How |O Cut Screw Threads Ln the Lathe

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BULLETIN NO. 36A

How |o Cut Screw Threads ln® the Lathe

Cutti^g a Screw Thr.ad.

Price lO Cents Postpaid toAnyAddress Coin or StlmPS Of Any Country Accept.d

SOUTL! BEND LATHEWORKS 456 NILESAVE. SOUTH BEND, INDIANA, u.S.A. MIMS Machinery Movers mimsriggers.com

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Screw Threads

The history ()i the origin ancl (le\.elopment of the screw thread is lost in antiquity. IIo\\-e\.er)it iskno\\-I that scre\\. threads \|.ere used more than 2000 \,ears ago alrd that screws and bolts \\.ere used for i:lsten- ing together \.arious parts of the armor \\-om by ancient Roman \\-arriors. Thl-ended cle\.ices \`,ere also used to open and close heat.), doors and dra\\.bridges of ancient castles. The de\.elol)ment of modern mechanical (Ie\,ices has been made possible by the im.ention and (le\elopment of the scre\\, thread. The most important use of threads is for fastening parts of machinery and equipment together. \1'ith screws and bolts parts can easily be assembled and taken apart \\,ithout damage) but \`.hen fastened by other methods, such as welding. ri\.ets. nails. etc.. this is not possible. screws are also used for transmitting motion) such as the lead screw, cross feed screw) etc. of a lathe, also for let,erase as in jack scre\`.a. \,ises and clamps. The screw is also used in I)recision measur- ing instruments. such as micrometer caliI,erS. Cross feed of lathe) etc.

South Bend Lathe Works

col)yrighI, |938. by South Bond Lalho Works. All rights reBOrVOd. MIMS Machinery Movers mimsriggers.com

Fig. 1' Cutting a Screw Thread in the Lathe.

How to Cut Screw Threads ln the LatLle

Cutting screw threads in the lathe is accomplished by connecting the headstock spindle of the lathe with the lead screw by a series of gears so that a positive carriage feed is obtained and the lead scre\y is dri\.en at the required speed with relation to the headstock spindle.

The Searing between the headstock spindle and lead screw may be arranged so that any desired pitch of the thread may be cut. For example) if the lead screw has eight threads per inch and the gears are arranged so that the headstock spindle revolves four times \\.hile the lead screw revolves once) the thread cut will be four times as fine as the thread on the lead screw or 32 threads per inch.

The cutting tool is ground to the shape required for the form of the thread to be cut, that is "y," Acme, square, etc. The de])th of the thread is determined by ad-

justing the cross slide.

Either right hand or left hand threads may be cut by reversing the direction Of rotation of the lead screw. This may be accomplished either byadding or removing one idler gear in the change gear train, or by shifting the tumbler gears on the headstock. i MIMS Machinery Movers mimsriggers.com

FOR}I|'I.A I

\-u Th'd>, Per ln. I)-I)epth-I x-61952 F=FhI--P 8 Fig. 2. American National Screw Thread Fol.m (Formerly U. S. Standard Screw Thread).

American National Screw Threads

The National Screw Thread Commission in l928 \\.as authorized by Congress to establish a Standard system Of SCre\1. threads for use in the I_nited States. As a result this commission estal)lished the.American i_ational Screw Thread System \\.hich has been approved by the secretar_\. of \\-ar) secretary of the r\-avy) and-congress) and is now generally used by all shops in the United States.

The form of the thread adopted is shorn abc)\.e and tables for both the Fine Thread Series and Coarse Thread Series are given on the opposite page. The tabu- lation at the bottom of page 3 lists a number of special pitches of scre\\- threads that are commonly used. However, the standard screw threads should all+.ays be used) if possible.

A report of the National Screw Thread Commission applying to screw threadsl bolts, machine screws, etc. defines the follorving terms.

Terms Relating to Screw Threads

screwThread. A ridge of uniform section in the form of a helix on the surface of a cylinder or cone.

ExternalandlnternalThreads. An external thread is a thread on the outside of a member. Example: A threaded plug. An internal thread is a thread on the inside of a member. Example: A threaded hole.

MajorDiameter (formerly known as "outside diameter')). The largest diameter of the thread of the screw or nut. The term "major diameter" replaces the term <(outside diameter" as applied to the thread of a screw and also the term "full diameter" as applied to the thread of a nut.

Minor Diameter (formerlv known as "core diameter''). The smallest diameter of the thread of the screw or nut. The term "minor diameter" replaces the term "core diameter" as applied to the thread of a screw and also the term "inside diameter" as applied to the thread of a nut.

Pitch Diameter. On a strait`oht screw thread. the diameter of an imaginary cylinder) tlle surface of \l.hich \+-ould pass through the threads at such points as to make equal the width of the threadsandthe\1-idth Of the SPaCeS Cut bV the Surface Of the CVlinder.

Pitch. The distance from a point on a screw thread t() a corresponding point on the next thread measured parallel to the axis.

Lead. The distance a screw thread advances axially in one turn. On a single- thread screw, the lead and pitch are identical: on a double-thread screw the lead is twice the pitch; on a. triple-thread screw) the lead is three times the pitch, eta. 2 MIMS Machinery Movers mimsriggers.com American National Standard Screw Threads and Recommended Tap Drill Sizes

Coarse Thread Series (N.C.) Fine Thread Series (N.F.) Formerly U. S. Standard Formerly S. A. E. Th'e.d

American National Special Screw Threads (N. S.) and Recommended Tap Drill Sizes MIMS Machinery Movers mimsriggers.com

Fig' 3. Change Gear Equipment Used on Standard Change Gear Lathes.

Setting Up Standard Change Gear Lathes* for Cutting Screw Threads

Screw threads are cut on Standard Change Gear Lathes ty engagillg the apron hllf rlutS \\.ith the lead screw. The pitch of threacl to be cut is de- terminecl lIV the number Of teeth in the Change gears uSeCI Om the re\-erse StuCl and the lead screw, also the compound gears \\.hen used- To set up the lathe for cutting a screw threa(1, first dc.tcrmine the numbl.r of threads per inch to he cut. By referring to the cha.ngre gear chart attachecl to the lathe (Figr. 4) the chant,cre goal-S required Can be determine(1. The threa(I to I)e cut should be located in the first cc)lumn under ttle lleading "Threads per Inch.,, Ill the SCCOlrd COlumn under the Ileadillg "Stu(I Gear" is listed the number of teeth in the chang-e gear \\.hich should be placed on the rc,verse stud (A) of the lathe. (See Fig. 3.) In tile third COlu-1 under the headlng "Idler Gear" is listed the fig.ure number of the cliagrlm on the index chat-t showint,a. the correct arrangement of i(ller gear an(I cl""p(""d gears. Ill tlle fourth column uncler the hea(ling "Scrc\\r Gear" is listed the llumbCr Of teeth ill the gear tObe I)laced On the lead Sere". (C).

After sclccting. the aha"ge a,crears necessary for cuttimg the desi1-ed thread. place them on the reverse stu(I ancl lea(I screw respccti\-cl}. and co-ect thenl \\,ith the idler gear an(1 conlPOund gears, aS She"m On the Change t.a-ear Chart I Procedure for 9-inch I.Workshol," I-athe i9 Same aS for Standard Change Gear Lathe.

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Fig. 4. Change Gear Chart for |0" Standard Change Gear Lathes. SiTnilar Ct`arts at.a used On Other Sizes Of Standnrd Change Gear Lathes'

The spacing colla1. On the lea(I scre\\. nlust bc place(I olltSi(1c the scre\\.

gear) as sho\yn in 1.`ig.- 5. \\.hen simple gc.arillg. iS uS(.(1. ancl inside tllc sc1.e\r gc.ar, as sh(""I ill Fig- 6. \\.hc.n c.("lil")uml grt.:lt.ing is tlSe(1.

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F'ig. 5. PositioT' Of Spacing Collar Fig. 6- Position of Spacing Collar far Simple Gent.ing. for Compound Gearing. MIMS Machinery Movers mimsriggers.com Adjusting Levers of Quick Change Gear Box for Cutting Various Pitches of Screw Threads

The only difference bet\+.eon the Quick |'hange Gear Lathe ancl the Standard change Ge'ar Lathe is that the Quick l,ha-nge Gear Lathe is tired \\.ith a gear box which permits obtaining \,arious pitches of screw threads l\ithout the u=-e ()i loose change gears. (See Fig. 7.)

The scre\\. thread chart is attached to the gear bo-i. aS Shout-n in 1.'ig. 8 below. This chart reads directly in threa(lS Per inch. 1l is onl_\. necessal.y to arrani!i the levers of the gear box as in(licate(I all the ill(let pl:lie ill OrCler to obtain \-alious _ccrew threads and fee(ls

The I)itch Of the threilCl tO IJe Cut is determine(1 by smtini! the sli(ling gear A. top let.er B :m(I tumbler le\.er C of the quick change i!car box so that they confl)rm \\.ilk the threa(I clltting chart. For examl)let to cut 3 threa(ls per inch the sli(ling gear A is pushe(I in. the top le\-er B on the gear box is 1)llShed tO the extreme left p()sitioIl an(I the tumbler lever C is I,lace(1 ju-.I below the column in MIMS Machinery Movers mimsriggers.com Lathe Tools Used for Cutting Screw Threads

The point of the cutter bit must be ground to an angle of 6Oo for cutting screw threads in the lathe. as shown in Fig. 9 at right. A center gage or angle gage is Fig.9. Center gnge used for checl{ing angle of cutter bit ground lot. cutting screw threads. used for grinding the tool to the exact angle required. The top of the tool is usually ground flat, with no side rake or back rake. However, for cutting threads in steel, side rake is sometimes used. A formed threading tool is usually used if considerable threading

is to be done. Figs. ll and l2 il- Fig. |0-A. End View Fig. 1O. Side View of lathe of lathe tool cutter lustrate two good types of formed tool cutter bit ground for cut- I.it ground for cut. threading tools. The formed tir'g screw threads. ting screw threads. threading tools require grinding on top edge only to sharpen and therefore always remain true to form and correct angle. For cutting American \_ational Standard Screw Threads finer than 10 per inch) the point of the tool is usually left sharp or u.ith a very small flat to pro- \'ide clearance at the bottom of the thread. Hc)wever' F'ig. ll. Formed threading tool, for cutting coarser I)itches of threads and when maxi- solid type. mum strength is desired) the point of the tool ma), be ground flat) as shown in Fig. 13. The flat on the point of the tool should be one-eighth of the pitch. (See Fig. 2, Page 2.) The illustration at the bottom of the page, Fig. l4) shows a gage \+-hich mav be used for grind-

ing threading tools to Fig. l2 Fol.mad threading tool, the exact angle re- spring type. quired fc)I standard screw threads. r\-ote that the gage sho\`.s T`.-.._'-` the flat for the point of the tool as well as

the exact an.gle and FIB. |4. Standard screw thread tool gage for grindlng EEEEE depth of thread. threading tools. Fig. l3- Forged steel threading tool.

T|'].en cllt[illU.SCrelU ll".C(I(lS in SIC(>l llSC I)lenlU 0/ ()i[ an(i a snlO(Jl1\ lhrc(Ill ll)ill I.e.Sl|ll. MIMS Machinery Movers mimsriggers.com Correct Position of Lathe Tool for Cutting Screw Threads

For External Threads

The top of the threading tool should be placed exactly on center. as sho\`.n im Fig. 15 at right) for cutting extemal screw threads. Note that the top of the tool is ground Fig. l5. Top of cutter bit should be set oI` Center for flat and is in exact alignment with cutting screw threads. the lathe center. This is necessary |o obtain the correct angleofthethread.

The threading tool must be set square with the work) as shown in Fig. l6. The center gage is used tO adjust the point of the threading tool and if the tool is carefully set a perfect thread will result. Of course) if the threading tool is not set perfectly square with the work, the Fig. 16. Cutter blt should be set square with worl{, as angle of the thread will be incorrect. shown above, for cutting exterllal screw threads.

For lntemal Threads

The point of the threading tool is also placed exactly on center as Fig. l7-Forcutting in- shown in Fig. l7 at right for cutting ternal screw threads| top oF cutter bit should internal screw threads. The point of be setexactly on center. the tool must be set perfectly square with the work. This may be accomplished by fitting the point of the tool into the center gage) as shown in Fig. l8 at right.

When adjusting the threading tool for cutting intemal threads. allow sufficient clearance bet\+-een the tot)I and the inside diameter of the hole to I)ermit backing out the tool when the end of the cut has been reached. However the boring bar should be as large in diameter and as short Fig, 18- Cutter bit should be set square with work. as as possible to prevent springing. shown above for cutting into-Elf Screw threads. 8 MIMS Machinery Movers mimsriggers.com

Fig. l9. Compound rest of lathe set at 29O anglc` for a"tting screw thl.Cads.

PositI.On Of Compound Rest for Cutting Screw Threads

In manufacturing plzmts \\hcre maximum pro(luclioll is desired it is customary to place the c"mpound rest of the lathe at an angle of 29o for cutting screw threads. The compound rest is s\1.uns around lO the right) aS shown in Figs. l9 and 20. \\_hen the c()mpound rest is set in this I)osition and the compound rest screw is used for adjusting the depth of cut. most of the metal is re- moved by the left side of the threading tool. (See Fig. 2l.) This permits the chip to curl out of the \\.ay better than if tool is fed straight in) and preyents tearing the thread. Since the angle on the side of the threading tool is Boo, the right side of the tool \+.ill sha\.e the thro:Ill smooth and produce a nice finish) although it does not Fig. 20. Correct angle of compound rest for thread cutting. remove enough metal to interfere \\ith the main chip which is taken by the left side of the tool.

Fig. 2l. Action of thread cutting tool when com. pound rest is sot at 29O angle. MIMS Machinery Movers mimsriggers.com I_ II

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Fig. 23. Latt'e dog should be tight when work is mounted between the lathe centel.s for cutting screw threads.

Mounting the Work in the Lathe

\|'hen mounting `\.orb between the lathe cen- ters for cutting screw threads.makesurethelathe dog is securely attached before starlin.g to cut the thread. If the do(,cr should slip the thread \`,ill be ruined. \_ever remo\.e the lathe dog from the work until the thread has been completed, and if it is necessary to remo\.e the `\.ork from tile lathe before the thread is fmished makesurethat the lathe dog is replaced in the same slot in the face plate. Fig. z4. Chuck jaws should be tight whel` cutllng screw threads. \\'hen threading \`,orb in the lathe chuckmake sure the chuck ja\\.s are tight and the work is \+.ell supported. The chuck must be tight enough on the spindle to pre\.cnt unscre\\.ing when the lathe is reyersed. \-e\.er remo\.e the \\-()rk from the chuck until the thread i< fmished. \1'hen threading long slender shafts. use a fol- lo\+-er rest, as show,n in I..ig. 26. The center rest may be used for su]lporting hng \1.Ork Such aS

pipe \`-hich is to be tllreade(I nn the inside.

(See Fi..c,. 27.) Fig. 25. \Vork should be pushed bacI{ in chuck and well supported.

Fig. 26. Cutting a long slender screw thread' with the aid of a follower rest.

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Fig. 28. Thread cuttil`g stop attached to dovetail of saddle.

Adjusting the Thread Cutting Stop

On account of the lost motion caused by the play necessary for smooth operation of the change gears) leadscre\+,) half nuts, etc., the thread cutting tool must be With- drawn quickly at the end of each cut) before the lathe spindle is reversed to return the tool to the starting point. If this is not done, the point of the tool will dig into the thread and may be broken off. The thread cutting stop may be used for regulating the depth of each successi\.e chip.

The point of the tool should first be set so that it just touches the w.Ork) then lock the thread cutting stop and turn the thread cutting stop screw until the shoulder is tight against the stop. when ready lo take the first chip run the tool rest back by turning the cross feed screw to the left se\.eral times and move the tool to the point where the thread is to start. Then turn the cross feed screw to the right until the thread cutting stop screw strikes the thread cutting stol). The tool rest is now in the original position) and b), turnint.c, the compound rest feed screw in.002" or.003,, the tool will be in a position to take the first cut.

Micrometer Collar May Be Used in Place of Stop

The micrometer collar on the cross feed screw of the lathe may be used in place of the thread cutting stop) if desired. To do this, first bring the point of threading

tool up so that it just touches the \+,orb, then adjust the Fig. 29. Micrometer collar on cross feed screw of lathe. micrometer collar on the cross feed screw- to zero.

All adjusting for obtaining the desirecl cleplh of cut should be done \\.ith the com- I)Ound rest Screw. |\-ithdra\Y the tool at the end Of each Cut by turning the Cross feed screw to the left one complete turn. return the tool to the starting point and tum the cross feed screw to the right one turn. stop])int,c' at zero. The compound rest feed screw may then be adjusted for any desired depth of chip. ll MIMS Machinery Movers mimsriggers.com Taking the First Cut on a Screw Thread

Take Ligllt Trial Cut to Check Lathe Set-up

After settillc30.uP the lathe. aS eXPlaimed on the preceding pat,rres. arrange the lathe for a slow, back-Seal-i.d SPin(lie SPeed an(1 take a vcr)I light trial cut jtlSt CICCI) enOugll to

scribe a_ line on the s|ll.fz|ce of the \yo1.k-. aS Fig. 30. Trial cut to check set.up for showll in Fig. 30. The purl)ose of this trial thread cutting. cut is to make.sllre that tlle lathe is art-zlllg- ed for cutting the desired pitcll Of thread.

To check the number of threads per inch) place a scale against the \t-orb) as sho\\.n in Fig. 31 so that the end of the scale rests on the point of the thread or on one of the scribed lines. Count the spaces between the end of the scale and the first inch mark, and this \\-ill giye you the number of threads I)er inch.

It is quite difficult to accuratelv count fine pitches of screw threads. as described above. A screw thread gage as illustrated in Fig. 32 isvery convenient for checking the finer pitches of screw threads. This gage consists of a number of sheet metal plates in which are cut the exact form of the various pitches of threads and each plate is stamped with a number indicating the number of threads per inch for which it is to be used.

The flnal check for both the diameter and pitch of the thread may be made with the nut that is to be used or with a ring thread gage, if Fig. 32. Screw thread pitcl` gage. one is ayailable. Fig. 33sho\\.s how the nut may be used for checking the thread. The nut should fit snugly \\-ithout I)lay or shake but should not bind on the thread at any point.

If the an.gle of the thread is c()rrect and the thread is cut to the correct depth it \`.ill flt the nut perfectly. Hot+,e\.er, if the angle of the thread is incorrect or the lead is incorrect, the thread may appear to fit the nut but will only be touching at a fe\\. points. For this reason the thread should be checked by other Fig. 33, Screw thread properly fitted methods in addition to the nut or ring gage. \o nu|.

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Fig. 34. Applying lard oil to work with small pait|t brtISh while cuttit'g screw threads in a tool steel thread gage.

Use Lard Oil When Cutting Screw Threads in Steel

Lard oil should be used w.hen cutting screw threads in steel in order to produce a smooth thread. If the oil is not used a very rough finish will be caused by tearing ol- the steel by the cutting tool.

If lard oil is not a\.ailable any good cutting oil or machine oil may be used. If trouble is experienced in producing a smooth thread, a little I)O\\.dered Sulphur may be added to the oil.

The oil should be ilpplied generously preceding eacll Cut. A small paint brush is ideal for applying the oil \+.hen cutting external screw threads, as illustrated abo\.e. Since lard oil is quite expensive. many mechanics place a small tray or cup just below the cutting tool on the cross slide of the lathe to catch the surplus oil which drips off the work. In manufacturing plants where the lathe is to be used exclusi\.el_v. for cutting screw threads in steel it is customary to equip the lathe with an oil pan and oil pump to provide a continuous flow of oil.

13 MIMS Machinery Movers mimsriggers.com Resetting the Tool After the Thread Has Been Started

If the thread cutting tool should need re-Sharp- ening) or if for any other reason it is necessary to remove the thread cutting tool before the thread has been completed, the tool must be carefully re- adjusted so that it will follow the original groo\,e when it is replaced in the lathe. There are set.Oral methods by which this can be accomplished. _ Before adjusting the tool) Set the POint Of the Fig.35. Adjusting I,oint of threading cutter bit square with the \\.ork) as described on tool to conform with thread. page 8, and take up all the lost motion in the change gears, half nuts) etc.. by pulling the belt for\`-ard by hand.

If the lathe has a compound rest) the COmPOund rest top may be Set at an angle, and by adjusting the cross feed scre\\. and compound rest feed screw simultaneously the point of the tool can be made to enter exactly into the original groove.

If it is not convenient to use the compound rest for readjusting the threading tool) the lathe dog may be loosened, the work tumed so that the threading tool will match the groove and the lathe dog tightened.

Another method that is sometimes used is to disconnect the rev.erse gears Or the change gears. turn the headstock spindle until the point of the threading tool enters the groov.e in the work, and then reconnect the gears.

Finishing the End of a Threaded Piece

The end of the thread may be finished by any one ot set.eral methods. The 4So chamfer on the end of the threa(I, as shot+.n in Fig. 36) is commonly use(I for bolts. cap screws, etc. For machined parts and special screws the elld iS often finished bv roun(ling with a form- ing I"ol, as shot-1,n in Fig. 37.

It is difficult to stop the threading tool abruptly so some p--ision is llsu- ally made for clearance at the en(I of the cut. In Fig. 36 a hole has been drilled in the end of the shaft, aml in Fig. 37 a neck or hrrroo`.e has been cut around the shaft. The groo\-a is I)refer- able as the lathe must be run \-Cry slowlv in order lo obtain satisfactory results \\.ith the drilled hole. MIMS Machinery Movers mimsriggers.com

Fig.38. Thread dial indicator attached to lathe carriage.

Use of Thread Dial Indicator in CuttI,ng Screw Threads

A thread dial indicator or thro:ldin,,rr clock is usually used for cuttinf.a lonf,or screw threads. This de\-ice permits disengac,c,in[,cr the half-nuts at the end of the cut, returning the carriage to the starting point bv hand, and then en- gaginc,c, the half nuts at the correct time so that the tool will follow the ori.qinal cut. This sat.es time on long tIlreadS :lnd iS: it alsc) eliminates the necessity of re\.ersinq thelathespindle.

The threading dial consists of a \+.orm \+-heel which is attached to the lo\\er end of (i shaft and meshed with the Fig'39 Face of tllread dial ind|cator. lead scre\+.. On the uI)Per end Of the Shaft iS the dial. --\S the lead screw reyol\.es, the dial is tumecl ancl the numbers on the dial indicate points at \\.hich the hall- nuts ma}, be engaged.

\\'hen cuttin..a, short threacls it is better lo lea\-a the half-nuts engaged with the lead scre\\.. and \\.hen the en(I of the cut is reached. withdraw the tool and reverse the lathe spindle to retum the tool to the starting point.

Rules for Operating Thread Dial on South Bend Lathe

For all e\.en numbered threads, close the half nuts at any line on the dial.

For all odd numbered threads. close the half nuts at any numbered line on dial.

For all threads in\-olying one-half of a thread in each inch, such as llJ/2) Close the half nuts at any odd numbered line.

The thread dial cannot be used \yhcn cutting metric screw threads.

15 MIMS Machinery Movers mimsriggers.com Cutting Multiple Screw Threads

Multiple screw threads are used for adjusting screv..s and other applications where a coarse lead is desired. The depth of the thread is less than for a single thread of equal lead. making a stronger screw.

-i multiple thread hating two grooves is who\yn as a double thread) one hat.ing three grooves a triple thread. etc. (See Fig. 4O.) The pitch and lea(I of a multiple thread Fig. 4O. A multiple screw thread having should not be confused. The pitch is the dis- two grooyes (Double Thread) lance from a point on one thread to the cor- resl)onding point on the next tbreild, `\.nile the lead i5 the distance a SC-. thread ad\.ances ln one turn.

\\.hen cuttin|, multil)le threads in the lathe the first thread is cut to the desired depth. The w.orb is then re\-ol\.ed part of a turn, and the Second thread Cut, etC. In order to obtain an exact spacing it is advisable tO mill aS many equally SPaCed slots in the face plate for the lathe dog as there are multiple threads to be cut. I.`or a double thread. t\\.o slots; a triple thread, three slots. eta. If it is not convenient to cut slots in the face plate. equally sl)aced studs may be attached to the face plate and a straight tail lathe dog used.

Another method for indexing the work when cutting multiple threads is to dis- engage the change gears after the first thread has been completed and turn the spindle to the required position for starting the next cut. If a double thread is being cut and there are 48 teeth in the stud gear, the spindle Should be turned until 24 teeth hat,e been passed, then the gears engaged and the See()nd thread Cut.

Cutting Left Hand Screw Threads

A left hand screw is one that tums counter- clockwise when advancing (looking at head of screw) as shown in Fig. 42. This is just the opposite of a right hand screw. IJeft hand threads are

used for the cross feed screws of lathes, the left Fig. 4|. A left hand screw thread. hand end of axles for a|ltomobiles and \\.ar.c'ons. one end of a turnbuckle. some pipe threads, etc.

In cuttingleft handscrewthreads the lathe is set up exactly the same as for cutting right hand scre", threads) except that the lathe must be arranged to feed the tool from left to right.insteadoffromright Fig 42. A left hand screw advar'ceS to left) when the spindle is rev.ol\.ing for"-ard. when turned counter_clockwise.

16 MIMS Machinery Movers mimsriggers.com How to Calculate Change Gears for Cutting Screw Threads

If it is necessary to cut a special thread that does not appear on the index chart ()i a lathe or if no index chart is a\.ailable, the gears required can easily be calculate(I. All South Bend IJatheS are eV.en Seared; that iS, the Stud gear revolt.eS the Same number of revolutions as the headstock sl)indle, and when gears of the same size are used on both the lead screw and stud) the lead screw and spindle rev.ol\.a the same number of revolutions) so it is not necessary to consider the hr'earing between thl. headstock spindle and the stud gear when calculating change gears.

If simple gearing is to be used, as shot+.n in I.'ig. 43) the ratio of the number of teeth in the chant,c'e gears used `\.ill be the same as the ratio between the thread I() be cut and the thread on the lead screw. For example. if lO threads per inch are to I)a cuton a lathe hat.ing a lead screw with 6 threads I)er inch, the ratio of the change gears would be 6 to lO. These numbers may be multir)lied by any common multiplier to obtain the number of teeth in the change hoe:+rs that sh()uld be used.

Rule-To calculate change gears. multiply the number of threads per inch to be cut alld the number of threads per inch in the lead screw. I)v the same mumber.

Example: Problem-To cut lO threads per illCh Oil lathe hat.inhc' lefld sol.eW with 6 threads per inch. Solution- 6 x 8 = 48 - \-o. of teeth in gear on stud. 10 x 8 - 80 -\_a. of teeth in gear on lead screw.

If these gears are not to be found in the change gear set, a.ny other number may be used as a common multiplier, such as 3) 5, 7) eta. When compouncl Searing) as shown in Fig. 44, is used, the ratio of the compound i(1Ier t.a-ears must also be taken illtO COnSi(leratiOl1, 1)ut other\\.ise the ca1- culations are the same as for simple gearing. For e.T{am1)1e, if tllc coml)otmd idler gear ratio is 2 to 1. the threads cut are just twice the number per inch as when simple gearillg i-lSed.

Diagram Showing Simple and Compound Gearing

Fig. 43. Simple Searing. l7 MIMS Machinery Movers mimsriggers.com Using Taps and Dies to Cut Screw Threads in the Lathe

TaI)S an(1 dies are often used for cutting sc-. threads ;n the lathe, especially in faclorics \\-here maximum procluction is imI-tant There are se\-Oral ".a.\.a in which the lathe mav be set up for this kin(I of ",ork' as illuStrateCl btlO\`,.

Fig. 45shows a common hand tap being used to thread a llut \`hiCh iS held in the lathe chuck. The handle of the tap \"ellch rests against the \- \`Zl), Of the hthe I)eel. and as the hthe spindle re\,ol\.es slo\\.ly the tail-stock hand "heel is turnecl to feed the tap through the nut plellty of oil shoul(I be uced (m the tap if the nut is n-le of steel.

Fig. 46 shows a self-opening die mounted in the taill=ock spin(nc ("- the lathe for cutting threads on studs. -+(ter starting the lathe spindle the tail+tuck is pusbe(I b), ham(I along the lathe be(I until thedie takes hold aml Starts tO Cut the thread, after u,hich the clie "ill I)ull the tailstock along. ,i die holder can be made for the tailstock to hold comm(m button dies, but if the.y are used it is net,eSSar), tO re\er`e the lathe spindle \\.hen tile end of the thread h:ls been reached.

Fig. 47 shows a die nlOunted On the tool rest Of the lilthe. \\_hen mOullted in this manner the lead scre\\. and half nuts of tlle lathe may, I)e use(I to feecl the die so a pert-eat lei"1 i> obtainecl in the thread cut. Fig. 48sho\\-s a lathe equippecl with special fl-`lure fur hal(ling the \`-ork on the face plate. ancl a turret for hal(ling drills. boring bar and taps for boring and threading thehole.

Fig. 45. Using a tap for threading a nut I;g. 46. I)ie mounted in tailstock of lathe iou in the lathe. threading studs.

Fig- 47. Die mounted on lathe carriage for Fig' 48. Tap mounted in lathe turret for cutting accurate threads. threading special l`uts. l8 MIMS Machinery Movers mimsriggers.com Standard Screw Thread Forms

A|lEIllC:I+ X_lTIOX.|I. SCREW TIIREAD /I.'ormerl}- U. S. Stan(llrd Scrc\\. Thr|.art)

I._OR}lt I, \ 1) = Plllh i_ I ----- i-a lh'(l> I,rrI D-lJ(.I)th-I x 6i95? I) F==l.1'lt=- 8

FREItCII _lND IXT1._,RX,1TIOX_1L SYSTEM STJX1)ARD SCREW THEE:1D I,'olt _\1 UI,A I-P|tchiI1 }I_\I I) -=I)cpth of Ellg:`pe- lllellt-I x.o19.5 ]t=-Dcptl| of 'l`hrc:|d ---=P I .(l915 I -_\ILIXllIIum lt:|dius -P x .Ol;.'33 P I' r1,\t-a.

W'IIITT+'ORTII STANDARI) SCREW TIIREAD

\J5/ FOR|I|-I,A I I-PIlch=- \-(> T1|'ds. Per ln. D-I)t.I)th-P. x 610.?

R_-_Ra(JIu-- 1`i7 U

i SQUARE SCRI-.W THREAD FOR}[|-L\

i I-Pllch= _\\) 'Ihd> l'(.rln

D==D(.pt1\= I'.\_GOO

F==SIt.let.=-P x 50O

ACME SCRII.ll' THR1=JI) p| ")R""\l

i_u lhl1\ Il(,rln I)-I)el)t1|-,_ P + C10 F=I-lat=.;ro7 I (I--Ill,lI-=_i707 T`-rx)S_,

a SH^RPE. Zoo W'OR|I SCRE|+I TIIREAD

1.'OR}lL'L \

pJ I.-"\"` - \_I, 1l I (lh I|t.rln.

I)-IJtptI - (1866P

I.'- ll I _31 P C=rl,ll= _135P. MIMS Machinery Movers mimsriggers.com Transposing Gears for Metric Screw Threads

In Fl-:"lc-c. a"(I othc.1- P"-tS ( I I.:m.o1)e thl. lnt(.1.natI()1|al Stu|(ku-(I .\I|.tl-ic S|.1.i.\\- Threa(ls ln(I otllt.1- +\\lC.nth OI m(.trlC tlU-i.,,I(I+ Zll.e uS|.(I. I hcse tllH.Z-I(h art. u\(.(I i.\tt.mi\.C.l\- On mi|-ro- ll.(J])C.i. I(.Ic`l.opt.+ "I(I oth(.I o1)tic:I-I ,"ld SCictl- til'll. lml1-umC.nt-i :"I(1 stir.g-I(.:ll 1-t1.111mlltS.

\h.t1-iC thrC.ZL(ls al.e mC.:lt'm.Cd ill tll|. 1\Iet1.iC S\.item imt("(I ot- "l the E"gli.h s\>lcm. a""I m ( "k.I. toc\lt thclll (m :I I:lthl. llZ"ing-"l Eng- 1i`1l k.ad -.c.I"\-, m(.tliC tl.Zm`I"l`ing f,a-(,a1-I lllu-`l I)c tls(.(I- lhl. r

tl|r(.:I(ls. Fit,I 49. Metric TI-aml,OSinP Gears Attached to I_othe. "\[c.tlic. tr.,m+poì"g- i:l.:"-I arc. sul)1)lie(1 for I")tb Sl"l(kl"I |'l-lge (;l.ill- L.,LtIIC` Zlml OlliCk chz"lgc. Gc.al- I,:lthc` 1""ingr I..Jlgli.Ìl_k.[1d "`crl.".,+. ,\ melzLI ch,.".t ,ÌmiI:"- to F-ig. 51, sllO\\-- illgr tllc. '"i."li:i.-mt ot' lhc. gre<."-.s l'ol- cuttlngr \-".")u+ 1)itClll.` Of mCt1.iC .`C1.C\\. th1-ea(1s, is :LttaChe(1 to (.ach lzlt1|e.

Thc. i-orm ol' thc. mc.tric tl|r(.a(I is sim'1Ial. to the -\1m.riC:ln \`atiOl1<,ll Scre\\- Threzld fo1.nl, I"",ills- a r)Oo i"cltl(li"a a"grlc all(1 a fl:lt at thc. tol) ot' tlle tl"-c,I(I. I"lt :I -I-,Ill rzl(li\ls at tile ro()t ()I- tl1(. tl"-Cad 1"-O\.i(lCS gTeatel. Clearance. (See Figr. 50.)

FORMUI.A P=Pitch in MM i D-I)cT,th Of Enpage- m|,nt=P ;{ .¢JO.5 I ll H-Dl.!lth of Thread -I' I .694.-) r-Maximum Radius =P x .0633 r F_Flat=£ Fig. 5|. Metric Thread Cutting ` charc for I.alhe with English Thl.Cad Lead Screw and Metric Fig. 50. International Standard Metric Screw Transposing Gears. Thread Form.

International Stenderd Metric Screw Thread

Fig. 52. Metric Transposing Gear Attachment for 16', Lathe. MIMS Machinery Movers mimsriggers.com

Fig. 53. A Standilrd Change Gear Lathe with Metric Lead Screw.

Lathe with Metric Lead Screw

}Ietric lathes equipl)ecl \\.ith metric lead scrc`\s arc u`C.Cl \\.here -.tl-iC scre\\, threads are cut exclusively. Tlle metr:a lathe :s i(ll."tlCal \\ith the Ellglish lathe) excel)t that the lead scre\`', cross feed screw and colllPOund rl.St SCre\\, hate metric threads an(I all t,a-racl\lated collars read in the llletriC S}.Stem instead of the Ellglish system.

challge gear equilmlent SuPPliC.d \\,ith tlle hthe I)ermits cuttillg either 1.it,a-ht hand or left hand metric scrc\\, thrl.acts. -,\n index chart (Fig. 54) is zltta-ched to the lathe to show the a-"1gCment Of the chant3O-e gea1.S for Cuttillg the Various

pitches of tllreads.

when it is necessar\, to cut both English and metric screw threads, an FJlgrlish lead screw \\.ith metric trans1)OSing equiprlent Fig. S4. Index Chart far Standard Change is prefc1-able tO a metric leaCt screw. Gear Lathe with Metric Lead Screw.

21 MIMS Machinery Movers mimsriggers.com

At L.ft-No. 444-Y 9. _T{ 3' Model A South Bend "Workshop" Adjustable Horizontal Motor Driven' Back-Geared Screw Cutting Precisiol\ Bench Lathe.

One of the finest small lathes wc have I.vcr built.

At Right-No. t87-YN IO" xNe3i-Lilon:helCs1:cuttChaEiaecfay

Underneath Belt Motor Drlven. Quick Change Gear. Back-Gtared Screw Cutting Preci8|On Bench Lathe. A pc'pular type high qual- ity precislon lathe.

At left--No. 8ll7-C l6rvx 6' New Mnd>l South Bend Tool P\oom Unclerneath Belt Motor Driven. Quick Change Gear. riack-Glared Screw Cutting Precision Lathe.

A praLCtiCOl, t;ffieient and ular |y\otor clriven lathe.

Below---The plant of the south Bend hat_he Works at nc±6 3:guatnh,.::,n.dn. :na:i:.nua;a.dThiin9 'jXut: l906 and has grown and de- veloped to adnnan:::hpli9Cg=i;:l£yair:;ga tohfC4bJ*dcirn=8d8ehvOoWigWriI;i:1hy toaVtehca nT=nru;gtcue':folf8sO;3?tho.I.f_. Square feet Bend Back-Geared Screw Cutting Precision LatheL