Lathe Machine Tool

1. Department of Mechanical Engineering
National Institute of Technology Sikkim
Lathe

2. Content
 Safetyprecautions on the lathe
 Typesof Lathe
 Specification and purposeof the centrelathe
 Identify main parts of the Centre lathe
 Statethe purposeof eachmainparts
 Method of Holdingwork
 Method of cuttingtapers
 Cuttingspeedon theLathe
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3. SafetyPrecautions
 Alwayswearapprovedsafetyglasses
 Rollupsleeves,removetie andtuck inloose
clothing
 Neveroperate machineif safetyguards
areremoved
 Stoplathe before measurework or clean,oil
or adjustmachine
 Alwaysremovechuckkeyafteruse
 Alwaysremovechipswithbrush
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4. Types of Lathe
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Bench Lathe Center Lathe Capstan Lathe

5. Types of Lathe
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Turret Lathe CNC Lathe

6. CentreLathe
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A lathe center, often
shortened to center, is a tool
that has been ground to a
point to accurately position a
workpiece on an axis. They
usually have an included
angle of 60°, but in heavy
machining situations an
angle of 75° is used.

7. LatheParts
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8. Department of Mechanical Engineering
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HeadStock

9.  Clamped on left-hand end of bed.
 Headstock spindle
• Hollow cylindrical shaft supported by
bearing
• Provides drive through gears to work-
holding devices
• Live center, faceplate, or chuck fitted to
spindle nose to hold and drive work
 Driven by stepped pulley or transmission gears.
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National Institute of Technology Sikkim
HeadStock

10. Department of Mechanical Engineering
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LatheBed
 Heavy, rugged casting
 Made to support working
parts of lathe
 On top section are machined
ways- Guide and align major
parts oflathe

11. Department of Mechanical Engineering
National Institute of Technology Sikkim
• Used to move cutting tool along lathe bed
• Consists of main parts
– Saddle H-shaped casting mounted on top of
lathe ways, provides means of mounting
cross-slide and apron
– Compound Rest
– Cross-slide
– Apron
– Tool Post
Carriage

12. Department of Mechanical Engineering
National Institute of Technology Sikkim
• Fastened to saddle
• Houses gears and mechanism required to
move carriage or cross-slide automatically
• Locking-off lever inside apron
prevents engaging split-nut lever and
automatic feed lever at same time
• Apron handwheel turned manually
to move carriage along lathe bed
Apron

13. Department of Mechanical Engineering
National Institute of Technology Sikkim
CrossSlide
• Mounted on top of saddle
• Provides manual or automatic
cross movement for cutting tool
• Compound rest (fitted on top of
cross- slide)
– Used to support cutting tool
– Swiveled to any angle for taper-
turning
– Has graduated collar that ensure
accurate cutting-tool settings (.001
in.) (also cross-slide)

14. It is fixed on top of the cross-
slide, and can be turned (set)
to any desired angle. The
compound slide is useful for
turning and boring short
tapersand chamfers.
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Compoundslide/Topslide

15. • Therearethreemaintypesoftool postused for holdinglathe cuttingtools:
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ToolPost
Ring and rocker Four-way turret Quick -change

16. Department of Mechanical Engineering
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TailStock
 Adjusted for taper or parallel turning
by two screws set in base
 Tailstock clamp locks tailstock in
any position along bed of lathe
 Tailstock spindle has internal taper
to receive dead center provides
support for right-hand endof work

17.  Producecylindricalwork
 Typeof lathe Programmeto carry
outtask
 Useto tighten thechuck
 Typesof lathe useinschool
workshops
 Useto makeprecisionwork and
smallworkpieces.
 lathe which havemultiple tools
 Toolpost that doesn’tneed
packing
 Useto produce shorttapers
 Made to support working parts of
lathe
 Foundat the left sideofthe bed
Foundat the right sideof the bed
Holdfour tools at the same time
Used to move cutting tool along
lathe bed
 Parts of the machine use when
facing off
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Quizpoints

18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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 Swing- the largest work
diameter that can be swung
for the lathe bed.
 The distance between the
headstock and tailstock
center.
 Length of the bed in a meter.
 The pitch of the lead screw.
 Horsepower of the machine.
 Speed range and the number
of speeds of HS spindle.
LatheSpecification

19. • The cutting speed (v) of a tool is the speed at which the metal is removed by the tool from
the workpiece. In a lathe, it is the peripherical speed of the work past the cutting tool
expressed in meters per minute.
• The feeds(f) of the cutting tool in lathe work are the distance the tool advances for each
revolution of the work. A feed is expressed in millimeters per revolution.
• The depth of cut (d) is the perpendicular distance measured from the machined surface
to the uncut surface of the workpiece. The depth of cut changes inversely as the cutting
speed. For general purpose, the ratio of the depth of cut to the feed varies from 10:1.
• The machining time (t) is the time by which machining process is completed. Time for the
lathe work can be calculated for a particular operation if the speed of the job, feed and
length of the job is known.
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MachiningParameters

20. 47-42
• Rate at which point on work circumference travels past
cutting tool
• expressed in meters per minute (m/min)
• Important to use correct speed for material
–Too high: cutting-tool breaks down rapidly
–Too low: time lost, low production rates
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CuttingSpeed

21. • The softer the work
material, the faster
the recommended
cutting speed
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Cuttingspeedselection
• The harder the cutting tool
material, the faster the cutting
speed. The softer the cutting
tool material, the slower the
recommended cutting speed

22. • The material being cut
• The rigidity and condition of the machine
• The material of which the tool is made from
• The depth of cut and the feed rate
• Availability of coolant (cutting fluid)
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FactorsthatDeterminecuttingspeed

23. Material beingcut
Cuttingspeed
(metres/minute)
Mildsteel Cast
iron
Highcarbonsteel
Brass
Bronze
Aluminium
20to28
18to25
12to18
45to90
15to21
Upto300
47-49
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LatheCuttingSpeedsfordifferentMaterials

24. 47-50
• Given in metres per minute
• spindle speed of machine (N) and diameter of
work must be known
S (m/min)= πDN/1000
• Where π= 22/7 or 3.142
D= diameter of material in mm.
N= Spindle speed(rev/min)
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CalculatingLathecuttingspeed

25. • Calculate rev/min required to rough-turn 150mm diameter piece of
machinesteel(CS90)cuttingspeedis30m/min.
• Find the cutting speed of a 50mm diameter bar being turned with a
spindleof 178 rev/min.
Examples
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Exercise
• Calculate the spindle speed required to turn 200mm diameter piece of high
speed steel, if the cutting speed is 28 m/min.
• Find the cutting speed of a 15mm diameter bar being turned with a spindle
of 955 rev/min.
• Determine the lathe speed to cut a 40mm diameter at 30 m/min

26. 1. What is cutting speed for turning?
2. State the unit for cutting speed.
3. Which of the following materials have the highest
cutting speed.
1.Brass 2. Bronze 3. mild steel. Give
reasons for your choice.
4. List four factors that determine the cutting speed.
Explain any two factors.
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Classwork

27. •
Divided into twocategories
– Work-holding,-supporting, and–driving devices
• Lathecenters,chucks,faceplates
• Mandrels, steadyandfollowerrests
• Lathedogs,driveplates
– Cutting-tool-holding devices
• Straight andoffsettoolholders
• Threadingtoolholders, boringbars
• Turret-typetoolposts
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LatheAccessories

28. • Work to be turned between centers must have center hole
drilled in each end
• Support during cutting
• Most common have solid Morse taper
shank 60º centers, steel with carbide tips
• Care to adjust and lubricate occasionally
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LatheCenters

29. Lathe centres is used as a support at the end of a work. It is usually
madefrom carbon tool steel. Thereare three (3) main types of Lathe
centres:
 Livecentre (Revolvingcentre)
 Deadcentre
 Halfcentre
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TypeofLatheCentres

30.  It isconstructedsothat the60°centerrunsinits own bearings.
 Thelive centre fits in the spindle(headstock)and rotates with thespindle.
 Usedwhen turning betweencentres
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Livecentre(RevolvingCentre)
Centre in Headstock Spindle

31.  Fits in the tailstock spindle,
remains stationary while the
workrotatesonitspoint
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Deadcentre
Halfcenter
 A centre that is cut away almost to its
point. It isoften usedin the tailstockfor
facing up to or for turning close to the
endof thework.

32. Department of Mechanical Engineering
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• Usedextensivelyfor holding workfor
machiningoperations
– Work largeor unusualshape
• Most commonly usedlathechucks
– Three-jawuniversal
– Four-jawindependent
– Colletchuck
Chuck

33. • Holdsround andhexagonalwork
• Graspswork quickly andaccurate
• Threejawsmove simultaneously when adjustedbychuckKey
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Three-jawUniversalChuck

34.  Usedto hold round, square,
hexagonal,and irregularly shaped
workpieces
 Hasfour jaws
– Eachcanbeadjustedindependently by
chuckKey
 Jawscanbereversedto hold work
by inside diameter
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Four-JawIndependentChuck

35.  Collet chuck is used to
hold small
workpieces.
 Usedfor high-precisionwork
 Spring collets available to hold
round, square, or hexagon-
shapedworkpieces
 Each collet has range of only few
thousandths of an inch over or
undersizestampedon collet
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ColletChuck

36. |
Special adapter fitted into
taper of headstock spindle,
and hollow draw bar having
internal thread inserted in
opposite end of headstock
spindle. It draws collet
into tapered adapter causing
collet to tighten on
workpiece.
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ColletChuck

37.  A lathe dog ( lathe carrier) is a device that clamps
around the workpiece and allows the rotary motion
of the machine's spindle to be transmitted to the
workpiece.
 A carrier is most often used when turning between
centers on a lathe.
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LatheDogs/Carrier

38.  Standard bent-tail lathe dog
 Most commonly used for round workpieces
 Available with square-head setscrews of
headless setscrews
 Straight-tail lathe dog
 Driven by stud in driveplate
 Used in precision turning
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TypesofLatheDogs

39.  Safetyclamplathedog
 Usedto hold variety ofwork
 Widerangeofadjustment
 Clamplathe dog
 Widerrange thanothers
 Usedon allshapes
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TypesofLatheDogs

40. Department of Mechanical Engineering
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WorkHeldBetweenCentres

41. A faceplate is the basic workholding accessory for a lathe.
It is a circular metal plate which fixes to the end of the
lathe spindle. The workpiece is then clamped to the
faceplate, typically using t-nuts in slots in the faceplate, or
less commonly threaded holes in the faceplate itself.
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Faceplate
 Used to hold work too large or shaped so it
cannot be held in chuck or between centers
 Usually equipped with several slots to
permit use of bolts to secure work

42.  Used to support long work held in chuck or between lathe
centers
– Prevent springing
 Located on and aligned by ways of the lathe
 Positioned at any point along lathe bed
 Three jaws tipped with plastic, bronze or rollers may be
adjusted to support any work diameter with steadyrest
capacity
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SteadyRest/FixedSteady

43. Department of Mechanical Engineering
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SteadyRest

44.  Mounted on saddle
 Travels with carriage to prevent work from
springing up and away from cutting tool
 Cutting tool generally positioned just ahead of
follower rest
 Provide smooth bearing surface for two jaws
of follower rest
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TravellingSteady/FollowerRest

45. Department of Mechanical Engineering
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TravellingSteady

46. • Holds internally machined workpiece between centers so
further machining operations are concentric with bore
• Several types, but most common
– Plain mandrel
– Expanding mandrel
– Stepped mandrel
– Double cone mandrel
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Mandrel

47. Plain Mandrel
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TypesofMandrel
Expanding Mandrel

48. Department of Mechanical Engineering
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ColletChuck
TypesofMandrel
Stepped Mandrel Double cone Mandrel

49. Department of Mechanical Engineering
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TaperTurning
Taper Turning: A conical surface produced
on a lathe is called taper turning. The tool
moves at an angle to the axis of rotation.
Methods of Taper turning:
 Form tool method
 Compound rest method
 Taper attachment method
 Tailstock set over method

50. Department of Mechanical Engineering
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MethodsofTaperturning:
 Form tool method
It is one of the simplest methods used to produce
short taper. A broad nose tool having straight
cutting edge is set on to the work at half taper
angle and is fed straight into the work. It requires
excessive cutting pressure which may distort the
workpiece due to vibration.
 Compound rest method
This method is used to produce short and
steep taper. The compound rest is
swiveled to the required angle and
clamped in position, it can be moved up
to 45° on both sides.

51. Taper:
2L
tan  
D1 D2
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UsingthecompoundSlide

52. 105
d = small diameter
k = unit length of taper
l = total length of taper
D = large diameter
If know d, k, and l, D may be calculated.
D equal to small dia + amount of taper.
Amount of taper is equal to 1/k, so total
taper equals l/k.
D = d + total taper
D = d + l/k
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Metric Taper Calculations

53.  Calculate tailstock offset required to turn a 1:30 taper X 60 mm
long on a workpiece 300 mm long. The small diameter of tapered
section is 20 mm.
 Determine the angle at which the compound rest would be
swiveled for cutting a taper on a workpiece having a length of 150
mm and outside diameter 80 mm. The smallest diameter on the
tapered end of the rod should be 50 mm and the required length of
the tapered portion is 80 mm.
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TaperTurningCalculation

54. D  4 0
d  2 0
O L  1 0 5
l  5 0
D  5 0
d  2 0
O L  1 0 0
l  4 0
D  6 0
d  3 0
O L  1 2 0
l  6 0
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Usingthecompoundslide