CarrLane Jig Fixture

8/12/2019 CarrLane Jig Fixture

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INTRODUCTION TO WORKHOLDING

Over the past century, manufacturing has mae c!nsiera"#e pr!gress$ Ne% machine t!!#s, high

perf!rmance cutting t!!#s, an m!ern manufacturing pr!cesses ena"#e t!ay's inustries t! ma(e parts faster

an "etter than ever "ef!re$ )#th!ugh %!r(h!#ing meth!s have a#s! avance c!nsiera"#y, the "asic princip#es

!f c#amping an #!cating are sti## the same$

HI*TOR+

The first manufacture pr!ucts %ere mae !ne at a time$ ar#y artisans starte %ith #itt#e m!re than ra%

materia#s an a r!ugh iea !f the finishe pr!uct$ They pr!uce each pr!uct piece "y piece, ma(ing each part

iniviua##y an fitting the parts int! the finishe pr!uct$ This pr!cess t!!( time$ -!re!ver, the .ua#ity an

c!nsistency !f pr!ucts varie fr!m !ne artisan t! the ne/t$ )s they %!r(e, ear#y manufacturing pi!neers

rea#i0e the nee f!r "etter meth!s an eve#!pe ne% ieas$

ventua##y, they f!un the secret !f mass pr!ucti!n1 stanari0e parts$ *tanar parts n!t !n#y speee

pr!ucti!n, they a#s! ensure the interchangea"i#ity !f parts$ The iea may "e !"vi!us t!ay, "ut in its time, it

%as rev!#uti!nary$

These stanar parts %ere the (ey t! ena"#ing #ess&s(i##e %!r(ers t! rep#icate the s(i## !f the craftsman !n a

repetitive "asis$ The !rigina# meth! !f achieving c!nsistent part c!nfigurati!n %as the temp#ate$ Temp#ates f!r

#ay!ut, sa%ing, an fi#ing permitte each %!r(er t! ma(e parts t! a stanar esign$ Whi#e ear#y temp#ates %ere

crue, they at #east gave s(i##e %!r(ers a stanar f!rm t! f!##!% f!r the part$ 2ui#ing !n the temp#ate iea,

%!r(ers c!nstructe !ther guies an %!r(h!#ers t! ma(e their 3!"s easier an the resu#ts m!re preicta"#e$

These guies an %!r(h!#ers %ere the ancest!rs !f t!ay's 3igs an fi/tures$

+esteray's %!r(h!#ers ha the same t%! "asic functi!ns as t!ay's1 secure#y h!#ing an accurate#y

#!cating a %!r(piece$ ar#y 3igs an fi/tures may have #ac(e m!ern refinements, "ut they f!##!%e many !f the

same princip#es as t!ay4s %!r(h!#er esigns$

D5INITION*

Often the terms 63ig6 an 6fi/ture6 are c!nfuse !r use interchangea"#y7 h!%ever, there are c#ear

istincti!ns "et%een these t%! t!!#s$ )#th!ugh many pe!p#e have their !%n efiniti!ns f!r a 3ig !r fi/ture, there is!ne universa# istincti!n "et%een the t%!$ 2!th 3igs an fi/tures h!#, supp!rt, an #!cate the %!r(piece$ ) 3ig

h!%ever, guies the cutting t!!#$ ) fi/ture references the cutting t!!#$ The ifferentiati!n "et%een these types !f

%!r(h!#ers is in their re#ati!n t! the cutting t!!#$ )s sh!%n in 5igure 8&8, 3igs use ri## "ushings t! supp!rt an

guie the t!!#$ 5i/tures, 5igure 8&9, use set "#!c(s an thic(ness, !r fee#er, gages t! #!cate the t!!# re#ative t! the

%!r(piece$

5igure 8&8$ ) 3ig guies the cutting t!!#, in this case %ith a "ushing$


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5igure 8&9$ ) fi/ture references the cutting t!!#, in this case %ith a set "#!c($

:igs

The m!st&c!mm!n 3igs are ri## an "!ring 3igs$ These t!!#s are funamenta##y the same$ The ifference #ies

in the si0e, type, an p#acement !f the ri## "ushings$ 2!ring 3igs usua##y have #arger "ushings$ These "ushings

may a#s! have interna# !i# gr!!ves t! (eep the "!ring "ar #u"ricate$ Often, "!ring 3igs use m!re than !ne "ushing

t! supp!rt the "!ring "ar thr!ugh!ut the machining cyc#e$

In the sh!p, ri## 3igs are the m!st&%ie#y use f!rm !f 3ig$ Dri## 3igs are use f!r ri##ing, tapping, reaming

chamfering, c!unter"!ring, c!untersin(ing, an simi#ar !perati!ns$ Occasi!na##y, ri## 3igs are use t! perf!rm

assem"#y %!r( a#s!$ In these situati!ns, the "ushings guie pins, !%e#s, !r !ther assem"#y e#ements$

:igs are further ientifie "y their "asic c!nstructi!n$ The t%! c!mm!n f!rms !f 3igs are !pen an c#!se$

Open 3igs carry !ut !perati!ns !n !n#y !ne, !r s!metimes t%!, sies !f a %!r(piece$ C#!se 3igs, !n the !ther

han, !perate !n t%! !r m!re sies$ The m!st&c!mm!n !pen 3igs are temp#ate 3igs, p#ate 3igs, ta"#e 3igs, san%ich

3igs, an ang#e p#ate 3igs$ Typica# e/amp#es !f c#!se 3igs inc#ue "!/ 3igs, channe# 3igs, an #eaf 3igs$ Other f!rms

!f 3igs re#y m!re !n the app#icati!n !f the t!!# than !n their c!nstructi!n f!r their ientity$ These inc#ue ine/ing

3igs, trunni!n 3igs, an mu#ti&stati!n 3igs$

*pecia#i0e inustry app#icati!ns have #e t! the eve#!pment !f specia#i0e ri## 3igs$ 5!r e/amp#e, the nee

t! ri## precise#y #!cate rivet h!#es in aircraft fuse#ages an %ings #e t! the esign !f #arge 3igs, %ith "ushings

an #iners insta##e, c!nt!ure t! the surface !f the aircraft$ ) p!rta"#e air&fee ri## %ith a "ushing attache t! its

n!se is inserte thr!ugh the #iner in the 3ig an ri##ing is acc!mp#ishe in each #!cati!n$

5i/tures

5i/tures have a much&%ier sc!pe !f app#icati!n than 3igs$ These %!r(h!#ers are esigne f!r app#icati!ns

%here the cutting t!!#s cann!t "e guie as easi#y as a ri##$ With fi/tures, an ege finer, center finer, !r gage

"#!c(s p!siti!n the cutter$ /amp#es !f the m!re&c!mm!n fi/tures inc#ue mi##ing fi/tures, #athe fi/tures, sa%ing

fi/tures, an grining fi/tures$ -!re!ver, a fi/ture can "e use in a#m!st any !perati!n that re.uires a precise

re#ati!nship in the p!siti!n !f a t!!# t! a %!r(piece$

5i/tures are m!st !ften ientifie "y the machine t!!# %here they are use$ /amp#es inc#ue mi## fi/tures !r

#athe fi/tures$ 2ut the functi!n !f the fi/ture can a#s! ientify a fi/ture type$ *! can the "asic c!nstructi!n !f the

t!!#$ Thus, a#th!ugh a t!!# can "e ca##e simp#y a mi## fi/ture, it c!u# a#s! "e further efine as a stra#e&mi##ing,

p#ate&type mi## fi/ture$ -!re!ver, a #athe fi/ture c!u# a#s! "e efine as a raius&turning, ang#e&p#ate #athe fi/ture

The t!!# esigner usua##y ecies the specific ientificati!n !f these t!!#s$


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T!!# !r T!!#ing

The term 6t!!#6 enc!mpasses "!th 3igs an fi/tures$ ssentia##y, it is a generic term escri"ing a %!r(h!#er

%hich is ientifie %ith a part !r machine$ *!metimes 6t!!#6 is use t! refer t! a cutting t!!# !r a machine t!!#, s!

it is imp!rtant t! ma(e c#ear istincti!ns$

W!r(h!#ers

)n!ther term %hich escri"es "!th 3igs an fi/tures is 6%!r(h!#er$6 ) "r!a term, it fre.uent#y ientifies

any evice %hich h!#s, supp!rts, an #!cates a %!r(piece$ In aiti!n t! 3igs an fi/tures, vises, c!##ets, c#amps

an !ther simi#ar evices are a#s! %!r(h!#ers$

;R-)NNT )ND T-;OR)R+ WORKHOLDR*

:igs an fi/tures are m!st !ften f!un %here parts are pr!uce in #arge .uantities, !r pr!uce t! c!mp#e/

specificati!ns f!r a m!erate .uantity$ With the same esign princip#es an #!gic, %!r(h!#ing evices can "e

aapte f!r #imite&pr!ucti!n app#icati!ns$ The ma3!r ifference "et%een permanent an temp!rary %!r(h!#ers

is the c!st


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Genera#&;urp!se W!r(h!#ers

In many instances, the shape !f the part an the machining t! "e perf!rme a##!% f!r the use !f a genera#&

purp!se %!r(h!#er such as a vise, c!##et, !r chuc($ These %!r(h!#ers are aapta"#e t! ifferent machines an

many ifferent parts$

*ince they are n!t part&specific, their versati#ity a##!%s f!r repeate use !n a variety !f ifferent !r #imite&

pr!ucti!n runs$ The c!st !f these %!r(h!#ers %!u# usua##y "e average !ver years an might n!t even "e a

fact!r in 3!"&c!st ca#cu#ati!ns$ The genera#&purp!se nature !f these %!r(h!#ers necessitates a higher #eve# !f

!perat!r care an attenti!n t! maintain c!nsistency an accuracy$ 5!r these reas!ns, genera#&purp!se%!r(h!#ers are n!t preferre f!r #engthy pr!ucti!n runs$

-!u#ar 5i/tures

-!u#ar fi/tures achieve many !f the avantages !f a permanent t!!# using !n#y a temp!rary setup$ Depicte

in 5igure 8&>, these %!r(h!#ers c!m"ine ieas an e#ements !f permanent an genera#&purp!se %!r(h!#ing$

5igure 8&>$ -!u#ar %!r(h!#ers c!m"ine ieas an e#ements !f "!th permanent an temp!rary %!r(h!#ing t! ma(e ine/pensive&yet&ura"#e %!r(h!#ers$

The primary avantage !f m!u#ar fi/tures is that a t!!# %ith the "enefits !f permanent t!!#ing ?setup

reucti!n, ura"i#ity, pr!uctivity impr!vements, an reuce !perat!r ecisi!n&ma(ing@ can "e "ui#t fr!m a set !f

stanar c!mp!nents$ The fi/ture can "e isassem"#e %hen the run is c!mp#ete, t! a##!% the reuse !f the

c!mp!nents in a ifferent fi/ture$ )t a #ater time the !rigina# can "e reai#y rec!nstructe fr!m ra%ings

instructi!ns, an ph!t!graphic rec!rs$ This reuse ena"#es the c!nstructi!n !f a c!mp#e/, high&precisi!n t!!

%ith!ut re.uiring the c!rresp!ning eicati!n !f the fi/ture c!mp!nents$

5igure 8&A sh!%s h!% m!u#ar fi/turing fits int! the hierarchy !f %!r(h!#ing !pti!ns, ran(ing "e#!%

permanent fi/turing yet a"!ve genera#&purp!se %!r(h!#ers$ Birtua##y every manufacturer has g!! app#icati!ns

f!r each !f these three !pti!ns at !ne time !r an!ther$


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5igure 8&A$ The hierarchy !f %!r(h!#ing !pti!ns$

D*IGN CON*IDR)TION*

The principa# c!nsierati!ns %hen ch!!sing am!ng %!r(h!#er varieties fa## int! three genera# categ!ries1

t!!#ing c!st, t!!#ing etai#s, an t!!#ing !perati!n$ )#th!ugh each !f these categ!ries is separate here, in

practice they are interepenent$ The f!##!%ing are s!me esign ifferences an c!nsierati!ns f!r permanentgenera#&purp!se, an m!u#ar %!r(h!#ers$

T!!#ing C!sts

The t!ta# c!st !f any 3ig !r fi/ture is fre.uent#y the ma3!r area !f c!nsierati!n in many %!r(h!#er esigns$

)#th!ugh initia# c!st is a ma3!r e#ement, it sh!u# n!t "e the "asis f!r accepting !r re3ecting any t!!#ing !pti!n$

) m!re&pr!per ec!n!mic eva#uati!n !f the %!r(h!#er esign ta(es int! c!nsierati!n many !ther fact!rs

)s iscusse previ!us#y, permanent fi/tures have istinct avantages in the pr!ucti!n !f high&v!#ume an high&

precisi!n parts$ They a#s! typica##y reuce machine setup time, machine cyc#e time, an the #eve# !f !perat!r s(i#

re.uire t! pr!uce satisfact!ry .ua#ity !utput$ Over a #!ng pr!ucti!n run, !r a series !f runs in the #ife !f a t!!#,

the average c!st !f the t!!# per piece pr!uce can "e .uite #!%$

Genera#&purp!se %!r(h!#ers are m!re e/pensive than temp!rary t!!#s in m!st cases, "ut their uti#ity an

f#e/i"i#ity !ften a##!% these %!r(h!#ers t! "e regare as a capita# c!st t! "e am!rti0e !ver a peri! !f time

%ith!ut regar t! actua# usage$ *imi#ar#y, m!u#ar fi/turing is typica##y a capita# investment t! "e am!rti0e !ver a

set #ifespan, %ith an average c!st assigne t! usage f!r each anticipate 3!"$

)n!ther c!st t! "e c!nsiere is %!r(h!#er isp!siti!n$ ;ermanent fi/tures re.uire st!rage an

maintenance t! (eep them avai#a"#e f!r their ne/t use$ Genera#&purp!se t!!#s are reuse e/tensive#y, "ut sti## incur

s!me c!sts f!r maintenance an st!rage$ *imi#ar#y, m!u#ar fi/tures %i## "e isassem"#e, an the c!mp!nents

maintaine, st!re, an reuse fre.uent#y$


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T!!#ing Detai#s

T!!#ing etai#s are the !vera## c!nstructi!n characteristics an specia# features inc!rp!rate int! the 3ig !r

fi/ture$ ;ermanent %!r(h!#ers are esigne an "ui#t t! #ast #!nger than temp!rary %!r(h!#ers$ *!, permanent

3igs an fi/tures usua##y c!ntain m!re&e#a"!rate parts an features than temp!rary %!r(h!#ers$

There are severa# !ther ifferences "et%een permanent an temp!rary %!r(h!#ers in this area$ These

inc#ue the type an c!mp#e/ity !f the iniviua# t!!#ing e#ements, the e/tent !f sec!nary machining an

finishing !perati!ns !n the t!!#, the t!!#&esign pr!cess, an the am!unt !f etai# in the %!r(h!#er ra%ings

*ince the e#ements f!r m!u#ar %!r(h!#ers are usua##y part !f a c!mp#ete set, !r system, !n#y rare#y %i##aiti!na# cust!m c!mp!nents nee t! "e mae$

;ermanent %!r(h!#ers c!ntain ifferent c!mmercia# t!!#ing c!mp!nents "ase !n e/pecte t!!# usage

;ermanent 3igs intene f!r a high&v!#ume ri##ing !perati!n, f!r e/amp#e, !ften use a rene%a"#e "ushing an #iner

"ushing t!gether$ ) thr!%a%ay 3ig f!r a sma##er pr!ucti!n run !ften uses a simp#e press&fit "ushing$

The sec!nary !perati!ns n!rma##y ass!ciate %ith t!!#ing inc#ue harening, grining, an simi#ar

!perati!ns t! finish the %!r(h!#er$ Usua##y, permanent %!r(h!#ers are harene an gr!un t! assure their

accuracy !ver a #!ng pr!ucti!n run$ *ince they are intene !n#y f!r sh!rt pr!ucti!n runs, thr!%a%ay 3igs an

fi/tures ! n!t re.uire these !perati!ns$ )n!ther sec!nary !perati!n fre.uent#y perf!rme !n permanent t!!#s

"ut n!t temp!rary t!!#s, is app#ying a pr!tective finish, such as "#ac( !/ie, chr!me p#ating, !r ename# paint$

In esigning a permanent %!r(h!#er, the esigner !ften ma(es etai#e engineering ra%ings t! sh!% the

t!!#r!!m e/act#y %hat must "e !ne t! "ui# the %!r(h!#er$ With temp!rary %!r(h!#ers, the esign ra%ings

are !ften sent t! the t!!#r!!m as simp#e freehan s(etches$

;ermanent t!!#s are n!rma##y esigne f!r #!ng&term use$ This "eing the case, the ra%ings an engineering

ata f!r the permanent 3ig !r fi/ture then "ec!me a permanent rec!r$ With m!u#ar %!r(h!#ers, the esigner

may either c!nstruct ra%ings !r specify "ui#ing the %!r(h!#er irect#y ar!un the part$ Here !n#y a parts #ist

an ph!t!graphs !r vie! tape are (ept as a permanent rec!r$

Certain %!r(h!#ing app#icati!ns re.uire specia# fi/ture characteristics$ 5!r e/amp#e, a particu#ar#y c!rr!sive

envir!nment may re.uire stain#ess stee# c!mp!nents an c#amps t! e#iver a satisfact!ry #ife cyc#e$ In !ther

cases, varia"#e %!r(piece imensi!ns, as in a casting, necessitate c#amping evices %hich can c!mpensate f!

these variati!ns$ )ppearance !f a finishe part might re.uire the use !f ny#!n, p#astic, !r ru""er c!ntact p!ints t!

pr!tect the part$

*imi#ar#y, the se#ecti!n !f t!!#ing etai#s can enhance the pr!uctivity !f s!me permanent t!!#s$ 5!r

e/amp#e, uti#i0ing sma## hyrau#ic c#amps may a##!% #!aing many parts !n a %!r(h!#er ue t! the c!mpactness

!f the esign$ This %!u# enhance pr!uctivity "y reucing #!a


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5igure 8&$ ) c!m"inati!n ri## 3ig


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Lathe fi/tures Cy#inrica#&grining fi/tures

Irregu#ar&*urface -achining 2an&sa%ing fi/tures /terna#&"r!aching fi/turesINTRN)L&-)CHINING );;LIC)TION*1Cy#inrica#& an Irregu#ar&H!#e -achining Dri## 3igs 2!ring 3igs #ectrica#&ischarge&machining fi/tures ;unching fi/tures

Interna#&"r!aching fi/turesNON&-)CHINING );;LIC)TION*1)ssem"#y We#ing fi/tures -echanica#&assem"#y fi/tures ?Riveting, stap#ing, stitching, pinning, etc$@ *!#ering fi/tures

Inspecti!n -echanica#&inspecti!n fi/tures Optica#&inspecti!n fi/tures #ectr!nic&inspecti!n fi/tures

5inishing ;ainting fi/tures ;#ating fi/tures ;!#ishing fi/tures

Lapping fi/tures H!ning fi/tures

-isce##ane!us Lay!ut temp#ates Testing fi/tures Heat&treating fi/tures

5igure 8&F$ Typica# app#icati!ns !f 3igs an fi/tures


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CR)TIB TOOL D*IGN

The first step in esigning any 3ig !r fi/ture is a th!r!ugh eva#uati!n !f its functi!na# re.uirements$ The g!a

is t! fin a "a#ance c!m"inati!n !f esign characteristics at a reas!na"#e c!st$ The part itse#f, pr!cessing

t!!#ing, an machine&t!!# avai#a"i#ity may a## affect the e/tent !f p#anning neee$ ;re#iminary ana#ysis may ta(e

fr!m a fe% h!urs up t! severa# ays f!r m!re&c!mp#icate esigns$

T! esign a %!r(h!#er, "egin %ith a #!gica# an systematic p#an$ With a c!mp#ete ana#ysis, very fe% esign

pr!"#ems !ccur$ W!r(h!#er pr!"#ems !ccur %hen esign re.uirements are f!rg!tten !r unerestimate$ N!

specific f!rmu#a !r meth! %!r(s f!r every esign, "ut the esigner can emp#!y a e#i"erate an #!gica# system in

the initia# p#anning an esign$

T!!# esign is essentia##y an e/ercise in pr!"#em s!#ving$ Creative pr!"#em s!#ving can "e escri"e as a

five&step pr!cess1 8@ Ientifying an efining the pr!"#em7 9@ Gathering an ana#y0ing inf!rmati!n7 =@

2rainst!rming f!r a#ternative s!#uti!ns7 >@ Ch!!sing the "est s!#uti!n7 A@ Imp#ementing the s!#uti!n$ This five&step

pr!cess aapte t! 3ig&an&fi/ture esigns is sh!%n in 5igure 9&8$

5igure 9&8$ 5ive steps that ma(e up a g!!, systematic t!!#&esign pr!cess$


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D5INING RUIR-NT*

The first step in the t!!#&esign pr!cess sh!u# "e t! c#ear#y state the pr!"#em t! "e s!#ve, !r nees t! "e

met$ These re.uirements sh!u# "e state as "r!a#y as p!ssi"#e, "ut specifica##y en!ugh t! efine the sc!pe !f

the esign pr!3ect$

The ne% t!!#ing might "e re.uire either f!r first&time pr!ucti!n !f a ne% pr!uct, !r t! impr!ve pr!ucti!n

!f an e/isting part$ When impr!ving an e/isting 3!", the g!a# might "e greater accuracy, faster cyc#e times, !r

"!th$ T!!#ing might "e esigne f!r !ne part, !r an entire fami#y$

T!!# esign is an integra# part !f the pr!uct&p#anning pr!cess, interacting %ith pr!uct esign

manufacturing, an mar(eting$ T! reach an !ptimum s!#uti!n, a## f!ur !f these gr!ups nee t! %!r( t!gether

c!ncurrent#y$

G)THRING )ND )N)L+ING IN5OR-)TION

In the sec!n esign phase, a## ata is c!##ecte an assem"#e f!r eva#uati!n$ The main s!urces !f

inf!rmati!n are the part print, pr!cess sheets, an machine specificati!ns$ When c!##ecting this inf!rmati!n, ma(e

sure that part !cuments an rec!rs are current$ 5!r e/amp#e, verify that the sh!p print is the current revisi!nan the pr!cessing inf!rmati!n is up t! ate$ Chec( %ith the pr!uct&esign epartment f!r pening part

revisi!ns$

)n imp!rtant part !f the eva#uati!n pr!cess is n!teta(ing$ C!mp#ete, accurate n!tes a##!% the esigner t!

rec!r imp!rtant inf!rmati!n$ )## ieas, th!ughts, !"servati!ns, an any !ther ata a"!ut the part !r t!!# are then

avai#a"#e f!r #ater reference$ It is a#%ays "etter t! have t!! many ieas a"!ut a particu#ar esign than n!t en!ugh$

G!! n!tes a#s! minimi0e the chance that g!! ieas %i## "e #!st$

5!ur categ!ries !f esign c!nsierati!ns nee t! "e ta(en int! acc!unt at this time1 the %!r(piece

manufacturing !perati!ns, e.uipment, an pers!nne#$ ) chec(#ist is sh!%n in 5igure 9&9$


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CHCKLI*T 5OR D*IGN CON*IDR)TION*

5igure 9&9$ C!nsierati!ns %hen gathering an ana#y0ing inf!rmati!n f!r a t!!# esign

These categ!ries, %hi#e separate#y c!vere here, are actua##y interepenent$ ach is an integra# part !f the

eva#uati!n phase an must "e th!r!ugh#y th!ught !ut "ef!re "eginning the %!r(h!#er esign$

W!r(piece C!nsierati!ns

W!r(piece specificati!ns are usua##y the m!st&imp!rtant fact!rs an have the #argest inf#uence !n the

%!r(h!#er's fina# esign$ Typica##y these c!nsierati!ns inc#ue the si0e an shape !f the part, the accuracyre.uire, the pr!perties !f the part materia#, #!cating an c#amping surfaces, an the num"er !f pieces$

Operati!n C!nsierati!ns

These c!nsierati!ns inc#ue the type !f !perati!ns re.uire f!r the part, the num"er !f !perati!ns

perf!rme, the se.uence !f !perati!ns, inspecti!n re.uirements, an time restricti!ns$

.uipment C!nsierati!ns

.uipment c!nsierati!ns c!ntr!# the type !f e.uipment neee t! machine, assem"#e, an inspect a part$

Often the avai#a"#e e.uipment etermines %hether the %!r(h!#er is esigne f!r sing#e !r mu#tip#e parts$ )


12/36

pr!cess engineer s!metimes se#ects the e.uipment f!r re.uire functi!ns "ef!re the t!!# esigner "egins the

esign$ *ti##, the t!!# esigner sh!u# verify e.uipment ch!ices f!r each !perati!n$

) vertica# mi##ing machine, f!r e/amp#e, is %e## suite f!r s!me ri##ing !perati!ns$ 2ut f!r !perati!ns that

re.uire a ri## 3ig, a ri## press is the m!st&c!st&effective machine t!!#$ Typica##y, e.uipment criteria inc#ue the

f!##!%ing fact!rs1 types an si0es !f machine t!!#s, inspecti!n e.uipment, scheu#ing, cutting t!!#s, an genera

p#ant faci#ities$

;ers!nne# C!nsierati!ns

;ers!nne# c!nsierati!ns ea# %ith the en user, !r !perat!r, !f the e.uipment$ -!st specia# t!!#s are

esigne t! "e use "y sh!p pers!nne#, s! the esign !f any %!r(h!#er must "e mae %ith the !perat!r in min

The first an m!st&imp!rtant c!nsierati!n in this phase is safety$ N! t!!# sh!u# ever "e esigne %ith!ut

c!mp#ete safety in min$

)iti!na# fact!rs typica##y c!nsiere in this categ!ry are !perat!r fatigue, efficiency, ec!n!my !f m!ti!n,

an the spee !f the !perati!n$ The esigner must a#s! (n!% an unerstan the genera# aspects !f esign safety

an a## appr!priate g!vernment an c!mpany safety ru#es an c!es$

DBLO;ING *BR)L O;TION*

The thir phase !f the t!!#&esign pr!cess re.uires the m!st creativity$ ) typica# %!r(piece can "e #!catean c#ampe many ifferent %ays$ )n imp!rtant strategy f!r successfu# t!!# esign is "rainst!rming f!r severa

g!! t!!#ing a#ternatives, n!t 3ust ch!!sing !ne path right a%ay$

During this phase, the esigner's g!a# sh!u# "e aing !pti!ns, n!t iscaring them$ In the interest !f

ec!n!my, a#ternative esigns sh!u# !n#y "e eve#!pe far en!ugh t! ma(e sure they are feasi"#e, an t! ! a

c!st estimate$

2rainst!rming f!r Ieas

The esigner usua##y starts %ith at #east three !pti!ns1 permanent, m!u#ar, an genera#&purp!se

%!r(h!#ing, as seen in 5igure 9&=$ ach !f these !pti!ns has many c#amping an #!cating !pti!ns !f its !%n$ The

m!re stanar #!cating an c#amping evices that a esigner is fami#iar %ith, the m!re creative he can "e$

5igure 9&=$ -!st t!!#&esign pr!3ects "egin %ith three genera# !pti!ns1 permanent, m!u#ar, an genera#&purp!se %!r(h!#ing$ Differenmeth!s !f #!cating an c#amping further increase the num"er !f !pti!ns$

There is se#!m !n#y !ne %ay t! #!cate a part$ Opti!ns inc#ue f#at e/teri!r surfaces ?machine an

unmachine@, cy#inrica# an curve e/teri!r surfaces, an interna# features ?such as h!#es an s#!ts@$ The ch!ice

!f stanar #!cating evices is .uite e/tensive$


13/36


14/36

5igure 9&>$ Itemi0e #isting !f c!mp!nents f!r a %!r(h!#er$

The ne/t step is ca#cu#ating the c!st !f materia# an #a"!r f!r each t!!# e#ement$ Once again, it is imp!rtant t!

have an !rer#y system !f #isting the ata$ 5irst #ist the c!st !f each c!mp!nent, then itemi0e the !perati!ns

neee t! m!unt, machine, !r assem"#e that c!mp!nent$ Once these steps are #iste, estimate the time re.uire

f!r each !perati!n f!r each c!mp!nent, then mu#tip#y "y the #a"!r rate$ This am!unt sh!u# then "e ae t! thec!st !f the c!mp!nents an the c!st !f esign t! fin the estimate c!st !f the %!r(h!#er$

5!r m!u#ar fi/tures, t!ta# c!mp!nent c!st sh!u# "e am!rti0e !ver the system's typica# #ifetime$ )#th!ugh

s!me%hat ar"itrary, iviing t!ta# c!mp!nent c!st "y 8JJ ?8J uses per year, f!r ten years@ gives a fair estimate$

C!st C!mparis!n

The t!ta# c!st t! manufacture a part is the sum !f per&piece run c!st, setup c!st, an t!!#ing c!st$ /presse

as a f!rmu#a1

The f!##!%ing e/amp#e sh!%s three t!!#ing !pti!ns f!r the part in 5igure 9&=1 8@ a m!u#ar fi/ture7 9@ a

permanent fi/ture7 =@ a permanent fi/ture using hyrau#ic p!%er %!r(h!#ing$ ach varia"#e in the c!st e.uati!n is

e/p#aine separate#y "e#!%$

Run Cost.This is the varia"#e c!st per piece t! pr!uce a part, at sh!p #a"!r rate ?materia# c!st !es n!t

nee t! "e inc#ue as #!ng as it is the same f!r a## fi/turing !pti!ns@$ In !ur e/amp#e, run c!sts f!r the permanent

an m!u#ar fi/tures are the same, %hi#e p!%er %!r(h!#ing #!%ers c!sts "y impr!ving cyc#e time an reucing

scrap$


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Setup Cost.This is the c!st t! retrieve a fi/ture, set it up !n the machine, an return it t! st!rage after use

The permanent fi/ture is fastest t! set up, the p!%er&%!r(h!#ing fi/ture is s#ight#y s#!%er ue t! hyrau#ic

c!nnecti!ns, an the m!u#ar fi/ture is s#!%est ue t! the assem"#y re.uire$

Lot Size.This is the average .uantity manufacture each time the fi/ture is set up$ In !ur e/amp#e, #!t si0e is

the same f!r a## three !pti!ns$

Initial Tooling Cost.This is the t!ta# c!st !f #a"!r p#us materia# t! esign an "ui# a fi/ture ?as e/p#aine in

the previ!us secti!n@$ The m!u#ar fi/ture is #east e/pensive "ecause c!mp!nents can "e reuse, the permanent

fi/ture ne/t, an the hyrau#ic fi/ture m!st e/pensive$

Total Quantity Over Tooling Lifetime. This .uantity, the #ast remaining varia"#e, is the #esser !f 8@ t!ta

anticipate pr!ucti!n .uantity an 9@ the .uantity that can "e pr!uce "ef!re the t!!#ing %ears !ut$ The

f!##!%ing resu#ts are !"taine "y eva#uating the c!st&per&part f!rmu#a at ifferent #ifetime .uantities1

5!r a !ne&time run !f 8JJ pieces, the m!u#ar fi/ture is c#ear#y the m!st ec!n!mica#$ If ten runs ?8,JJJ pieces@

are e/pecte, the permanent fi/ture is "est$ 5!r 9,AJJ pieces an a"!ve, the p!%er %!r(h!#ing fi/ture %!u# "e

the "est ch!ice$ This ana#ysis assumes that a## n!nec!n!mic fact!rs are e.ua#$


16/36

I-;L-NTING TH D*IGN

The fina# phase !f the t!!#&esign pr!cess c!nsists !f turning the ch!sen esign appr!ach int! rea#ity$ 5ina

etai#s are ecie, fina# ra%ings are mae, an the t!!#ing is "ui#t an teste$

Guie#ines f!r c!n!mica# Design

The f!##!%ing guie#ines sh!u# "e c!nsiere uring the fina#&esign pr!cess$ These ru#es are a mi/ !f

practica# c!nsierati!ns, s!un esign practices, an c!mm!n sense$ )pp#icati!n !f these ru#es ma(es the

%!r(h!#er #ess c!st#y, an impr!ves its efficiency an !perati!n$

Use Standard Tooling Components. The ec!n!mies !f stanari0e parts app#y t! t!!#ing c!mp!nents as

%e## as t! manufacture pr!ucts$ *tanar t!!#ing c!mp!nents, reai#y avai#a"#e fr!m y!ur inustria# supp#ier,

inc#ue c#amps, #!cat!rs, supp!rts, stus, nuts, pins, an a h!st !f !ther e#ements$ -!st esigners %!u# never

thin( !f having the sh!p ma(e cap scre%s, "!#ts, !r nuts f!r a %!r(h!#er$ 5!r the same reas!n, virtua##y n!

stanar t!!#ing c!mp!nents sh!u# "e mae in&h!use$ The first ru#e !f ec!n!mic esign is1 Never "ui# any

c!mp!nent y!u can "uy$ C!mmercia##y avai#a"#e t!!#ing c!mp!nents are manufacture in #arge .uantities f!r

much greater ec!n!my$

La"!r is usua##y the #argest c!st e#ement in the "ui#ing !f any %!r(h!#er$ *tanar t!!#ing c!mp!nents are

!ne %ay t! cut #a"!r c!sts$ )#%ays #!!( f!r ne% %!r(h!#ing pr!ucts t! ma(e esigns simp#er an #ess

e/pensive$ 2r!%se thr!ugh cata#!gs an maga0ines t! fin ne% pr!ucts an app#icati!n ieas$ In m!st casesthe c!st !f "uying a c!mp!nent is #ess than 9J !f the c!st !f ma(ing it$

Use Prefinished aterials.;refinishe an pref!rme materia#s sh!u# "e use %here p!ssi"#e t! #!%er

c!sts an simp#ify c!nstructi!n$ These materia#s inc#ue precisi!n&gr!un f#at st!c(, ri## r!, structura# secti!ns

cast t!!#ing secti!ns, precast t!!# "!ies, t!!#ing p#ates, an !ther stanar pref!rme materia#s$ Inc#uing these

materia#s in a esign "!th reuces the esign time an #!%ers the #a"!r c!st$

#iminate Unneee 5inishing Operati!ns$ 5inishing !perati!ns sh!u# never "e perf!rme f!r c!smetic

purp!ses$ -a(ing a t!!# #!!( "etter can !ften !u"#e the c!st !f the fi/ture$ Here are a fe% suggesti!ns t! (eep in

min %ith regar t! finishing !perati!ns1

-achine !n#y the areas imp!rtant t! the functi!n an !perati!n !f the t!!#$ 5!r e/amp#e, ! n!t machine

the eges !f a "asep#ate$ :ust rem!ve the "urrs$

Haren !n#y th!se areas !f the t!!# su"3ect t! %ear$

Grin !n#y the areas !f the fi/ture %here necessary f!r the !perati!n !f the t!!#$

!eep Toleran"es #s Li$eral #s Possi$le. The m!st&c!st&effective t!!#ing t!#erance f!r a #!cat!r is

appr!/imate#y =J t! AJ !f the %!r(piece's t!#erance$ Tighter t!#erances n!rma##y a e/tra c!st t! the t!!# %ith

#itt#e "enefit t! the pr!cess$ Where necessary, tighter t!#erances can "e use, "ut a tighter t!#erance !es n!t

necessari#y mean a "etter t!!#, !n#y a m!re e/pensive t!!#$

Simplify Tooling Operation.#a"!rate esigns !ften a #itt#e !r n!thing t! the functi!n !f the 3ig !r fi/ture$

C!mp#e/ mechanica# c#amping systems, f!r e/amp#e, are !ften e#a"!rate an unneee esigns$ -!re !ften, a

p!%er c#amp c!u# ! the same 3!" at a fracti!n !f the c!st$ C!smetic etai#s are an!ther e/amp#e !f #itt#e gaine

f!r the m!ney spent$ These etai#s may ma(e the t!!# #!!( g!!, "ut se#!m 3ustify the ae c!st$

Keep the functi!n an !perati!n !f a %!r(h!#er as simp#e as p!ssi"#e$ The #i(e#ih!! !f "rea(!%ns an

!ther pr!"#ems increases %ith c!mp#e/ esigns$ These pr!"#ems mu#tip#y %hen m!ving parts are ae t! the

esign$ -isa#ignment, inaccuracy, %ear, an ma#functi!ns cause "y chips an e"ris can cause many pr!"#ems

in the "est t!!# esigns$

Reucing esign c!mp#e/ity a#s! reuces misunerstanings "et%een the esigner an the machine

!perat!r$ Whenever p!ssi"#e, a %!r(h!#er's functi!n an !perati!n sh!u# "e !"vi!us t! the !perat!r %ith!ut

instructi!ns$


17/36

-anua# Dra%ings

Once s(etches an the "asic %!r(h!#er esign have "een c!mp#ete, fina# engineering ra%ings can "e

prepare$ C!pies !f the engineering ra%ings, a#s! ca##e sh!p prints, are use "y the t!!#r!!m t! "ui# the

%!r(h!#er$

-anua# ra%ing is the pr!cess !f c!nstructing engineering ra%ings "y han !n a ra%ing "!ar$ The

easiest %ay t! reuce ra%ing time is "y simp#ifying the ra%ing$ W!rs !r sym"!#s sh!u# "e use in p#ace !f

ra%n etai#s %here practica#$ )## e/tra !r unnecessary vie%s, pr!3ecti!ns, an etai#s sh!u# "e e#iminate fr!m

the ra%ing$ This cuts the time spent ra%ing etai#s that a #itt#e t! the meaning !f the ra%ing$

Dra%ing a c!mp#ete c#amp assem"#y, f!r e/amp#e, as very #itt#e t! the c!mp#ete esign$ *imp#y sh!%ing

the n!se !f the c#amp in its pr!per re#ati!n t! the %!r(piece, a#!ng %ith specifying its part num"er, c!nveys the

same inf!rmati!n in a fracti!n !f the time$

C!mputer&)ie Design

C!mputers are rapi#y rep#acing ra%ing "!ars as the preferre t!!# f!r preparing engineering ra%ings

)#m!st every area !f esign is affecte "y the c!mputer$ C!mputers, fr!m #arge mainframes t! micr!c!mputers

are "ec!ming stanar e.uipment in many esign epartments$

) stanar t!!#ing #i"rary, sh!%n in 5igure 9&A, is !ften use t! a the fi/turing c!mp!nents an e#ements

t! the t!!# ra%ing$ Using a stanar #i"rary in esigning the %!r(h!#er ramatica##y reuces ra%ing time$ )#

c!mp!nents are ra%n t! fu## sca#e in a variety !f vie%s$ ach c!mp!nent can "e ca##e up fr!m the #i"rary an

p#ace !n the ra%ing %here it is re.uire$

5igure 9&A$ Using a stanar C)D t!!#ing #i"rary can ramatica##y reuce esign time$

) C)D system is a#s! s!metimes usefu# uring the initia# phase !f eve#!ping numer!us t!!#ing !pti!ns

C!mputer&aie esign is s!metimes faster than s(etching "y han, especia##y %hen etai#e c!st estimates are

re.uire$

2ui#ing an Testing the W!r(h!#er

Once ra%ings have "een th!r!ugh#y chec(e, the ne/t step is "ui#ing the actua# %!r(h!#er$ During the

"ui#ing stage, the esigner sh!u# ensure the t!!#r!!m (n!%s e/act#y %hat must "e !ne %hen ma(ing the t!!#

2y peri!ica##y chec(ing %ith the t!!#ma(ers, the esigner can he#p e#iminate any p!ssi"#e misunerstanings

an spee the "ui#ing pr!cess$ If there are any ifficu#ties %ith the esign, the esigner an t!!#ma(er, %!r(ing

t!gether, can s!#ve the pr!"#ems %ith a minimum !f #!st time$

)fter the t!!# is c!mp#ete an inspecte, the #ast step is t!!# try!ut$ The %!r(h!#er is set up !n the

machine t!!# an severa# parts are run$ The esigner sh!u# "e !n han t! he#p s!#ve any pr!"#ems$ When the

t!!# pr!ves itse#f in this phase, it is reay f!r pr!ucti!n$


18/36


19/36

The evices that restrict a %!r(piece's m!vement are the #!cat!rs$ The #!cat!rs, theref!re, must "e str!ng

en!ugh t! maintain the p!siti!n !f the %!r(piece an t! resist the cutting f!rces$ This fact a#s! p!ints !ut a

crucia# e#ement in %!r(h!#er esign1 #!cat!rs, n!t c#amps, must h!# the %!r(piece against the cutting f!rces$

L!cat!rs pr!vie a p!sitive st!p f!r the %!r(piece$ ;#ace against the st!p, the %!r(piece cann!t m!ve

C#amps, !n the !ther han, re#y !n#y up!n fricti!n "et%een the c#amp an the c#ampe surface t! h!# the

%!r(piece$ *ufficient f!rce c!u# m!ve the %!r(piece$ C#amps are !n#y intene t! h!# the %!r(piece against the

#!cat!rs$

5!rms !f L!cati!n

There are three genera# f!rms !f #!cati!n1 p#ane, c!ncentric, an raia#$ ;#ane #!cat!rs #!cate a %!r(piece

fr!m any surface$ The surface may "e f#at, curve, !r have an irregu#ar c!nt!ur$ In m!st app#icati!ns, p#ane&

#!cating evices #!cate a part "y its e/terna# surfaces, 5igure =&9a$ C!ncentric #!cat!rs, f!r the m!st part, #!cate a

%!r(piece fr!m a centra# a/is$ This a/is may !r may n!t "e in the center !f the %!r(piece$ The m!st&c!mm!n type

!f c!ncentric #!cati!n is a #!cating pin p#ace in a h!#e$ *!me %!r(pieces, h!%ever, might have a cy#inrica

pr!3ecti!n that re.uires a #!cating h!#e in the fi/ture, as sh!%n in 5igure =&9"$ The thir type !f #!cati!n is raia#

Raia# #!cat!rs restrict the m!vement !f a %!r(piece ar!un a c!ncentric #!cat!r, 5igure =&9c$ In many cases,

#!cating is perf!rme "y a c!m"inati!n !f the three #!cati!na# meth!s$

5igure =&9$ The three f!rms !f #!cati!n1 p#ane, c!ncentric, an raia#$

L!cating fr!m /terna# *urfaces

5#at surfaces are c!mm!n %!r(piece features use f!r #!cati!n$ L!cating fr!m a f#at surface is a f!rm !f

p#ane #!cati!n$ *upp!rts are the principa# evices use f!r this #!cati!n$ The three ma3!r f!rms !f supp!rts are

s!#i, a3usta"#e, an e.ua#i0ing, 5igure =&=$


20/36

5igure =&=$ *!#i, a3usta"#e, an e.ua#i0ing supp!rts #!cate a %!r(piece fr!m a f#at surface$

*!#i supp!rts are fi/e&height #!cat!rs$ They precise#y #!cate a surface in !ne a/is$ Th!ugh s!#i supp!rts

may "e machine irect#y int! a t!!# "!y, a m!re&ec!n!mica# meth! is using insta##e supp!rts, such as rest

"utt!ns$

)3usta"#e supp!rts are varia"#e&height #!cat!rs$ Li(e s!#i supp!rts, they %i## a#s! precise#y #!cate a surface

in !ne a/is$ These supp!rts are use %here %!r(piece variati!ns re.uire a3usta"#e supp!rt t! suit ifferent

heights$ These supp!rts are use main#y f!r cast !r f!rge %!r(pieces that have uneven !r irregu#ar m!unting

surfaces$

.ua#i0ing supp!rts are a f!rm !f a3usta"#e supp!rt use %hen a c!mpensating supp!rt is re.uire

)#th!ugh these supp!rts can "e fi/e in p!siti!n, in m!st cases e.ua#i0ing supp!rts f#!at t! acc!mm!ate

%!r(piece variati!ns$ )s !ne sie !f the e.ua#i0ing supp!rt is epresse, the !ther sie raises the same am!unt

t! maintain part c!ntact$ In m!st cases a3usta"#e an e.ua#i0ing supp!rts are use a#!ng %ith s!#i supp!rts$

L!cating a %!r(piece fr!m its e/terna# eges is the m!st&c!mm!n #!cating meth!$ The "!tt!m, !r primary

#!cating surface is p!siti!ne !n three supp!rts, "ase !n the ge!metry princip#e that three p!ints are neee t!

fu##y efine a p#ane$ T%! a3acent eges, usua##y perpenicu#ar t! each !ther, are then use t! c!mp#ete the

#!cati!n$

The m!st&c!mm!n %ay t! #!cate a %!r(piece fr!m its e/terna# pr!fi#e is the =&9&8, !r si/&p!int, #!cati!na

meth!$ With this meth!, si/ iniviua# #!cat!rs reference an restrict the %!r(piece$

)s sh!%n in 5igure =&>, three #!cat!rs, !r supp!rts, are p#ace uner the %!r(piece$ The three #!cat!rs are

usua##y p!siti!ne !n the primary #!cating surface$ This restricts a/ia# m!vement !%n%ar, a#!ng the &0 a/is ?@an raia##y a"!ut the / ?F an M@ an y ? an 8J@ a/es$ T!gether, the three #!cat!rs restrict five egrees !f

free!m$


21/36

5igure =&>$ Three supp!rts !n the primary #!cating surface restrict five egrees !f free!m$

The ne/t t%! #!cat!rs are n!rma##y p#ace !n the sec!nary #!cating surface, as sh!%n in 5igure =&A$ They

restrict an aiti!na# three egrees !f free!m "y arresting the a/ia# m!vement a#!ng the y a/is ?=@ an the

raia# m!vement a"!ut the 0 ?88 an 89@ a/is$

5igure =&A$ )ing t%! #!cat!rs !n a sie restricts eight egrees !f free!m$

The fina# #!cat!r, sh!%n in 5igure =&, is p!siti!ne at the en !f the part$ It restricts the a/ia# m!vement in

!ne irecti!n a#!ng the &/ a/is$ T!gether, these si/ #!cat!rs restrict a t!ta# !f nine egrees !f free!m$ The

remaining three egrees !f free!m ?8, >, an A@ %i## "e restricte "y the c#amps$

5igure =&$ )ing a fina# #!cat!r t! an!ther sie restricts nine egrees !f free!m, c!mp#eting the =&9&8 #!cati!n$

)#th!ugh cy#inrica# rest "utt!ns are the m!st&c!mm!n %ay !f #!cating a %!r(piece fr!m its e/terna# pr!fi#e,

there are a#s! !ther evices use f!r this purp!se$ These evices inc#ue f#at&sie #!cat!rs, vee #!cat!rs, nest

#!cat!rs an a3usta"#e #!cat!rs$


22/36

L!cating fr!m Interna# *urfaces

L!cating a %!r(piece fr!m an interna# iameter is the m!st&efficient f!rm !f #!cati!n$ The primary features

use f!r this f!rm !f #!cati!n are iniviua# h!#es !r h!#e patterns$ Depening !n the p#acement !f the #!cat!rs,

either c!ncentric, raia#, !r "!th&c!ncentric&an&raia# #!cati!n are acc!mp#ishe %hen #!cating an interna

iameter$ ;#ane #!cati!n is a#s! pr!vie "y the p#ate use t! m!unt the #!cat!rs$

The t%! f!rms !f #!cat!rs use f!r interna# #!cati!n are #!cating pins an #!cating p#ugs$ The !n#y ifference

"et%een these #!cat!rs is their si0e1 #!cating pins are use f!r sma##er h!#es an #!cating p#ugs are use f!r #arger

h!#es$

)s sh!%n in 5igure =&F, the p#ate uner the %!r(piece restricts !ne egree !f free!m$ It prevents any a/ia

m!vement !%n%ar, a#!ng the &0 ?@ a/is$ The center pin, acting in c!n3uncti!n %ith the p#ate as a c!ncentric

#!cat!r, prevents any a/ia# !r raia# m!vement a#!ng !r a"!ut the / ?8, 9, F, an M@ an y ?=, >, , an 8J@

a/es$ T!gether, these t%! #!cat!rs restrict nine egrees !f free!m$ The fina# #!cat!r, the pin in the !uter h!#e, is

the raia# #!cat!r that restricts t%! egrees !f free!m "y arresting the raia# m!vement ar!un the 0 ?88 an

89@ a/is$ T!gether, the #!cat!rs restrict e#even egrees !f free!m$ The #ast egree !f free!m, in the 0

irecti!n, %i## "e restricte %ith a c#amp$

5igure =&F$ T%! #!cating pins m!unte !n a p#ate restrict e#even&!ut&!f&t%e#ve egrees !f free!m$

)na#y0ing -achining 5!rces

The m!st&imp!rtant fact!rs t! c!nsier in fi/ture #ay!ut are the irecti!n an magnitue !f machining f!rces

e/erte uring the !perati!n$ In 5igure =&M, the mi##ing f!rces generate !n a %!r(piece %hen pr!per#y c#ampe in

a vise ten t! push the %!r(piece !%n an t!%ar the s!#i 3a%$ The c#amping acti!n !f the m!va"#e 3a% h!#s

the %!r(piece against the s!#i 3a% an maintains the p!siti!n !f the part uring the cut$

5igure =&M$ Cutting f!rces in a mi##ing !perati!n sh!u# "e irecte int! the s!#i 3a% an "ase !f the vise$

)n!ther e/amp#e !f cutting f!rces !n a %!r(piece can "e seen in the ri##ing !perati!n in 5igure =&$ The

primary machining f!rces ten t! push the %!r(piece !%n !nt! the %!r(h!#er supp!rts$ )n aiti!na

machining f!rce acting raia##y ar!un the ri## a/is a#s! f!rces the %!r(piece int! the #!cat!rs$ The c#amps that


23/36


24/36

LOC)TING GUIDLIN*

N! sing#e f!rm !f #!cati!n !r type !f #!cat!r %i## %!r( f!r every %!r(h!#er$ T! pr!per#y perf!rm the

necessary #!cati!n, each #!cat!r must "e carefu##y p#anne int! the esign$ The f!##!%ing are a fe% guie#ines t!

!"serve in ch!!sing an app#ying #!cat!rs$

;!siti!ning L!cat!rs

The primary functi!n !f any #!cat!r is t! reference the %!r(piece an t! ensure repeata"i#ity$ Un#ess the

#!cat!rs are pr!per#y p!siti!ne, h!%ever, these functi!ns cann!t "e acc!mp#ishe$ When p!siti!ning #!cat!rs

"!th re#ative t! the %!r(h!#er an t! the %!r(piece, there are a fe% "asic p!ints t! (eep in min$

Whenever practica#, p!siti!n the #!cat!rs s! they c!ntact the %!r(piece !n a machine surface$ The

machine surface n!t !n#y pr!vies repeata"i#ity "ut usua##y !ffers a m!re&sta"#e f!rm !f #!cati!n$ The %!r(piece

itse#f etermines the areas !f the machine surface use f!r #!cati!n$ In s!me instances, the entire surface may

"e machine$ In !thers, especia##y %ith castings, !n#y se#ecte areas are machine$

The "est machine surfaces t! use f!r #!cati!n, %hen avai#a"#e, are machine h!#es$ )s previ!us#y n!te

machine h!#es !ffer the m!st&c!mp#ete #!cati!n %ith a minima# num"er !f #!cat!rs$ The ne/t c!nfigurati!n that

aff!rs ae.uate repeata"i#ity is t%! machine surfaces f!rming a right ang#e$ These characteristics are %e#

suite f!r the si/&p!int #!cati!na# meth!$ Regar#ess !f the type !r c!niti!n !f the surfaces use f!r #!cati!n

h!%ever, the primary re.uirement in the se#ecti!n !f a #!cating surface is repeata"i#ity$

T! ensure repeata"i#ity, the ne/t c!nsierati!n in the p!siti!ning !f #!cat!rs is the spacing !f the #!cat!rs

themse#ves$ )s a ru#e, space #!cat!rs as far apart as practica#$ This is i##ustrate in 5igure =&89$ 2!th %!r(pieces

sh!%n here are #!cate %ith the si/&p!int #!cating meth!$ The !n#y ifference #ies in the spacing !f the #!cat!rs$

In the part sh!%n at ?"@, "!th #!cat!rs !n the "ac( sie are p!siti!ne c#!se t! each !ther$ In the part at ?a@, these

same #!cat!rs are space further apart$ The part at ?a@ is pr!per#y #!cate7 the part at ?"@ is n!t$ *pacing the

#!cat!rs as far apart as practica# c!mpensates f!r irregu#arities in either the #!cat!rs !r the %!r(piece$ Its a#s!

aff!rs ma/imum sta"i#ity$

5igure =&89$ L!cat!rs sh!u# "e space as far apart as practica# t! c!mpensate f!r s#ight irregu#arities an f!r ma/imum sta"i#ity$

The e/amp#es in 5igure =&8= sh!% c!niti!ns that may !ccur %hen #!cat!rs are p#ace t!! c#!se t!gether if

the center p!siti!ns !f the #!cat!rs are misa#igne "y $JJ86$ With the spacing sh!%n at ?a@, this c!niti!n has #itt#e

effect !n the #!cati!n$ 2ut if the #!cating an spacing %ere change t! that sh!%n at ?"@, the $JJ86 ifference

%!u# have a su"stantia# effect$ )n!ther pr!"#em %ith #!cat!rs p#ace t!! c#!se t!gether is sh!%n at ?c@$ Here,

"ecause the #!cat!rs are t!! c#!se#y space, the part can %!""#e a"!ut the #!cat!rs in the %!r(h!#er$


25/36

5igure =&8=$ ;!siti!ning #!cat!rs t!! c#!se t!gether %i## affect the #!cati!na# accuracy$

C!ntr!##ing Chips

The fina# c!nsierati!n in the p#acement !f #!cat!rs inv!#ves the pr!"#em !f chip c!ntr!#$ Chips are an

inevita"#e part !f any machining !perati!n an must "e c!ntr!##e s! they ! n!t interfere %ith #!cating the

%!r(piece in the %!r(h!#er$ *evera# meth!s he#p minimi0e the chip pr!"#em$ 5irst, p!siti!n the #!cat!rs a%ay

fr!m areas %ith a high c!ncentrati!n !f chips$ If this is n!t practica#, then re#ieve the #!cat!rs t! reuce the effect

!f chips !n the #!cati!n$ In either case, t! minimi0e the negative effects !f chips, use #!cat!rs that are easy t!

c#ean, se#f&c#eaning, !r pr!tecte fr!m the chips$ 5igure =&8> sh!%s severa# %ays that #!cat!rs can "e re#ieve t!

reuce chip pr!"#ems$

5igure =&8>$ L!cat!rs sh!u# "e re#ieve t! reuce #!cati!na# pr!"#ems cause "y chips$

C!!#ant "ui#&up can a#s! cause pr!"#ems$ *!#ve this pr!"#em "y ri##ing h!#es, !r mi##ing s#!ts, in areas !f

the %!r(h!#er %here the c!!#ant is m!st #i(e#y t! "ui# up$ With s!me %!r(h!#ers, c!!#ant&rain areas can a#s!

act as a rem!va# p!int f!r accumu#ate chips$

When esigning a %!r(h!#er, a#%ays try t! minimi0e the chip pr!"#em "y rem!ving areas !f the t!!# %here

chips can "ui# up$ Omit areas such as insie c!rners, unre#ieve pins, !r simi#ar features fr!m the esign$ Chip

c!ntr!# must "e aresse in the esign !f any 3ig !r fi/ture$


26/36

)v!iing Reunant L!cati!n

)n!ther c!niti!n t! av!i in %!r(h!#er esign is reunant, !r up#icate, #!cati!n$ Reunant #!cat!rs

restrict the same egree !f free!m m!re than !nce$ The %!r(pieces in 5igure =&8A sh!% severa# e/amp#es$ The

part at ?a@ sh!%s h!% a f#at surface can "e reunant#y #!cate$ The part sh!u# "e #!cate !n !n#y !ne, n!t "!th

sie surfaces$ *ince the si0es !f parts can vary, %ithin their t!#erances, the #i(e#ih!! !f a## parts resting

simu#tane!us#y !n "!th surfaces is rem!te$ The e/amp#e at ?"@ p!ints !ut the same pr!"#em %ith c!ncentric

iameters$ ither iameter can #!cate the part, "ut n!t "!th$

The e/amp#e at ?c@ sh!%s the ifficu#ty %ith c!m"ining h!#e an surface #!cati!n$ ither #!cati!na# meth!,#!cating fr!m the h!#es !r #!cating fr!m the eges, %!r(s %e## if use a#!ne$ When the meth!s are use t!gether,

h!%ever, they cause a up#icate c!niti!n$ The c!niti!n may resu#t in parts that cann!t "e #!ae !r un#!ae as

intene$

5igure =&8A$ /amp#es !f reunant #!cati!n$

)#%ays av!i reunant #!cati!n$ The simp#est %ay t! e#iminate it is t! chec( the sh!p print t! fin %hich

%!r(piece feature is the reference feature$ Often, the %ay a part is imensi!ne inicates %hich surfaces !r

features are imp!rtant$ )s sh!%n in 5igure =&8, since the part !n the #eft is imensi!ne in "!th irecti!ns fr!m

the unersie !f the f#ange, use this surface t! p!siti!n the part$ The part sh!%n t! the right, h!%ever, is

imensi!ne fr!m the "!tt!m !f the sma## iameter$ This is the surface that sh!u# "e use t! #!cate the part$

5igure =&8$ The "est #!cating surfaces are !ften etermine "y the %ay that the part is imensi!ne$


27/36

;reventing Impr!per L!aing

5!!#pr!!fing prevents impr!per #!aing !f a %!r(piece$ The pr!"#em is m!st preva#ent %ith parts that are

symmetrica# !r #!cate c!ncentrica##y$ The simp#est %ay t! f!!#pr!!f a %!r(h!#er is t! p!siti!n !ne !r t%! pins in

a #!cati!n that ensures c!rrect !rientati!n, 5igure =&8F$ With s!me %!r(pieces, h!%ever, m!re&creative

appr!aches t! f!!#pr!!fing must "e ta(en$

5igure =&8F$ 5!!#pr!!fing the #!cati!n prevents impr!per %!r(piece #!aing$

5igure =&8M sh!%s %ays t! f!!#pr!!f part #!cati!n$ In the first e/amp#e, sh!%n at ?a@, an !ther%ise&

n!nfuncti!na# f!!#pr!!fing pin ensures pr!per !rientati!n$ This pin %!u# interfere %ith !ne !f the ta"s if the part

%ere #!ae any !ther %ay$ In the ne/t e/amp#e, sh!%n at ?"@, a cavity in the %!r(piece prevents the part fr!m

"eing #!ae upsie&!%n$ Here, a "#!c( that is s#ight#y sma##er than the !pening !f the part cavity is ae t! the

%!r(h!#er$ ) pr!per#y #!ae part fits !ver the "#!c(, "ut the "#!c( (eeps an impr!per#y #!ae part fr!m

entering the %!r(h!#er$

5igure =&8M$ *imp#e pins !r "#!c(s are !ften use t! f!!#pr!!f the #!cati!n$

Using *pring&L!ae L!cat!rs

One meth! t! he#p ensure accurate #!cati!n is the insta##ati!n !f spring!ae "utt!ns !r pins in the

%!r(h!#er, 5igure =&8$ These evices are p!siti!ne s! their spring f!rce pushes the %!r(piece against the

fi/e #!cat!rs unti# the %!r(piece is c#ampe$ These spring!ae access!ries n!t !n#y ensure repeata"#e

#!cating "ut a#s! ma(e c#amping the %!r(piece easier$


28/36


29/36

5igure =&98$ Determining the si0e !f a sing#e #!cating pin "ase !n ma/imum&materia# c!niti!ns$

The genera# accuracy !f the %!r(h!#er must "e greater than the accuracy !f the %!r(piece$ T%! "asic types

!f t!#erance va#ues are app#ie t! a #!cat!r1 the first are the t!#erances that c!ntr!# the si0e !f the #!cat!r7 the

sec!n are t!#erances that c!ntr!# its #!cati!n$ -any meth!s can "e use t! etermine the appr!priate t!#erance

va#ues assigne t! a %!r(h!#er$ In s!me situati!ns the t!#erance esignati!n is an ar"itrary va#ue preetermine

"y the engineering epartment an assigne t! a %!r(h!#er %ith!ut regar t! the specific %!r(piece$ Other

t!#erances are assigne a specific va#ue "ase !n the si0e !f the e#ement t! "e #!cate$ )#th!ugh m!re

appr!priate than the sing#e&va#ue t!#erances, they ! n!t a##!% f!r re.uirements !f the %!r(piece$ )n!ther

c!mm!n meth! is using a set percentage !f the %!r(piece t!#erance$

The c#!ser the t!#erance va#ue, the higher the !vera## c!st t! pr!uce the %!r(piece$ Genera##y, %hen a

t!#erance is tightene, the c!st !f the t!#erance increases e/p!nentia##y t! its "enefit$ ) t!#erance t%ice as tight

might actua##y c!st five times as much t! pr!uce$

The manufactura"i#ity !f a t!#erance, the a"i#ity !f the avai#a"#e manufacturing meth!s t! achieve a

t!#erance, is a#s! a critica# fact!r$ ) simp#e h!#e, f!r e/amp#e, if t!#erance t! P$JAJ6, can "e punche$ If, h!%ever,

the t!#erance is P$J8J6, the h!#e re.uires ri##ing$ Li(e%ise, if the t!#erance is tightene t! P$JJ96, the h!#e then

re.uires ri##ing an reaming$ 5ina##y, %ith a t!#erance !f P$JJJ=6, the h!#e must "e ri##e, reame, an #appe t!

ensure the re.uire si0e$

One !ther fact!r t! c!nsier in the manufactura"i#ity !f a t!#erance is %hether the t!#erance specifie can "e

manufacture %ithin the capa"i#ity !f the t!!#r!!m$ ) t!#erance !f $JJJJ86 is very easy t! inicate !n a ra%ing,

"ut is imp!ssi"#e t! achieve in the vast ma3!rity !f t!!#r!!ms$

N! sing#e t!#erance is appr!priate f!r every part feature$ ven th!ugh !ne feature may re.uire a t!#erance !f

#!cati!n t! %ithin $JJJA6, it is !u"tfu# that every t!#erance !f the %!r(h!#er must "e he# t! the same t!#erance

va#ue$ The #ength !f a "asep#ate, f!r e/amp#e, can usua##y "e mae t! a su"stantia##y ifferent t!#erance than the

#!cati!n !f the specific features$

The app#icati!n !f percentage&type t!#erances, un#i(e ar"itrary t!#erances, can accurate#y ref#ect the

re#ati!nship "et%een the %!r(piece t!#erances an the %!r(h!#er t!#erances$ *pecificati!n !f %!r(h!#er

t!#erances as a percentage !f the %!r(piece t!#erances resu#ts in a c!nsistent an c!nstant re#ati!nship "et%een

the %!r(h!#er an the %!r(piece$ When a straight percentage va#ue !f 9A percent is app#ie t! a $JAJ6 %!r(piece

t!#erance, the %!r(h!#er t!#erance is $J89A6$ The same percentage app#ie t! a $JJ86 t!#erance is $JJJ9A6$ Here a

pr!p!rti!na# re#ati!nship !f the t!#erances is maintaine regar#ess !f the re#ative si0es !f the %!r(piece

t!#erances$ )s a ru#e, the range !f percentage t!#erances sh!u# "e fr!m 9J t! AJ percent !f the %!r(piece

t!#erance, usua##y etermine "y engineering&epartment stanars$


30/36

CL)-;ING GUIDLIN*

L!cating the %!r(piece is the first "asic functi!n !f a 3ig !r fi/ture$ Once #!cate, the %!r(piece must a#s! "e

he# t! prevent m!vement uring the !perati!na# cyc#e$ The pr!cess !f h!#ing the p!siti!n !f the %!r(piece in

the 3ig !r fi/ture is ca##e c#amping$ The primary evices use f!r h!#ing a %!r(piece are c#amps$ T! perf!rm

pr!per#y, "!th the c#amping evices an their #!cati!n !n the %!r(h!#er must "e carefu##y se#ecte$

5act!rs in *e#ecting C#amps

C#amps serve t%! primary functi!ns$ 5irst, they must h!# the %!r(piece against its #!cat!rs$ *ec!n, the

c#amps must prevent m!vement !f the %!r(piece$ The #!cat!rs, n!t the c#amps, sh!u# resist the primary cutting

f!rces generate "y the !perati!n$

%olding the &or'pie"e #gainst Lo"ators.C#amps are n!t intene t! resist the primary cutting f!rces$ The

!n#y purp!se !f c#amps is t! maintain the p!siti!n !f the %!r(piece against the #!cat!rs an resist the sec!nary

cutting f!rces$ The sec!nary cutting f!rces are th!se generate as the cutter #eaves the %!r(piece$ In ri##ing, f!r

e/amp#e, the primary cutting f!rces are usua##y irecte !%n an raia##y a"!ut the a/is !f the ri##$ The

sec!nary f!rces are the f!rces that ten t! #ift the part as the ri## "rea(s thr!ugh the !pp!site sie !f the part$

*!, the c#amps se#ecte f!r an app#icati!n nee !n#y "e str!ng en!ugh t! h!# the %!r(piece against the #!cat!rs

an resist the sec!nary cutting f!rces$

The re#ati!nship "et%een the #!cat!rs an c#amps can "e i##ustrate %ith a mi##ing&machine vise$ In 5igure =&99, the vise c!ntains "!th #!cating an c#amping e#ements$ The s!#i 3a% an vise "!y are the #!cat!rs$ The

m!va"#e 3a% is the c#amp$ The vise is n!rma##y p!siti!ne s! that the #!cat!rs resist the cutting f!rces$ Directing

the cutting f!rces int! the s!#i 3a% an vise "!y ensures the accuracy !f the machining !perati!n an prevents

%!r(piece m!vement$ In a## %!r(h!#ers, it is imp!rtant t! irect the cutting f!rces int! the #!cat!rs$ The m!va"#e

vise 3a%, #i(e !ther c#amps, simp#y h!#s the p!siti!n !f the %!r(piece against the #!cat!rs$

5igure =&99$ ) vise c!ntains "!th #!cating an c#amping e#ements$

%olding Se"urely Under (i$ration) Loading) and Stress. The ne/t fact!rs in se#ecting a c#amp are the

vi"rati!n an stress e/pecte in the !perati!n$ Cam c#amps, f!r e/amp#e, a#th!ugh g!! f!r s!me !perati!ns, are

n!t the "est ch!ice %hen e/cessive vi"rati!n can #!!sen them$ It is a#s! a g!! iea t! a a safety margin t! the

estimate f!rces acting !n a c#amp$

Preventing *amage to the &or'pie"e. The c#amp ch!sen must a#s! "e !ne that !es n!t amage the

%!r(piece$ Damage !ccurs in many %ays$ The main c!ncerns are part ist!rti!n an marring$ T!! much c#amping

f!rce can %arp !r "en the %!r(piece$ *urface amage is !ften cause "y c#amps %ith harene !r n!n&r!tating

c!ntact surfaces$ Use c#amps %ith r!tating c!ntact pas !r %ith s!fter c!ntact materia# t! reuce this pr!"#em

The "est c#amp f!r an app#icati!n is !ne that can ae.uate#y h!# the %!r(piece %ith!ut surface amage$

Improving Load+Unload Speed.The spee !f the c#amps is a#s! imp!rtant t! the %!r(h!#er's efficiency$ )

c#amp %ith a s#!% c#amping acti!n, such as a scre% c#amp, s!metimes e#iminates any pr!fit p!tentia# !f the

%!r(h!#er$ The spee !f c#amping an unc#amping is usua##y the m!st&imp!rtant fact!r in (eeping

#!aing


31/36

;!siti!ning the C#amps

The p!siti!n !f c#amps !n the %!r(h!#er is 3ust as imp!rtant t! the !vera## !perati!n !f the t!!# as the

p!siti!n !f the #!cat!rs$ The se#ecte c#amps must h!# the part against the #!cat!rs %ith!ut ef!rming the

%!r(piece$ Once again, since the purp!se !f #!cat!rs is t! resist a## primary cutting f!rces generate in the

!perati!n, the c#amps nee !n#y "e #arge en!ugh t! h!# the %!r(piece against the #!cat!rs an t! resist any

sec!nary f!rces generate in the !perati!n$ T! meet "!th these c!niti!ns, p!siti!n the c#amps at the m!st&rigi

p!ints !f the %!r(piece$ With m!st %!r(h!#ers, this means p!siti!ning the c#amps irect#y !ver the supp!rting

e#ements in the "asep#ate !f the %!r(h!#er, 5igure&=&9=a$

In s!me cases the %!r(piece must "e c#ampe against h!ri0!nta# #!cat!rs rather than the supp!rts, 5igure =&

9="$ In either case, the c#amping f!rce must "e a"s!r"e "y the #!cating e#ements$

5igure =&9=$ C#amps sh!u# a#%ays "e p!siti!ne s! the c#amping f!rce is irecte int! the supp!rts !r #!cat!rs$

5!r %!r(h!#ers %ith t%! supp!rts uner the c#amping area !f the %!r(piece, t%! c#amps sh!u# "e use

!ne !ver each supp!rt, 5igure =&9>a$ ;#acing !n#y !ne c#amp "et%een the supp!rts can easi#y "en !r ist!rt the

%!r(piece uring the c#amping !perati!n$ When the %!r(piece has f#anges !r !ther e/tensi!ns use f!r c#amping

an au/i#iary supp!rt sh!u# "e p!siti!ne uner the e/tene area "ef!re a c#amp is app#ie, 5igure =&9>"$

5igure =&9>$ The num"er an p!siti!n !f c#amps is etermine "y the %!r(piece an its supp!rts$

)n!ther c!nsierati!n in p!siti!ning c#amps is the !perati!n !f the machine t!!# thr!ugh!ut the machining

cyc#e$ The c#amps must "e p!siti!ne s! they ! n!t interfere %ith the !perati!n !f the machine t!!#, uring either

the cutting !r return cyc#e$ *uch p!siti!ning is especia##y critica# %ith numerica##y c!ntr!##e machines$ In aiti!n

t! the cutters, chec( interference "et%een the c#amps an !ther machine e#ements, such as ar"!rs, chuc(s, .ui##s

#athe carriages, an c!#umns$

When fi/turing an aut!mate machine, chec( the c!mp#ete t!!# path "ef!re using the %!r(h!#er$ Chec(

"!th the machining cyc#e an return cyc#e !f the machine f!r interference "et%een the cutters an the c#amps

Occasi!na##y pr!grammers f!rget t! c!nsier the t!!# path !n the return cyc#e$ One %ay t! reuce the chance !f a

c!##isi!n an e#iminate the nee t! pr!gram the return path is simp#y t! raise the cutter a"!ve the highest area !f

the %!r(piece !r %!r(h!#er at the en !f the machining cyc#e "ef!re returning t! the h!me p!siti!n$


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-!st c#amps are p!siti!ne !n !r near the t!p surface !f the %!r(piece$ The !vera## height !f the c#amp, %ith

respect t! the %!r(piece, must "e (ept t! a minimum$ This can "e !ne %ith g!!senec(&type c#amps, 5igure =&9A

)s sh!%n, the g!!senec( c#amp has a #!%er pr!fi#e an sh!u# "e use %here reuce c#amp height is neee$

5igure =&9A$ Using g!!senec( c#amps is !ne %ay t! reuce the height !f the c#amps$

The si0e !f the c#amp&c!ntact area is an!ther fact!r in p!siti!ning a c#amp$ T! reuce interference "et%een

the c#amp an the cutter, (eep the c!ntact area as sma## as safe#y p!ssi"#e$ ) sma## c#amping area reuces thechance f!r interference an a#s! increases the c#amping pressure !n the %!r(piece$ The !vera## si0e !f the c#amp

is an!ther fact!r t! (eep in min$ The c#amp must "e #arge en!ugh t! pr!per#y an safe#y h!# the %!r(piece, "ut

sma## en!ugh t! stay !ut !f the %ay$

Once again, the primary purp!se !f a c#amp is t! h!# the %!r(piece against the #!cat!rs$ T! ! this

pr!per#y, the c#amping f!rce sh!u# "e irecte int! the #!cat!rs, !r the m!st&s!#i part !f the %!r(h!#er

;!siti!ning the c#amping evices in any !ther manner can easi#y ist!rt !r ef!rm the %!r(piece$

The %!r(piece sh!%n in 5igure =&9 i##ustrates this p!int$ The part is a thin&%a## ring that must "e fi/ture s!

that the interna# iameter can "e "!re$ The m!st&c!nvenient %ay t! c#amp the %!r(piece is !n its !utsie

iameter7 h!%ever, t! generate en!ugh c#amping pressure t! h!# the part, the c#amp is #i(e#y t! ef!rm the ring

The reas!n #ies in the irecti!n an magnitue !f the c#amping f!rce1 rather than acting against a #!cat!r, the

c#amping f!rces act against the spring f!rce !f the ring resisting the c#amping acti!n$ This type !f c#amping

sh!u# !n#y "e use if the part is a s!#i is( !r has a sma##&iameter h!#e an a heavy %a## thic(ness$

5igure =&9$ Directing the c#amping f!rces against an unsupp!rte area %i## cause this cy#inrica# part t! ef!rm$

T! c#amp this type !f part, !ther techni.ues sh!u# "e use$ The c#amping arrangement in 5igure =&9F sh!%s

the %!r(piece c#ampe %ith f!ur strap c#amps$ The c#amping f!rce is irecte int! the "asep#ate an n!t against


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5igure =&9$ When the part can !n#y "e c#ampe !n its !utsie surface, pie&shape chuc( 3a%s can "e use t! h!# the part an reuceef!rmati!n$

*e#ecting C#amp *i0e an 5!rce

Ca#cu#ati!ns t! fin the necessary c#amping f!rce can "e .uite c!mp#icate$ In many situati!ns, h!%ever, an

appr!/imate eterminati!n !f these va#ues is sufficient$ The ta"#e in 5igure =&=J sh!%s the avai#a"#e c#amping

f!rces f!r a variety !f ifferent&si0e manua# c#amp straps %ith a 9&t!&8 c#amping&f!rce rati!$

5igure =&=J$ )ppr!/imate c#amping f!rces !f ifferent&si0e manua# c#amp straps %ith a 9&t!&8 c#amping&f!rce rati!$

)#ternative#y, re.uire c#amping f!rce can "e ca#cu#ate "ase !n ca#cu#ate cutting f!rces$ ) simp#ifie

e/amp#e is sh!%n in 5igure =&=8$ The cutting f!rce is entire#y h!ri0!nta#, an n! %!r(piece #!cat!rs are use, s!

fricti!na# f!rces a#!ne resist the cutting f!rces$


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5igure =&=8$ ) simp#ifie c#amping&f!rce ca#cu#ati!n %ith the cutting f!rce entire#y h!ri0!nta#, an n! %!r(piece st!ps ?fricti!na# f!rceresists a## cutting f!rces@$

When %!r(piece #!cat!rs an mu#ti&irecti!na# f!rces are c!nsiere, the ca#cu#ati!ns "ec!me m!re

c!mp#icate$ T! simp#ify ca#cu#ati!ns, the %!rst&case f!rce situati!n can "e estimate intuitive#y an then treate

as a t%!&imensi!na# static&mechanics pr!"#em ?using a free&"!y iagram@$ In the e/amp#e sh!%n in 5igure =&=9

the cutting f!rce is (n!%n t! "e 8MJJ #"s, "ase !n a previ!us ca#cu#ati!n$ The %!r(piece %eighs 8AJJ #"s$ The

un(n!%n f!rces are1

5R Q T!ta# f!rce fr!m a## c#amps !n right sie

5L Q T!ta# f!rce fr!m a## c#amps !n #eft sie

R8 Q H!ri0!nta# reacti!n f!rce fr!m the fi/e st!p

R9 Q Bertica# reacti!n f!rce fr!m the fi/e st!p

R= Q Bertica# reacti!n f!rce !n the right sie

N Q N!rma#&irecti!n f!rce Q 5L 5R 8AJJ

Q C!efficient !f fricti!n Q $8

5igure =&=9$ ) m!re&c!mp#icate c#amping&f!rce ca#cu#ati!n, using a t%!&imensi!na# free&"!y iagram$

The f!##!%ing e.uati!ns s!#ve the un(n!%n f!rces assuming that f!r a static c!niti!n1


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8$ The sum !f f!rces in the / irecti!n must e.ua# 0er!$

9$ The sum !f f!rces in the y irecti!n must e.ua# 0er!$

=$ The sum !f m!ments a"!ut any p!int must e.ua# 0er!$

)t first g#ance, this e/amp#e #!!(s 6statica##y ineterminate,6 i$e$, there are five varia"#es an !n#y three

e.uati!ns$ 2ut f!r the minimum re.uire c#amping f!rce, R =is 0er! ?%!r(piece "are#y t!uching@ an 5 L is 0er!

?there is n! tenency t! #ift !n the #eft sie@$ N!% %ith !n#y three varia"#es, the pr!"#em can "e s!#ve1

*!#ving f!r the varia"#es,

5RQ 89J #"s

R8Q 89FJ #"s

R9Q 9FJ #"s

In !ther %!rs, the c!m"ine f!rce fr!m a## c#amps !n the right sie must "e greater than 89J #"s$ With a

rec!mmene safety fact!r !f 9&t!&8, this va#ue "ec!mes 9AMJ #"s$ ven th!ugh 5 L?c!m"ine f!rce fr!m a## thec#amps !n the #eft sie@ e.ua#s 0er!, a sma## c#amping f!rce may "e esira"#e t! prevent vi"rati!n$

)n!ther genera# area !f c!ncern is maintaining c!nsistent c#amping f!rce$ -anua# c#amping evices can vary

in the f!rce they app#y t! parts uring a pr!ucti!n run$ -any fact!rs acc!unt f!r the variati!n, inc#uing c#amp

p!siti!n !n the %!r(piece, "ut !perat!r fatigue is the m!st&c!mm!n fau#t$ The simp#est an !ften&"est %ay t!

c!ntr!# c#amping f!rce is t! rep#ace manua# c#amps %ith p!%er c#amps$

The f!rce generate "y p!%er c#amps is n!t !n#y c!nstant "ut a#s! a3usta"#e t! suit %!r(piece c!niti!ns$

)n!ther "enefit !f p!%er c#amps is their spee !f !perati!n1 n!t !n#y are iniviua# p!%er c#amps faster than

manua# c#amps, every c#amp is activate at the same time$

Documents

CarrLane Jig Fixture