number: 27591397

All rights reserved INFORMATION TO ALL USERS The q u a lity of this re p ro d u c tio n is d e p e n d e n t u p o n the q u a lity of the co p y su b m itte d . In the unlikely e v e n t that the a u th o r did not send a c o m p le te m a n u scrip t and there are missing p a g e s, these will be n o te d . Also, if m a te ria l had to be re m o v e d , a n o te will in d ic a te the d e le tio n .

uest P roQ uest 27591397 Published by ProQuest LLO (2019). C o p y rig h t of the Dissertation is held by the A uthor. All rights reserved. This work is p ro te cte d a g a in s t u n a u th o rize d co p yin g under Title 17, United States C o d e M icroform Edition © ProQuest LLO. ProQuest LLO. 789 East Eisenhower Parkway P.Q. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346

-dL—

VITA

I was born on the 26th day of the month of August 1922 , in Poona, a city about 100 miles from Bombay, India.

Having passed the Matriculation

Examination of the Bombay University in the year 1938, I joined the Ram Narain Ruia College in Bombay to proceed with my studies in Science. There I passed the Intermediate Examination in Science of the Bombay Uni­ versity in 19W.

I was then admitted to the Engineering College, Benares

Hindu University, Benares, India, and there I obtained my Degree

Bach­

elor of Science (Engineering) in Mechanical and Electrical Engineering in the year 19l4 i. "While in the Engineering College, I had to undergo apprenticeship in the Bombay Electric Supply and Tramways Company, Ltd., Bombay, for a peri­ od of six months.

Immediately after completing college, I was enç)loyed as

a Trainee Supervisor in the Bharat Tool Manufacturing Company, Bombay, a firm engaged in the manufacture of taps, dies, reamers, drills, etc. After working there for a few months I got a job in the Department of Mi­ nitions Production operated by the Government of India, as a Technical Assistant.

I worked there for two years and then joined the Bombay Munic­

ipal Water Works Department, first as Inspector (Mechanical) and then as Assistant Engineer.

rJhile in the Water Works Department I was given the

job of installing a floating pumping station of UO million gallons per day capacity on pontoons.

This also required the installation of a poTrerhouse,

workshop, and other auxiliary installations. In the meanwhile, I was selected by the Bombay Government for higher studies in Mechanical Engineering abroad.

I proceeded to the United States

-ii-

in August 19U8 and joined the Polytechnic Institute of Brooklyn in the fall term of 19U8 . I hope to complete my studies as Master of Mechanical Engineering in June, 1950 . I have devoted a period of eight months to the completion of this thesis. Respectfully, l~2ES.

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product

SPECIFICATIONS

In this section complete scientific analyses of the technical fea­ tures of the products under consideration are presented.

The specifica­

tions are stated in the form of technical and engineering data, describ­ ing the characteristics of the products.

They represent British and

American standard types. BRITISH STANDARD IHITWORTH SPECIFICATIONS (BOLTS, NUTS AND WASHERS) General The dimensions of the British Ihitworth black bolts, nuts and washers shall be in accordance ivith the Table on page 38, Nominal Size The diameters of bolts given in column 1 of the Table in this speci­ fication shall be considered the nominal size of the unthreaded portion of the bolt. Screw Threads The screw threads will be in accordance Tiith column 2 of the Table. T&dth Across Flats The width across flats shall be in accordance with columns 3 and h of Table 8 of this specification. In cases where smaller width across flats than that of B. S. W. is required by the purchaser, it shall be the next smaller B. 8 . W. bolt size and corresponding tolerances given in Table ^ shall apply. The width across flat for B. S. square bolt heads and nuts shall be the same for hexagonal bolt head and nuts.

-

311-

Length of Screwed Part of Bolts The length of the screwed part for bolts up to and including l-l/l}." in length shall be 1 -1 /2 times the diameter of the bolt; for bolts above l-l/L" and up to 8 " in length, twice the diameter of bolt; and for bolts above 8 ", two and one-half times the diameter of bolt. Washers The dimensions of, B. S. black washers shall be as given in columns 10 to 1^ of the Table.

-3?-

Bolts, Regular The dimensions of American standard regular bolt heads and nuts are as given in Table 7 on

page 32.,

The width across flats of all bolt heads is 1-1/2 D adjusted to six­ teenths of an inch, where D = diameter of bolt, except for sizes of l/L" to 5/8” inclusive, of finished bolt heads.

For these bolts, the width

across flats is (1-1/2 D / l/l6 ) adjusted to sixteenths. The tolerance for width across flats is as follows : Unfinished and semi-finished -

0.050 D from basic ] (.0,015 / 0.006)from basic

Finished bolt heads -

The minimum width across rounded comers of square bolt heads is: Unfinished and semi-finished -

1.373 x min. mdth across flats

The minimum width across rounded corners of hexagon bolt heads is: Unfinished, semi-finished and finished hexagon bolt heads l.lU X min. width across flats Ihe nominal height of head is the distance from the top to the bear­ ing surface. For unfinished bolts it is 2/3 D adjusted to fractions and for finished bolt heads it is 3/U D. For semi-finished bolt heads it is as follows: Size in inches -

l/h to ?/l6

1/2 to 7/8

1 to 1-7/8

Height -

2/3 D -l/6h

2/3 D -1/32

2/3 D -l/l6

These values are adjusted to the nearest l/6i| inch, with a tolerance of / (0.016 D / 0 .012 ) from the nominal. finished bolt heads.

This is the tolerance for un­

For finishedbolt heads it is £ (0.0l5 D / O.OO3 ).

The tops of all the heads are flat and chamfered at an angle to the top

-36surfaoe of 2$ degrees for square and 30 degrees for hexagon.

The diam-

eter of the top flat circle is maximum width across flats. Nomenclature : Unfinished -

Not machined on any surface.

Semi-finished - Machined under head only. Finished -

Machined on all surfaces.

In the project under consideration, the production Td.ll mostly con­ sist of unfinished and semi-finished bolts.

Dfuts

American standard nuts are classified as regular and jam nuts and are further classified as unfinished, semi-finished and finished nuts. Unfinished nuts are threaded but are not machined on any surface.

Semi­

finished nuts are threadedand are machined on the bearing surface only. Finished nuts are threadedand machined on all surfaces. The width across flats of all types of nuts is 1-1/2 D, except for sizes l/U" to 5/8" where

width across flats equals 1-1/2

D

/l/l6with a

tolerance of minus 0.050 D from basic for unfinished and semi-finished nuts and of (0.0l5 / 0.006) from basic for finished nuts. Minimum width across comers is the sameas for bolt heads.

The nominal thickness is

the overall distance from the top to the bearing surface for unfinished and finished nuts. For semi-finished nuts, it is as follows: Size in inches -

l/h to 7/l6

1/2 to 1-1/8

1-l/U to 2-l/j|

Thickness -

1/2 D / l/6k

1/2 D / 3/6L

1/2 D / 1/Ï6

For the project under consideration, the production will mostly con-sist of unfinished and semi-finished nuts.

-37Washers The dimensions of washers manufactured will be as per Table 9A? on page 1^0 . Rivets The rivets

Trill

be manufactured according to sizes given on the

sketch on pageipL •

The folloTdng Tables, 9 and 9A

, and the drawings of small rivets

and large rivets complement the American Standard Specifications so far discussed.

-38-

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SECTION FOUR

THE PROCESSES AND OPERATIONS REQUIRED IN MAKING BOLTS, NUTS, RIVETS, AND WASHERS

-U 2 -

Section Four INTRODUCTORY SURVEY OF THE MANUFACTURING PROCESSES AND MATERIAL SPECIFICATIONS PROPOSED FOR APPLICATION The methods employed in the manufacture of the bolts, nuts and rivets under consideration shall, as far as possible^^be the latest and as efficient as possible without sacrificing the economy of production. The operations will be more or less semi-automatic, making possible the use of labor which is not highly skilled. Bolts Sizes l/U" to 3/U"

-

^Manufactured on cold heading machines. îhreads either cut, or rolled.

Sizes above 3/U"xip to 1-1/2"

-

Manufactured on heavy-duty hot forging machines. Threads are cut.

Nuts

Sizes up to 1/2"dia.

-

Cold pressed.

Sizes above 1/2"dia.

-

Hot pressed.

All nuts tapped on automatic and semi-automatic tapping machines. Washers All plate washers cold punched. Rivets All rivets will be cold formed on cold heading machines.

-U 3 -

Material Specifications For all cold working purposesj^ the wire used will be open hearth, basic steeli^ and bright drawn.

It will be of a low carbon content with

the following specifications: Carbon

- O.lU to 0.20^

Manganese

- 0.30 to 0.U5#

Silicon

-About 0.1^

Phosphorus

)

Sulphur

)

Under O.OU# The ordinary tolerances for drawing wire will be £ 0.002 inches. For the manufacture of heavy bolts, nuts and rivets^ the steel used will be SAE 1010 to 1065. The physical properties of the materials mentioned above are: (1)

Tensile strength

- U5,000 to 55,000

(2) Minimum yield point - Half the tensile strength.

THE PROCESSES AND OPERATIONS REQUIRED IN MAKING BOLTS, NUTS, RIVETS AND WASHERS IN DETAIL The technique of manufacture of the various products with special reference to operation analysis is presented from now on in detail. The methods of manufacture adopted for the plant under consideration are intended to be modem, and aimed at low costs. Manufacture of Bolts The manufacture of bolts may be classified under two headings^ namely (a)

Cold forged

-UU— (b) Hot forged It is conmion practice in the United States to produce bolts up to 3/U" diameter on cold headers.

Bolts over 3/U" diameter and over 8" long

are made by the hot forging method in heavy-duty heading and forging ma­ chines. Single Stroke Headers The plastic deformation of

metal wire or ofrods without the use of

heat has found its greatest field ofapplication in the formation of heads in the bolt and rivet industry. known as cold heading.

Consequently, the process has come to be

The process is sometimes performed in a standard

punch press, but the individual handling of pre-cut blanks is slow and re­ duces the rate of production. For this reason, there hasbeen developed a line of special machines^ known as "cold headers".

Theseare, in effect, horizontal presses ar­

ranged for continuous^fast operation, with automatic feed and cutoff. Standard machines are designed for single, double, triple, or multi­ ple stroke, and are either solid-die or open-die types.

The single stroke

requires one revolution of the flywheel to produce a part; the double stroke requires two revolutions; the triple stroke, three revolutions. The multiple-blow header is a special type machdjie which makes a part at each revolution but requires several consecutive stations to perform work. These machines may be driven directly by their own motors,or by belts taking the power from the counter shaft.

Some smaller short-stroke ma­

chines make use of a toggle mechanism, and possess the advantage of having the toggle operate alternatively above and below the center, thus produc­

—ii.5-

ing two blows for each revolution of the flyrfheel, and giving double the output of a conventional machine. The type of header to be used for a particular job depends on the amount of material needed to form the upset, the length of the shank, and the location and shape of head.

In general practice, it is not advisable

to form a head mth a diameter in excess of 2-l/U times the diameter of the stroke on the single blow machine, but there is no hard and fast rule. Standard Design Formulae for Bolt Head and Rivet Head Formation

CoT*t has

D - Diameter of ?ri.re S - Length of shank L - Length of wire to form head For single stroke - L 2-l/h D For double stroke - L ii-l/2 D For triple stroke - L 6 to 8 D Special lengths up to 12 D are possible, but for lengths over 8 D, the speed of the machine must be reduced by 20^ to avoid too much diffi­ culty in clearing the Tjork from the dies. In an open-die header the length ”S^’ should not be less than ^ D or

—ii.6—

a reasonable thickness to withstand heading pressure, # Solid and Open-Dies for Gold Forming Solid dies are simple cylinders of hardened tool steel with a hole for the shank of the work piece, Open-dies are made from two rectangular blocks with send-circular grooves on each of four sides.

(See Fig?agey% )

Other factors being equal, solid dies are generally preferred^ as their use eliminates the possibility of producing a flash under the head or down the shank. However, if the shank is less than I/I6 ", trouble may be experienced because of lack of rigidity in the knock-out pin, and spec­ ial precautions may have to be taken in setting up the dies. Header Capacity and Working The capacity of a header is usually designated by the diameter of the wire to be used; this rating also refers to the power required for such«r Standard articles as cap and machine screws with head sizes according to ‘ American Standards. Whitworth heads, however, may require larger headers because of the greater amount of material to be upset.

The volume, and

particularly the area of the upset, really define the tonnage required,

and from this the proper size of the machine may be selected. A thin head of considerable area requires much more pressure than a thick head of conparatively smaller diameter although the volume of the metal may be alike in both upsets. Single stroke machines are adequate when head diameters or volume are relatively small, and the material lends itself easily to upsetting. The sketches shown illustrate the point;

-47

DIES FOR COLD FORMING

O PEN

I>IE

-k8-

\~ 7

Double stroke headers are necessary when the diameter of the head is more than 2-l/h shank diameter, or when the volume of metal is greater than can be upset in a single blow machine. Such examoles are illustrated below:

Q Triple stroke machines are required to produce large heads of the type shown below, in which a considerable Quantity of stock must be gathered.

Steps involved are: 1.

r

Cutoff

2. First coning 3. U

=

Second coning

D U. Finished head Single Stroke Header Operating

On a single stroke solid die machine, the ware stock is passed through automatic feed rolls and into a cutoff die.

At the start of the

stroke the wire feeds foiaTardj^until it comes against a positive stop ad­ justed to the required length of the blank.

A shear blade then slides

-k9~ across the face of the die and cuts off the projecting piece of the stock. The blade hs.s a semi-circular notch in its cutting edge into which the blank is held by springs or a hinged finger.

As the stroke continues,

the blade carries the blank forward, until it is directly in line ?n.th the heading die and holds it in that position^until the punch forces it into the die. draws.

The finger or springs then release and the cutoff slide withThe punch pushes the blanlc back into the die until its movement

is arrested by the knock-out pin, where upon the outer end of the blank is compressed^and forced to conform to the shape of the cavity in the punch head or the end of the die.

*

With this arrangement it is obvious that parts having the same diam­ eter head and shank, but different lengths, can be made vdLth the same set of tools by merely adjusting the position of the stock and knock-out pin within the limits of the machine. At the start of the stroke the entire pressure exerted by the punch must be absorbed by the knock-out pin, but in the moment when the stock begins to upset, the tht^st is taken largely by the newly formed shoulder against the face of the die, and pressure on the pin is reduced.

There

is thus only a limited tendency for the shank to swell and bind in the die; neither is there much possibility of squaring up the end by pressure against the pin. For this reason it is particularly inportant that the cutoff be as clean and square as possible.

If the stock is draggedover in shearing,

the unequal distribution of metal at the head end willproduce lopsided heads, while the shank end may require a secondary pointing operation to

-50-

produce a product of acceptable appearance. In the open-die type machine, the stock feeds through a cut-off die until it reaches the stock stop.

The header die opens slightly to permit

free passage of the stock. A powerful clamping mechanism then closes the header die to grip the stock, and at the same time slides the die over to the center of the machine, shearing off the blank and holding it in line with the advancing punch.

Thvnst of-the punch is resisted partly by the

gripping action of the dies and partly by a backup plate over which the die slides.

On the return stroke the die carries the finished part back

to the feed position where it is automatically opened so that the incom­ ing stock can eject the part. The travel of the die is only slightly greater than the diameter of the stock;*and as these machines usually operate at high speeds,'-the stock stop can be timed to strike the headed part as it leaves the die and kick it clear of the advancing punch. As the back face of the die is used as a shear, it is apparent that each different length of the bolt or rivet Td.ll require its own set of dies, and while this may not be important for very long runs, it can add appreciably to the cost of short runs.

There is, moreover, considerable

danger of chipping the rear edge of the die and thus ruining it long be­ fore its working life is expended. Mu],tiple Stroke Headers In operation, double and triple stroke machines of the solid, open^ and universal types are identical ivith their single stroke counter part, except that on completion of the first stroke, the feed and ejector mech-

—51—

anism remains inoperative, and a second punch is presented to work with the next stroke of the machine. On triple stroke machines, this is followed by a third punch before the work cycle repeats. The method of indexing the punches varies Td.th the different machine makes.

On one type the punch holder moves upward a fixed distance i,?ith

each successive stroke, and is locked in position.

On another type the

punch holder moves horizontally instead of vertically; and on another, the punch holder is caused, to oscillate through an arc, with positive stops used to insure exact alignment. For special purposes, other attachments may be added to standard ma­ chines.

In addition to heading, it is possible to perform a certain

amount of extrusion.

On bolts that are to be roll threaded, for instance,

it is necessary that the portion to be threaded is smaller in the diameter than in the shank.

The stock used is the diameter of the shank and the

die is necked down at the desired place.

As the blank is pressed into the

die by the first punch, the advancing end is forced into the smaller diam­ eter.

This, of course, lengthens the blanlc a certain amount, and provi^

sion must be made for this in adjusting the stock stop. This is the know-how on the operating of cold heading machines.

Next,

the various detail operations involved in the production of hexagon and square bolts'will be described.

OPERATION ANALYSIS FOR COLD-HEADED BOLTS All bolts below the size of 3/U” x 8” are produced by cold-heading processes in the following operation sequence:

—52Operation 1

Heading Gutting the blank to the required size and heading: This operation is performed on a battery of machines, the working of which has already been explained# (See Headers and Working described before.) Operation 2 Trimming The formation of heads in cold headers is not exactly to the speci­ fications as the outeeming product of the cold headers usually consists of round heads.

These must in turn be trimmed to exact size and to square or

hexagon shape on special trimming presses at a second operation. Operation 3 Pointing Threading The clean blanks, with heads cut to size, are now fed into combina­ tion point and threading machines.

Pointing a bolt is literally just

that, but the operation is stopped before the end has been more than slightly beveled.

The purpose is to enable the nut more easily to engage

the first thread of the bolt.

Dropping from a hopper, the head of each

bolt is seized by a steel clamp, one of three spaced at 120 degree inter­ vals around a steel turret.

The turret runs through 1/3 of a revolution

and holds the blank while the spinning pointing tool advances against it. As the tool draws back, the chuck turns through 120 degrees and the thread­ ing tool advances under a stream of coolant to thread the bolt for just the right distance.

-53-

Operation

h Thread Rolling

As an alternative to operation 3, which consists of pointing and thread cutting, the purpose of of forming threads on the bolts can also be accomplished by another operation known as thread rolling. For bolts on which threads are to be rolled, the blanks from the trimming machine pass on to the thread rolling machine.

It should, how­

ever, be noted that in such a case the trimming operation should also in­ clude the extruding of the shank which is necessary before the threads are rolled. The formation of screw threads by cold rolling is effected by means of hardened rolls or dies having threads or ridges, which roll grooves into the blank and raise enough metal above the surface of the blank to form a thread. Most of the machines designed exclusively for rolling screw threads are equipped with flat dies.

One die is stationary and the other has a

reciprocating movement when the machine is in use.

The ridges on these

dies, which form the screw thread, incline at an angle equal to the helix angle of the thread.

The thread is formed in one passage of the work,

which is inserted at one end of the dies, either by hand or automatically, and rolls between the die faces, until it is ejected at the opposite end. Thread rolling machines are equipped with some form of mechanism that en­ sures starting the blank at the right time and also square ?d.th the dies. Thread rolling machines of flat die type are made both of horizontal and vertical design.

•a-

The operations in the manufacture of small bolts (up to 3 /I4." dia.) by using the modem cold working machinery are given on page 55 •

OPERATION ANALYSIS FOR HOT FORGED BOLTS All the bolts above the size 3/U" x 8" are produced on semi-auto­ matic hot headers.

The operation sequence is given below:

Operation 1 w Cutting This consists of cutting the bar to the required length, having taken into consideration the extra length of the bar required to form the head. Operation 2 Heating A portion of length of the bar is heated in a furnace before the bar is passed on to the heading machine. Operation 3 Heading Upsetting the bar and formation of head: The bar which is heated for a portion of its length, is placed in the impression in the stationary gripping die, and is gaged to length by a movable stop.

The machine is then operated and the movable die closes it

on the bar, gripping it rigidly.

The stop now rises, and, as the ram of

the machine advances, the plunger upsets the end of the bolt, and blocks provided for the purpose form a flat on each side of the upset end.

The

operator keeps his foot on the treadle, and as the movable die backs out, he rotates the rod one-sixth per turn.

This operation is repeated until

5 5*'

-56-

the head has been correctly formed.

Tie operator now removes his foot

from the treadle stopping the operation of the machine, when the dies re­ main in open position allowing him to remove the completed bolt. Dies for Hot Forming The following figure shows the types of bolt heading dies known as double deck three blow bolt dies, which are used for finishing hexagonhead bolts.

The two gripping dies A and B, as a rule, are made from

blocks of tire steel; each gripping die is made from three pieces to fa- ' cilitate machining.

The lower heading punch G is cupped out to form a

hexagon, and is held in the heading tool-holder, which is attached to the ram of the machine.

The upper punch D is held in the same way as the

lower heading punch, and forces the bolt into the hexagon impression in the dies after it has been roughly formed in the lower inpression.

This

type of die produces a bolt free from fins and burrs, and accurate as re­ gards size and shape.

The bolt is given one blow in the lower impression

and then raised to the upper die impression, where it is generally given two blows. (See figure on page 57 •) Operation U Removing the Flash This operation is necessary on bolts and rivets produced in contin­ uous 'bolt-making machines as it is practically inpossible to produce bolts without flash and other deformities in such cases.

However, where bolts

are produced on stop motion machines, this may not be found necessary. Following the forging operation, after the bolts have become cold.

-57-

POE HOT FORHXœ (BOLTS & RIVETS )

dies

MOVABLE

I

Stationary

MOVABLE

STATir'NARY

STATIONARY

[ S S îNG LE'BLO W R IVET DIES

rr _Lj

m ovable

I

'STATIONARY

—

OO U B LE-O EC K .TH R EE BLO'^ BOLT DIES

Fig. I. Plain Type of Bolt Forging Dies of Universal Applica­ tion. Fig. 2. Single-blow Rivet Dies. Fig. 3. Double-deck Three-blow Dies

C Moc^Ti-ACV'rf's

Ê-no,cle/»Ul«)

-58-

they are transferred to another machine where the flash is removed.

The

bolts are put in a chute attached to the flash removing machine and they pass down to a slide from which they are carried into the shearing dies by means of a segment carrier. %en the segment makes one-quarter turn, another slide operated by a bell crank and travelling in a position at right angles to the first carrier, picks up the bolt and carries, it to the dies.

The dies are in segment form and are operated from each side by

cranks that receive movement from a slide through the action of a cam groove. The trimming is accomplished by a punch in connection mth the dies, which forces the bolt right through the dies into a box under the machine, removing the flash that has been produced by the forging machines. Operation 5 Pointing or Chamfering As explained under cold forged bolts this operation corrects any forg­ ing defect and facilitates the starting of dies. The pointing machine may be a small bench machine operated by po?rer. One operator can turn out as much as 25,000 bolts of 5/8 inch size in ten hours. Operation 6 Threading Cutting threads on bolts is done on machines know as "Bolt Gutters". A typical design is shown on the accompanying illustration on page 59 . This is called a single bolt cutter because it has one spindle.

Some bolt

cutters have two, three, or four spindles and are known as double, triple.

-59-

1

I

et

î

I ! F

I

-

60-

or quadruple bolt cutters respectively.

For the project under considera­

tion, some multispindle bolt cutters will be used. The thread is cut by means of a die head A (see illustration) which is attached and revolved by the spindle of the machine.

The bolt to be

threaded is held in vise B which is operated and closed by a handwheel. C. The vise is mounted upon a carriage which travels along the bed of the machine.

Ihe carriage is traversed by the hand wheel at the rear of the oli«.

vise in order to start the bolt into the

and also for withdrawing

the bolt after the threading operation. While the thread is being cut, the carriage and the bolt are drawn forward by the action of the die, on the type of the machine illustrated.

The hand traversing movement of

the carriage is effected by a pinion which meshes vjith the rack. Threading Dies The threading die-head is so arranged that the dies are opened and closed automatically by the forward and return movements of the carriage, which is a feature common to bolt cutters of different designs.

The

clutch ring which controls the opening and closing of the die is operated by a swinging yoke D.

This yoke is actuated by the engagement of one of

the tappets E with the lever F, which may also be used for opening and closing the die by hand.

These tappets are mounted upon a rod connecting

with the carriage and they are adjusted in accordance with the length of the thread to be cut upon the bolt.

The construction of the die-head is

such that the dies, when closed, are securely locked in position. A spring operating in connection with the opening toggles serves to open the die-head rapidly.

The main spindle of the bolt cutter is hollow so

-6l-

that a long bolt may be extended back into the spindle.

The cutting

lubricant for the threading dies is supplied by a small pump. Multiple-spindle Bolt Cutters for Threading The bolt cutters having two or more spindles are used in preference to the single spindle t^Tpe where large quantities of bolts are to be threaded constantly.

These machines operate on the same general principle

as the single spindle design.

The spindles are parallel and each one has

an independent carriage and vise, so that while a thread is being cut on one bolt, another bolt is being inserted in or removed from vise of another carriage.

The carriages of the same bolt cutters, expecially of

the multiple-spindle type are operated by means of levers instead of hand­ wheels . Bolt cutters are equipped with lead-screw so that the carriage.will have a positive feeding movement when a thread is being cut, in order to prevent inaccuracy in pitch of the thread. IThen a bolt cutter does not have a lead, screw, the feeding movement of the carriage is derived from the action of the dies upon the thread being cut.

This method of feed­

ing is satisfactory when cutting such threads as the U. S. Standard, or a ^%itworth thread. Tdien cutting square threads, however, or those of the special form or when threading long work where cumulative error becomes important, a lead-screw is necessary. The use of a lead screw prevents the die from cutting a thread which gains or loses in pitch, because the movement of the carriage is positively controlled.

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SECTION TEN

FINANCIAL ESTIMATE

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Section Ten PIMNGIÂL ESTIMATE In this section an attenipt is made to give an approximate estimate on the financial aspects of the enterprise under consideration. Based on all the plans made so far in the previous sections, the following items are calculated: (A) Total investment to be made^ (B)

The manufacturing and selling cost of the product^ ««»