Download - Lathe Part I

7/25/2019 Lathe Part I

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OVERVIEW

Lathe Principle of working, specification of lathe types of lathe

Lathe operations & Important Accessories aper t!rning & threa"

t!rning#Pro$lems#machining time calc!lations%

!rret an" apstan lathes 'ifferences tool hol"ing "e(ices # tool

layo!t, e)amples%

*haping an" Planing machines 'ifferences# Principles of working

+!ick ret!rn mechanisms# Principal parts specification, classification,

operations performe", machining time calc!lations%

UNIT II


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The Lathe Machine Tool


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Invented by the English Inventor

Henry Maudsley in 1757


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Li(e center


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Princile o! "or#ing o! Lathe

A achine tool which remo(es the metal from a piece of ro!n"-cylin"rical. work to the re/!ire" shape & si0e $y hol"ing the work

$etween two rigi" an" strong s!pports calle" centers or in a ch!ck or

face plate while the work re(ol(es% he c!tting tool is rigi"ly hel" an"

s!pporte" in a tool post an" is fe" against the re(ol(ing work%


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$riving Plate and Lathe %arriers &r $ogs

Li(e

'ea"


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ARRIA1E

AI2 PAR*


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AI2 PAR*

HE'$ (T&%)# his en" of the lathe contains the "ri(ing motor an"

gears% Power to rotate the part is "eli(ere" from here% his typically has

le(ers that let the spee"s an" fee"s $e set%

T'IL (T&%)# his can $e !se" to hol" the other en" of the part or perform

"rilling, reaming, $oring etc%, operations on work%

L'THE *E$ +',(# hese are har"ene" rails that the carriage an" tailstock

ri"es on%

L'THE *E$ 3ase on which "ifferent fi)e" an" operating parts of the lathe

are mo!nte"%

%'--I'.E# his part of the lathe carries the c!tting tool an" mo(es

$ase" on the rotation of the lea" screw or fee" ro"%

/EE$ -&$ # A long shaft !se" for "ri(ing carriage for (ario!s c!tting fee"s%

LE'$ (%-E+# A large screw with a few threa"s per inch !se" for

c!tting threa"s


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Tyes

o!

Lathe

Engine Lathe

*ench Lathe

(eed Lathe

Tool -oo0

Lathe

%astan Turret

Lathes

'uto0atic Lathe

(ecial uroseLathes

he most common form of lathe, motor

"ri(en an" comes in large (ariety of si0es

an" shapes 1eneral p!rpose

4or small & precision work# mo!nte"

on $ench

Employe" for woo" t!rning, metal

spinning etc%,#tool fe" & act!ate" $y

han"#no carriage, no gear $o)

*i0e same as engine lathe#for more

acc!rate & precision work# has all

attachments

4or high pro"!ction rates#semi#

a!tomatic type#less operator skill

4or mass pro"!ction#no operator

inter(ention

rankshaft lathe, screw c!tting

lathe, tracer lathe, facing lathe


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EN.INE L'THE

HE'$ (T&%)

T'IL (T&%)

L'THE *E$

%'--I'.E /EE$ -&$

LE'$ (%-E+


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E21I2E LA5E


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*ench Lathe


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(eed Lathe


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Tool -oo0 Lathe


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%astan Turret Lathes


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67

89

66 :

;

6% Range of spin"le spee"s

67% etric threa"s@ Pitch range

66% Inch hrea"s@ Pitch range

6


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Lathe &erations

Turning3opro"!ce *traight, apere", c!r(e", or groo(e" workpieces

/acing@ o pro"!ce a flat s!rface at the en" of the part or for making face

groo(es%

Threading3 o pro"!ce e)ternal or internal threa"s

)nurling3 o pro"!ce a reg!larly shape" ro!ghness on cylin"rical

s!rfaces

$rilling3 o pro"!ce a hole $y fi)ing a "rill in the tailstock

*oring3 o enlarge a hole or cylin"rical ca(ity ma"e $y a pre(io!s

process or to pro"!ce circ!lar internal groo(es%


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Lathe &erations


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Lathe &erations


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he 3e" forms the $ase of a Lathe machine%

It pro(i"es a hea(y rigi" frame on which all the other $asic

components are mo!nte"% It m!st $e rigi" eno!gh to resist "eflection inany "irection !n"er loa"%

he $e" is ma"e as single piece casting !sing cast iron, in a $o)

shape incorporating cross ri$s, an" is s!pporte" on legs, a ca$inet, or

a $ench%

ast iron# Easy sli"ing action, wear resistance an" a$sor$s (i$rations%

o a(oi" "istortions "!ring soli"ification of castings, it is allowe" for

ageing with ro!gh machining an" left in open for co!ple of years an"then machine" to the re/!ire" si0e for final assem$ly%

he hea"stock an" the tailstock are locate" at either en" of the $e"

an" the carriage rests o(er the Lathe $e" an" sli"es o(er it%4ine graine" with


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he ways of the lathe are the flat or V#shape" s!rfaces on which

the carriage an" the tailstock are mo(e" left an" right%

Each has its separate pair of ways, often one flat s!rface, for

sta$ility an" s!pports $y taking ma)im!m portion of loa" an"

stresses, an" one V#way for g!i"ance-g!i"eways. in a perfectly

straight line & "isallows the entry of chips an" "!rt $etween the

sa""le an" $e" an" pre(enting the contact s!rfaces from $eing

spoile" "!e to scratching

hese ways are har"ene" an" scrape" or gro!n" to close

tolerances%

he $asic acc!racy of mo(ement of the carriage "epen"s on the

ways%

3e"3e"waysways

o impro(e wear resistance of $e"s@

6%hilling of casting


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L'THE *E$ 'N$ *E$ +',(


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L'THE *E$

L'THE *E$ +',(


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he hea"stock is the powere" en" an" is always at the

operatorBs left%

his contains the spee" changing gears an" the re(ol(ing,

"ri(ing spin"le, to which any one of se(eral types of work

hol"ers is attache"%

he center of the spin"le is hollow so that long $ars may $e p!t

thro!gh it for machining%

A li(e centre, a face plate, collet or a ch!ck can $e fitte" to thespin"le nose to hol" an" "ri(e the work%

5ea"stock spin"le can $e "ri(en $y a steppe" p!lley an" a $elt

or $y transmission gears in the hea"stock%

HE'$ (T&%)


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Head (toc#

*er(es as a ho!sing for the "ri(ing p!lleys an" $ack gears, pro(i"es $earing

4or the machine spin"le an" keeps the spin"le in alignment with the $e"%

6%one p!lley


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* #


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4*ac# gears

hese are !se" for re"!ction in spin"le spee"s, there $y facilitating a wi"er

range of spee"s%

3ack gears are mo!nte" on an eccentric shaft which is operate" $y means

of a han" le(er known as $ackgear engaging le(er%

3ack gears consists of a sp!r gear an" a pinion% When spee" re"!ction is

"esire", the spring kno$ is p!lle" o!t to make the cone p!lly free of gear on

spin"le an" hence free from spin"le%

he $ack gears are p!t into mesh with the spin"le gears $y p!lling the

eccentric shaft%

2ow the se/!ence of transmission of motion an" power is thro!gh the!pper eccentric shaft an" re"!ction in spee" is possi$le


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Witho!t 3ackgears

With 3ackgears


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HE'$ (T&%) .E'- *&6


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HE'$ (T&%) .E'- *&6

1 ranslating 1ear -6


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HE'$ (T&%) .E'- *&6

All geare" hea" stock is the common mechanism !se" in all mo"ern

lathes he mechanism of gear operation is Csli"ing gear mechanismD

he spin"le spee"s are arrange" in a geometric progression

he "ifferent spin"le spee" possi$le are@

-6. 16 18 F 18 1= - -8. 1

A"(antages of gear "ri(e@

6. ore compact "esign


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4 L'THE (PIN$LE 8Main (indle or Head stoc# sindle9

ain spin"le is hollow an" tapere" at front en" to

accommo"ate centers%

A tapere" slee(e -$!sh. fits into the tapere" hole an" a li(e

center which s!pports the work fits into the slee(e

At font en", the o!tsi"e s!rface is threa"e" to accommo"ate

Go$ hol"ing "e(ices like ch!cks, face plate, "ri(ing plate%

he spin"le re(ol(es on two large thr!st $earings ho!se" on

the hea" stock casting%


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L'THE (PIN$LE %ontd44

5ollow shaft# hrea"e" front en" to recei(e the Go$ hol"ing "e(ices s!ch

as ch!ck, face plate or "ri(ing plate%

r!eness of the spin"le has a consi"era$le effect on the acc!racy of the

Go$, an" hence it sho!l" always $e in perfect alignment


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HE'$ (T&%) (PIN$LE


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:4Live %entre

It is the centre s!pport which is fitte" into the tapere" insi"e portion of

the spin"le nose while !sing a "ri(e plate or face plate

2o s!ch centre is re/!ire" when the work is hel" in ch!ck%

It acts as a $earing s!pport for the work "!ring the operation

It is !s!ally softer than the "ea" centre fitte" in the tail stock, as

there is no wear occ!rring on li(e centre s!rface as it is always

re(ol(ing along with the work

5 /eed -everse lever8/eed $irection lever9 using Tu0bler 0echanis0


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54/eed -everse lever8/eed $irection lever9 using Tu0bler 0echanis0

4or pro(i"ing power fee"s to the carriage% Le(er is at hea" stock an" all

gears are in Apron of carriage

? positions of le(er

6%entral position@ 'isengage"carriage is mo(e" $y han" wheel


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4ee" 'irection Le(er-!m$ler 1ear.# 5ea" stock

Power 4ee" Le(er#Apron

!m$ler re(ersing echanism


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he gear mechanism operate" $y means of the fee" re(erse le(er is calle"

the !m$ler re(ersing mechanism%

Hse" for pro(i"ing power fee"s to the carriage%

otion from the spin"le to the lea" screw or fee" ro" is transmitte" thro!gh

this mechanism%

!m$ler re(ersing echanism

A "esire" spee" of lea" screw or fee" ro" can $e o$taine" $y selecting the

s!ita$le change gears ha(ing proper no% of teeth%

*t!" gears an" /!a"rant are !se" to ena$le proper meshing of change

gears%

% i


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he carriage can $e mo(e" left or right either $y han"

wheel or power fee"%

arriage consists of the following parts@

-6. *a""le,-


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%'--I'.E

4ee"


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otions of a arriage


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he sa""le is an 5#shape" casting that fits o(er the $e"

an" sli"es along the $e" ways% It carries the cross#sli"e an" tool post%

14(addle14(addle

he cross sli"e is mo!nte" on the carriage an" can $emo(e" in an" o!t perpen"ic!lar to the carriage motion%

his is the part that mo(es when facingc!ts are ma"e withpower fee"%

his, or the compo!n", is also !se" to set the "epth of c!twhen t!rning%

he cross sli"e can $e mo(e" $y its han" wheel or $ypower fee"%

4%ross (lide4%ross (lide

% d - t % d - t


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he compo!n" rest is fitte" on the top of the cross#sli"e, is !se"to s!pport the c!tting tool%

It can $e swi(ele" to any angle for taper t!rning operations an"is mo(e" man!ally%

It can $e mo(e" in an" o!t $y its han" wheel for facing or forsetting the "epth of c!t%

It can also $e rotate" ?97 "egrees an" fe" $y its han" wheel atany angle%

4%o0ound -est34%o0ound -est3

: T&&L P&(T(


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he tool post is mo!nte" on the compo!n" rest%

his can $e any of se(eral (arieties $!t in its simplest form ismerely a slotte" cylin"er, which can $e mo(e", left or right inthe#slot in the compo!n" an" clampe" in place%

It can also $e rotate" so as to present the c!tter to the workat whate(er angle is $est for the Go$%

he (ario!s types of tool posts are@

6. *ingle screw tool posts


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(a)A tool post for single-point tools and (b) a quick change indexing square

turret, which can hold up to four tools.


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(IN.LE (%-E+ T&&L P&(T(

&PEN (I$E T&&L P&(T


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&PEN (I$E T&&L P&(T

/&U- +', T&&L P&(T


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/&U- +', T&&L P&(T

5 'P-&N;Hanging art in!ront o! the carriage5 'P-&N;Hanging art in!ront o! the carriage


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5ol"s most of the control le(ers thro!gh which power fee"s can$e gi(en to carriage an" the cross#sli"e%

he apron is fastene" to the sa""le, ho!ses the gears an"mechanisms re/!ire" to mo(e the carriage an" cross#sli"ea!tomatically%

he apron han" wheel can $e t!rne" man!ally to mo(e thecarriage along the Lathe $e"% his han" wheel is connecte" toa gear that meshes in a rack fastene" to the Lathe $e"%

It also carries the cl!tch mechanism an" split half n!t%

l!tch mechanism is !se" to transmit motion from the fee" ro"to carriage

*plit half n!t in conG!nction with the lea" screw, mo(es the

whole carriage in threa" c!tting%

54'P-&N;Hanging art in!ront o! the carriage54'P-&N Hanging art in!ront o! the carriage

'P-&N ME%H'NI(M'P-&N ME%H'NI(M


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Apron mechanism is !se" for transferring rotary motion of thefee" ro" an" the lea" screw into fee" motion of the carriage%

3oth a!tomatic longit!"inal an" cross#fee" can $e pro(i"e" tothe carriage $y changing the position of fee" change le(er-power fee" le(er or fee" selection le(er.

he mechanism is so "esigne" that when the half#n!t isengage" with the lea" screw, the a!tomatic fee" motion from thefee" ro" is "isconnecte"%

here is an interlocking "e(ice which pre(ents sim!ltaneo!s

engagement of the carriage with the fee" ro" an" lea" screwan" sa(es the machine from any pro$a$le "amage%

'P-&N ME%H'NI(M'P-&N ME%H'NI(M

Apron mechanism is not capa$le of pro(i"ing power fee"s $oth to

carriage as well as the cross#sli"e sim!ltaneo!sly%

/or hand !eed 3 4ee" *election Le(er is p!t in position


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/or hand !eed 3 4ee" *election Le(er is p!t in position


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4or threa" c!tting, fee" change le(er-power fee" le(er or fee" selection

le(er. on the apron is place" in ne!tral position an" the carriage in "esire"

position can $e clampe" to the $e" $y tightening the carriage lock#screw%

he motion is transmitte" from lea" screw to the carriage $y engaging

the half#n!ts with lea" screw% A threa" "ial is fastene" to the right si"e of

the apron to in"icate the e)act point to engage the half n!ts while c!tting

the threa"s%

A fee" re(erse le(er-in hea" stock. is !se" to control the "irection of

rotation of the lea" screw to c!t left#han" or right#han" threa"s%


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ARRIA1E

/EE$-&$/EE$-&$


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he fee"ro" is a long shaft that has a keyway%

he power is transmitte" from the lathe spin"le to the apron

gears thro!gh a fee"ro" (ia a large n!m$er of gears%

he fee"ro" is !se" to mo(e the carriage or crosssli"e for

t!rning, facing an" all other operations e)cept threa" c!tting%

he lea"screw is powere" $y gears from the hea" stock an" is!se" for pro(i"ing specific acc!rate mechani0e" mo(ement to thecarriage for c!tting threa"s on the workpiece%

he lea"screw has a "efinite pitch% A split n!t is !se" to engage the lea"screw with the carriage%

In some lathes, the lea"screw performs the f!nctions of fee" ro"an" there is no separate fee" ro"%

LE'$(%-E+LE'$(%-E+


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he half n!t makes the carriage to engage or "isengagewith the lea"screw%

It comprises of a pair of half n!ts capa$le of mo(ing in or

o!t of mesh with the lea" screw%

he half n!t can $e engage" with the lea" screw $y

means of a le(er pro(i"e" on the apron%

his mechanism is calle" half n!t mechanism%

he half n!t or split n!t is !se" only for threa" c!tting%

The Hal! Nut or (lit Nut 0echanis0The Hal! Nut or (lit Nut 0echanis0


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(PLIT NUT

ME%H'NI(M

Thread %hasing $ial


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Thread %hasing $ial

T'IL (T&%)


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Also calle" loose hea" stock or p!ppet hea"

Or slee(e

L'THE '%%E((&-IE(


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L'THE '%%E((&-IE(

he "e(ices employe" for Work hol"ingan" ool hol"ing in lathe

are calle" its Accessories

L'THE 'TT'%HMENT(

Attachments are a""itional e/!ipments !se" for specific

p!rposes

E)amples@ aper t!rning attachment, 1rin"ing wheel attachment,

3ar *tops, hrea" chasing "ial, illing attachment%

4or short length, large "iameter wpsh!cksLathe

Accessorie


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+or#

Holding

devices

4or hol"ing wps like pipe el$ows

which cannot $e hel" in ch!ck or

centers

Hse" to "ri(e wp when hel" $etween

centers

4or hol"ing the work $etween centers

4or hol"ing hollow work pieces

o s!pport long slen"er wps when t!rne"

$etween centers

4ace Plate

Angle

Plate

'ri(ing

Plate

Lathe arriers

Or 'ogs

Lathe enters

Lathe an"rels

Rests

Hse" in conG!nction with face plate

Hse" in conG!nction with face plate

Accessorie

s

%HU%)(


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% U% (

4o!r aw

In"epen"ent

ch!ck

hree Gaw

!ni(ersal

ch!ck

om$ination

ch!ck

agnetic

ch!ck

ollet

ch!ck

Air

operate"

ch!ck

Three


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A three Gaw ch!ck is !se" for gripping cylin"rical workpieces

he Gaws ha(e a series of teeth that mesh with spiral groo(es on a circ!lar

plate within the ch!ck%

his plate can $e rotate" $y the key inserte" in the s/!are socket,

res!lting in sim!ltaneo!s ra"ial motion of the Gaws%

*ince the Gaws maintain an e/!al "istance from the ch!ck a)is, cylin"ricalworkpieces are a!tomatically centere" when grippe"%

Also calle" as self centering ch!ck or !ni(ersal ch!ck% All the Gaws mo(e

together in e/!al amo!nts to clamp the work e"!ce

o$ is a!tomatically centre" an" re!"ce the time of set#!p% aws are not

re(ersi$le an" separate internal an" e)ternal Gaws ha(e to $e !se"%

It has less gripping capacity an" centering acc!racy is lost "!e to wear%

his ch!ck is not s!ita$le for irreg!lar shape" workpieces which "eman"s

the !se of fo!r Gaws ch!ck

Three


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Three


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Three


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/our =a" Indeendent chuc#

With the fo!r Gaw ch!ck, each Gaw can $e a"G!ste" in"epen"ently $y

rotation of the ra"ially mo!nte" threa"e" screws%

Altho!gh acc!rate mo!nting of a workpiece can $e time cons!ming,

a fo!r#Gaw ch!ck is often necessary for non#cylin"rical workpieces%


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Magnetic chuc#


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he workpieces are hel" in this ch!ck $y means of powerf!l

electro# magnets%

Hse" for (ery thin wps which cannot $e hel" in ch!ck

g

%ollet %huc#%ollet %huc#


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ollets are !se" when smooth $ar stock, or workpieces that ha(e

$een machine" to a gi(en "iameter, m!st $e hel" more acc!ratelythan normally can $e achie(e" in a reg!lar three or fo!r Gaw ch!ck%

ollets are relati(ely thin t!$!lar steel $!shings that are split into three

longit!"inal segments o(er a$o!t two thir"s of their length%

he smooth internal s!rface of the split en" is shape" to fit the piece

of stock that is to $e hel"%

he e)ternal s!rface at the split en" is a taper that fits within an

internal taper of a collet slee(e place" in the spin"le hole%

When the collet is p!lle" inwar" into the spin"le, $y means of the

"raw $ar that engages threa"s on the inner en" of the collet, the

action of the two mating tapers s/!ee0es the collet segments

together, ca!sing them to grip the workpiece%



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'ir or Hydraulic oerated chuc#


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'ir or Hydraulic oerated chuc#

he workpieces are hel" in this ch!ck $y means of fl!i" press!re

!se" in mass pro"!ction work for fast an" effecti(e gripping

/ace Plate and 'ngle late


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/ace Plate A face plate consists of a circ!lar "isc $ore" o!t an" threa"


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A face plate consists of a circ!lar "isc $ore" o!t an" threa"

to fit the nose of the spin"le% his has ra"ial, plain an" slots for hol"ing work $y $olts

an" clamps% 4ace plates are !se" for hol"ing workpieces which cannot

$e hel" con(eniently hel" $etween centers or ch!cks%


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hi i t i l t h i t f hi " t k

'ngle late


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his is a cast iron plate ha(ing two faces machine" to make

them a$sol!tely at right angles to each other%

5oles an" slots are pro(i"e" on $oth faces so that it may $eclampe" on the face plate an" can hol" the workpiece on the

other face $y clamps an" $olts%

Angle plates are !se" in conG!nction with a face plate whenthe hol"ing s!rface of the workpiece sho!l" $e kept hori0ontal,

as for e)ample, in machining a flange of a pipe el$ow%

When eccentric Go$s are $olte" on the face plate, a $alance

weight or co!nter weight m!st $e a""e"%



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arriers or lathe "ogs an" catch plates are !se" to hol" workpiece

$riving Plate8%atch late9 and Lathe %arriers8$ogs9


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arriers or lathe "ogs an" catch plates are !se" to hol" workpiece

when it is hel" $etween centers% arriers or lathe "ogs are attache" to the en" of the workpiece $y

setscrewsJ catch plates are either screwe" or $olte" to the nose ofhea" stock spin"le% A proGecting pin from the carriers fits into the slots pro(i"e" in the

catch plate

' catch late "ith live centre


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Lathe %enters


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# Re(ol(ing center

-4rictionless center.

4 # Insert type center

A # Or"inary enter E # ippe" enter

1 # Pipe center

3 # 3all enter

Lathe %enters


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' # 5alf center

5 # Hse of 5alf enter


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Lathe Mandrels


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A man"rel is a "e(ice for hol"ing an" rotating hollow

workpiece that has $een pre(io!s "rille" or $ore"%

he work re(ol(es with the man"rel which is mo!nte"

$etween two centers%

It is generally ma"e of high car$on steel%

he en"s are slightly smaller in "iameter an" flattene" to

pro(i"e effecti(e gripping s!rface of the lathe "og

screws%

Lathe Mandrels


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Lathe Mandrels


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-ests


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(teady rest /ollo"er rest


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*tea"y rest4ollower rest



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-ests

(teady rest


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A stea"y rest consists of cast iron $ase, which may $e ma"e

to sli"e on the lathe $e" ways an" clampe" at any "esire"

position where s!pport is necessary% his is so "esigne" that the !pper position is hinge" at one

en" which facilitates setting an" remo(al of the workpiece

witho!t "ist!r$ing the position of the stea"y rest% here are three Gaws on the stea"y rest, two on the lower

$asean" one on the !pper frame, the Gaws may $e a"G!ste"ra"ially $y rotating in"i(i"!al screws to accommo"ate work

of "ifferent "iameters% he main f!nction of the stea"y rest is to pro(i"e s!pport to

a long slen"er work% 4or a (ery long work more than one stea"y rest may $e

!se"% 5owe(er the carriage cannot $e fe" to the f!ll length of the

work when stea"y rest is !se"%

(teady rest

/ollo"er rest3


101/151

A follower rest consists of a CD like casting ha(ing two

a"G!sta$le Gaws which s!pport the work% he rest is $olte" to the $ack en" of the carriage an" mo(es

with it% 3efore setting the follower rest, the en" of the workpiece is

machine" slightly wi"er than the Gaws to pro(i"e the tr!e

$earing s!rface% he tool is slightly in a"(ance position than the Gaws, an" the

tool is fe" longit!"inally $e the carriage, the Gaws always

follow the tool gi(ing contin!o!s s!pport to the workpiece% he follower rest pre(ents the Go$ from springing away when

the c!t is ma"e an" is !se" in finish t!rning operation% he follow rest is normally !se" with small "iameter stock to

pre(ent the workpiece from CspringingD !n"er press!re from

the t!rning tool

/ollo"er rest3

Taer .eo0etry


102/151

$ d

l

'

* % Where, ' K Large "iameter of taper in mm%

" K small "iameter of taper in mm%

l K length of taper part in mm


103/151

E)ample@

If ' K >7mmJ " K ;7mm an" l K 677mm% 4in" the (al!e of M

*ol!tion@ Hsing the relation@

M K >7 ;7 K 667

677

his means the amo!nt of taper is 6@67 -or 667.or in a length of 67 mm the "iameter of the taper is re"!ce" $y 6mm

l

dD

K

Proble03

A shaft of 6


104/151

6.3y a $roa" nose form tool


105/151

his metho" !ses a tool which is a $roa" nose tool ha(ing straight c!tting e"ge%

he tool is set on the work piece at half taper angle, an" is fe" straight into the

work to generate a tapere" angle%

etho" is limite" to t!rn limite" length taper only%

his is "!e to the reason that the metal is remo(e" $y entire c!tting e"ge, an"

any increase in length of the taper will necessitate the !se of a wi"er c!tting e"ge%

his will re/!ire e)cessi(e c!tting press!re, which may "istort the work "!e to

(i$ration an" spoil the work "!e to (i$ration an" spoil the work s!rface%

Work piece

oolfee"

4Taer Turning *y ("iveling the %o0ound -est


106/151

his metho" employs the principle of taper t!rning $y fee"ing the tool

at an angle to the a)is of rotation of the workpiece%

he tool post is on the compo!n" rest an" compo!n" rest is attache"

to a circ!lar $ase, gra"!ate" in "egrees, which may $e swi(ele" an"

clampe" at any "esire" angle -angle limitation # 8:N on either si"e of

lathe a)is%

Once the compo!n" rest is set at the "esire" half taper angle, rotationof the compo!n" sli"e screw $y han" will ca!se the tool to $e fe" at an

angle an" generate the correspon"ing taper%

his metho" is limite" to t!rn a short $!t steep taper owing to limite"

mo(ement of the cross sli"e%

he mo(ement of the tool in this metho" is controlle" $y han", th!s

this gi(es low pro"!ction rate an" poor s!rface capacity%

aper !rning 3y *wi(elling the ompo!n" Rest ont"


107/151

%o0ound rest scre"

aper K -'#".l

l K length of taper, LK otal length $etween centers

Proble03 1


108/151

A Go$ of ;7mm long has to $e taper t!rne" for its f!ll length% he two

res!lting "iameters will $e 87mm an" ?7mm% 4in" the angle tho!gh which

the compo!n" rest sho!l" $e swi(ele" to pro"!ce the "esire" taper%

Pro$lem67

Pro$lem?% alc!late the compo!n" rest angle to t!rn a short taper of 6mm per 6< mm

K @5A

4Taer turning by setting over the tailstoc#


109/151

he principle of t!rning taper $y this metho" is to shift the a)is of

rotation of the workpiece, at an angle to the lathe a)is, an" fee"ing

the tool parallel to the lathe a)is%

he angle at which a)is of rotation of the workpiece is shifte" is

e/!al to half angle of taper%

he amo!nt of seto(er is limite"%

his metho" is s!ita$le for t!rning small taper on long Go$s%

'isa"(antags of this metho"@

6. he li(e an" "ea" centers are not e/!ally stresse" an" the wear is

not !niform%


110/151


111/151

aper !rning 3y *etting O(er he ailstock enter ont"


112/151

' # Large "iameterJ " # *mall "iameterJ L # length of workJ

l # length of taperJ #5alf taper angleJ *#*eto(er

OPVIEW

From geometry:

BC setover


113/151

sin

sin

If the angle , the anle of taper, is very small, for all practical purposes,

sin tan

tan

2

entire length of the work

BC setover

BC AB

setover L

setover L

D dsetover L

l

setover

=

=

=

=

=

=

=

conicity

2

if the taper is turne! on the entire length of the workpiece, then l "

2

D dsetover

=

=

Proble0s3


114/151

6%A Go$ of


115/151

-'#".l K6


116/151

he principle of taper t!rning $y taper t!rning attachment is to

g!i"e the tool in a straight path set at an angle to the a)is of

rotation of the workpiece, while the work is $eing hel" $y ach!ck or $etween centres aligne" to the lathe a)is%

A taper t!rning attachment consists of a frame or $racket which

is attache" to the rear en" of the lathe $e" an" s!pports a g!i"e

$ar pi(ote" at the centre%

he 1!i"e$ar ha(ing gra"!ations in "egrees may $e swi(ele"

on either si"e of the 0ero gra"!ation an" is set at any "esire"

angle with the lathe a)is%

When taper t!rning attachment is !se", the cross sli"e is first

ma"e free from the lea" screw $y remo(ing the $in"er screw%


117/151

6. 3racket or

4rame


118/151


119/151

Taer turning attach0ent

1HI'E 3AR

attach0ent

Thread No0enclatureThread No0enclature


120/151

Thread No0enclatureThread No0enclature


121/151

6. Pitch@ "istance from one point on the threa" to the

correspon"ing point on the a"Gacent threa" meas!re"parallel to threa" a)is


122/151

hrea" sloping left to right from top#Right han" threa"-commonly !se" threa".

hrea" sloping right to left#Left han" threa"

? positions of le(er for !m$ler gear

6%entral position@ 'isengage"carriage is mo(e" $y han" wheel


123/151

(tart o! threads3 his "enote" the no% of separate threa" groo(es r!nning

parallel to each other along the s!rface of the screwe" part% *i l lti t t


124/151

*ingle or m!ltistart

A"(antage of m!ltistart@ o o$tain more a)ial a"(ancement for the same

amo!nt of rotationf the screwe" part as compare" to single start threa"%

*ingle start threa"#lea"Kpitch

'o!$le start threa"#lea"K


125/151

All the threa"s are forme" on the principle of 5eli)

here are two pre#re/!isites for threa" t!rning on lathe@

A specifie" relationship $etween longit!"inal mo(ement of the

c!tting tool an" work rotation m!st esta$lishe"

he c!tting tool sho!l" ha(e an incl!"e" angle correspon"ing to

the threa" angle

3oth Internal & E)ternal threa"s may $e c!t%

4or $oth of these a proper system of gearing $etween the lathe

spin"le an" the lea" screw is re/!ire" so as to esta$lish the re/!ire"

ratio of spee"s $etween the two%

4or lathes e/!ippe" with /!ick change gear $o)o$taining specifie"pitch of threa" is easy # G!st $y operating the gear change le(ers # as

the re/!isite gears are alrea"y mo!nte" spee" an" fee" charts for

partic!lar pitch are a(aila$le on the machine tool

P-IN%IPLE &/ TH-E'$ TU-NIN.


126/151

6 5ea" stock spin"le

< arriage

? Lea" *crew

8 hange gears


127/151

he process of threa" c!tting is to pro"!ce a helical groo(e on a

cylin"rical s!rface $y fee"ing the tool longit!"inally%


128/151

6% he Go$ is re(ol(e" $etween centre or $y a ch!ck% he longit!"inal fee"

sho!l" $e e/!al to the pitch of the threa" to $e c!t per re(ol!tion of the work

piece%


129/151

he principle of threa" c!tting is to pro"!ce a helical groo(e on a

cylin"rical s!rface $y fee"ing the tool longit!"inally

he longit!"inal fee" sho!l" $e e/!al to the pitch of the threa" to $e c!t

per re(ol!tion of workpiece

O$(io!sly there will $e "efinite ratio $etween the longit!"inal fee" of

tool an" spee" of spin"le

he "esire" ratio is o$taine" with the help of lea" screw $y connecting it

to the spin"le thro!gh a train of gears

2ow the motion from the spin"le is transmitte" to the lea" screw

thro!gh these gears

3y engaging the split n!t the mo(ement of the carriage an" hence thetool is g!i"e" $y the lea" screw

If the spin"le spee" an" the lea" screw rotate at the same spee", the

pitch of the threa" c!t on the work will $e the same as that of the lea"

screw

*pin"le spee"#re(ersing gears#change gears#lea" screw#split half

n!t engage"# carriage mo(es# hence the tool


130/151

alc!lating change gears@ o esta$lish a "efinite ratio $etween spin"le

spee" an" longit!"inal tool fee"%

If the spin"le an" lea" screw rotate at the same spee", the pitch of the

threa" c!t on the work will $e the same as that of the lea" screw%

If the pitch of lea" screwK?, the tool will a"(ance parallel to the a)is of thework $y a "istance e/!al to ? mm for each re(ol!tion of the lea" screw,

gi(ing ? mm pitch helical groo(e on the s!rface of the Go$%

If 9 mm pitch is re/!ire" to $e c!t on same lathe, tool sho!l" mo(e a

"istance e/!al to 9 mm for e(ery re(ol!tion of the spin"le%

3!t, since the lea" screw pitch is only ? mm, for 9 mm "isplacement of the

tool, the lea" screw sho!l" make < re(ol!tions% hat is the lea" screw sho!l"

rotate at a spee" "o!$le that of the spin"le%

he spee" of the lea" screw will $e as many times higherthan that of the

spin"le as its-spin"le. pitch is smaller than that of the screw to $e c!t


131/151

spin"le as its-spin"le. pitch is smallerthan that of the screw to $e c!t%

he spee" of the lea" screw will $e as many times lowerthan that of

the spin"le as its-spin"le. pitch is greater than that of the screw to $e

c!t%

o effect this (ariations in spee"s, change gears are employe" an"

the amo!nt $y which the spee" of the lea" screw sho!l" $e higher or

lower than that of the work "etermineswhat is known as gearing ratio%

o calc!late the gears re/!ire" for c!tting a threa" of certain pitch can

calc!late" from the following form!la@

%alculation o! %hange .ears


132/151

calc!late" from the following form!la@

he gear of the spin"le shaft is the "ri(er an" the gear on the lea"screwis the "ri(en gear%

Note:Engine lathes are equipped with a set of gears ranging fro

!" to #!" teeth in steps of $ teeth, and one gear with #!% teeth

(&ranslating gear) for cutting etric threads.

screw$!!riven%leaonteethof&o#

gear$!!river%stuonteethof&o#

threa!sscrewlea!oflea!

cut'etoscrewtheoflea!

(o'on)*I

screwlea!on)*I

screwlea!ofpitch

cut'etoscrewof

worktheofspee!

screwlea!ofspee!ratio

=

=

=

=

=

pitch

Gear

(election o! .ear Train

L " ' i


133/151

Lea" screwK'ri(en

*pin"leK'ri(er

Interme"iate gears or i"le gears has no effect on spee" ration%

Hse" only to fill the gap $etween "ri(er an" "ri(en an" to o$tain a

"esire" "irection of the lea" screw%

To cut Metric thread on Metric leadscre"3


134/151

he c!tting of metric threa" -mm. on a lathe with an etric -mm.

lea"screw

+river teeth *itch of the screw to 'e cut in mm

+riven teeth *itch of the lea! screw in mm

=

To cut English threads8inch9 on Metric leadscre"8009


135/151

+river teeth *itch of the screw to 'e cut in inches

+riven teeth *itch of the lea! screw in mm

*itch of the screw to 'e cut in inches 25#,mm

*itch of the lea! screw in mm

=

=

*itch of the screw to 'e cut in inches %12- . 5$ /

*itch of the lea! screw in imm

12- *itch of the screw to 'e cut in inches5 *itch of the lea! screw in mm

=

6 inch K


136/151

Where

Pc K Pitch to $e c!t in mm

PLK Pitch of lea" screw in inches

n K 2o% of starts

"

c

"

c

12-*

*5*12-

*5n==

1ear ratioK

Where

PcK Pitch to $e c!t in inches

PLKPitch of lea" screw in mm)*I#

1

ofNoPitch =

startsofno#

lea!=Pitch"

c

*5

*12-n

To cut Metric thread on English leadscre"s3

he c!tting of metric threa" -mm. on a lathe with an English -inch.

lea"screw may $e carrie" o!t $y intro"!cing a translating gear of 6


137/151

lea"screw may $e carrie" o!t $y intro"!cing a translating gear of 6


138/151

g p

0

30

30

30

3

1

-5

25

25

25

3

1

0

20

20

20

3

1

2

cut'epitch to

ratio ======== xxxscrewleadofpitchGear

Pro$lem@

Download - Lathe Part I

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