Lathe operations

LatheLathe Operations Operations LatheLathe Operations Operations

Chapter 4

L a t h e

Turning Turning OperationsOperations

Turning Turning OperationsOperations

Machine Tool – LATHE Job (workpiece) – rotary motionTool – linear motions

“Mother of Machine Tools “Cylindrical and flat surfaces

Some Typical Lathe Some Typical Lathe JobsJobs

Some Typical Lathe Some Typical Lathe JobsJobs

Turning/Drilling/Grooving/Threading/Knurling/Facing...

LatheLathe LatheLathe


Bed

Head StockTail Stock

CarriageFeed/Lead Screw


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Lathe BedLathe BedLathe BedLathe Bed

Heavy, rugged castingMade to support working parts of

latheOn top section are machined ways

Guide and align major parts of lathe

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Lathe BedLathe BedLathe BedLathe Bed

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HeadstockHeadstockHeadstockHeadstock Clamped on left-hand end of bed Headstock spindle

Hollow cylindrical shaft supported by bearingsProvides drive through gears to

work-holding devicesLive center, faceplate, or chuck fitted

to spindle nose to hold and drive work Driven by stepped pulley or transmission

gears Feed reverse lever :Reverses rotation of

feed rod and lead screw

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HeadstockHeadstockHeadstockHeadstock

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Quick-Change GearboxQuick-Change GearboxQuick-Change GearboxQuick-Change Gearbox Contains number of different-size

gears Provides feed rod and lead-screw with

various speeds for turning and thread-cutting operationsFeed rod advances carriage when

automatic feed lever engagedLead screw advances the carriage

for thread-cutting operations when split-nut lever engaged

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Quick-Change GearboxQuick-Change GearboxQuick-Change GearboxQuick-Change Gearbox

Top View

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CarriageCarriageCarriageCarriageUsed to move cutting tool along lathe

bedConsists of three main parts

SaddleH-shaped casting mounted on top of lathe ways, provides means of mounting cross-slide and apron

Cross-slideApron

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CarriageCarriageCarriageCarriage

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Cross-slideCross-slideCross-slideCross-slide 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 toolSwiveled to any angle for taper-turningHas graduated collar that ensure

accurate cutting-tool settings (.001 in.) (also cross-slide)

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Cross-slideCross-slideCross-slideCross-slide

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ApronApronApronApron 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 hand wheel turned manually to move carriage along lathe bed

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Apron

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Automatic Feed Automatic Feed LeverLever

Automatic Feed Automatic Feed LeverLever

Engages clutch that provides automatic feed to carriage

Feed-change lever can be set for longitudinal feed or for crossfeed In neutral position, permits split-nut

lever to be engaged for thread cutting

Carriage moved automatically when split-nut lever engaged

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TailstockTailstockTailstockTailstock Upper and lower tailstock castings 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 centerProvides support for right-hand end of

work

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Tailstock

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Setting Speeds on a LatheSetting Speeds on a LatheSetting Speeds on a LatheSetting Speeds on a Lathe Speeds measured in revolutions per

minute Belt-driven lathe

Various speeds obtained by changing flat belt and back gear drive

Geared-head latheSpeeds changed by moving speed

levers into proper positions according to r/min chart fastened to headstock

Types of LathesTypes of LathesTypes of LathesTypes of LathesEngine Lathe

Tool Room Lathe Gap Bed Lathe Capstun lathe

Turret latheSpeed LatheBench Lathe

Special Purpose Lathe

…

Specifications of Specifications of LatheLathe


Workpiece Length Swing

Example: 300 - 1500 LatheMaximum Diameter of

Workpiece that can be machined = SWING (= 300 mm)

Maximum Length of Workpiece that can be held between Centers (=1500 mm)



WorkholdingWorkholding DevicesDevices

WorkholdingWorkholding DevicesDevices

Equipment used to holdWorkpiece – fixturesTool - jigs

Securely HOLD or Support while machining

Three jaw chuckThree jaw chuck Three jaw chuckThree jaw chuck

- For holding - For holding cylindrical stock cylindrical stock centered.centered.- For facing/center - For facing/center drilling the end of drilling the end of your aluminum stockyour aluminum stock

Four-Jaw Chuck

- This is independent chuck generally has four jaws , which are adjusted individually on the chuck face by means of adjusting screws

ChucksChucksChucksChucksThree jaw Four Jaw

Work

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Thin jobs can be held by

means of magnetic chucks.

Collet Chuck

Magnetic Chuck

Collet chuck is Collet chuck is used to hold used to hold small workpiecessmall workpieces

Thin jobs can be Thin jobs can be held by means of held by means of magnetic chucks.magnetic chucks.

CentersCentersCentersCentersW

ork

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FaceplatesFaceplatesFaceplatesFaceplatesW

ork

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W

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DogsDogsDogsDogsW

ork

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W

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MandrelsMandrelsMandrelsMandrelsWorkpiece (job) with a hole

Work

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RestsRestsW

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Steady Rest Follower Rest

Operating/Cutting Operating/Cutting ConditionsConditions

Operating/Cutting Operating/Cutting ConditionsConditions

1. Cutting Speed v2. Feed f3. Depth of Cut d

Operating Operating ConditionsConditionsOperating Operating ConditionsConditions

NDSspeedperipheral

D

rotation1intraveltoolrelative

Cutting SpeedCutting SpeedCutting SpeedCutting Speed

The Peripheral Speed of Workpiece past the Cutting Tool

=Cutting SpeedOp

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m/min1000

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D – Diameter (mm)N – Revolutions per Minute (rpm)

FeedFeedFeedFeed f – the distance the tool

advances for every rotation of workpiece (mm/rev)

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Depth of CutDepth of CutDepth of CutDepth of Cut perpendicular distance

between machined surface and uncut surface of the Workpiece

d = (D1 – D2)/2 (mm)

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3 Operating 3 Operating ConditionsConditions

3 Operating 3 Operating ConditionsConditions

Selection of .. Selection of .. Selection of .. Selection of ..

Workpiece Material Tool MaterialTool signature Surface FinishAccuracy Capability of Machine Tool

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Material Removal Material Removal RateRate

Material Removal Material Removal RateRate

MRRMRRVolume of material removed in one

revolution MRR = D d f mm3

• Job makes N revolutions/min

MRR = D d f N (mm3/min)

In terms of v MRR is given byMRR = 1000 v d f (mm3/min)O

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Operations on Operations on LatheLathe

Operations on Operations on LatheLathe

TurningFacingknurlingGroovingParting

ChamferingTaper

turningDrillingThreading

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Lathe OperationsLathe OperationsLathe OperationsLathe Operations

TurningTurningTurningTurningO

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Turning ..Turning ..Turning ..Turning ..Cylindrical job

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Turning ..Turning ..Turning ..Turning ..

Excess Material is removed to reduce Diameter

Cutting Tool: Turning Tool

a depth of cut of 1 mm will reduce diameter by 2 mm

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FacingFacing FacingFacingFlat Surface/Reduce length

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Facing ..Facing ..Facing ..Facing .. machine end of job Flat surface

or to Reduce Length of Job Turning Tool Feed: in direction perpendicular to

workpiece axisLength of Tool Travel = radius of workpiece

Depth of Cut: in direction parallel to workpiece axis

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Facing ..Facing ..Facing ..Facing ..O

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Eccentric TurningEccentric TurningEccentric TurningEccentric TurningO

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KnurlingKnurlingKnurlingKnurlingProduce rough textured

surfaceFor Decorative and/or Functional Purpose

Knurling Tool

A Forming ProcessMRR~0

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KnurlingKnurlingKnurlingKnurlingO

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Knurling ..Knurling ..Knurling ..Knurling ..O

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GroovingGroovingGroovingGroovingProduces a Groove on workpiece

Shape of tool shape of groove

Carried out using Grooving Tool A form tool

Also called Form Turning

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Grooving ..Grooving ..Grooving ..Grooving ..O

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PartingPartingPartingPartingCutting workpiece into TwoSimilar to groovingParting ToolHogging – tool rides over –

at slow feedCoolant use

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Parting ..Parting ..Parting ..Parting ..O

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ChamferingChamferingChamferingChamferingO

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ChamferingChamferingChamferingChamfering Beveling sharp machined

edges Similar to form turning Chamfering tool – 45° To

Avoid Sharp Edges Make Assembly Easier Improve AestheticsO

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Taper TurningTaper TurningTaper TurningTaper TurningTaper:

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Taper Turning..Taper Turning..Taper Turning..Taper Turning..

MethodsMethods Form Tool Swiveling Compound Rest Taper Turning AttachmentOffsetting tailstock Simultaneous Longitudinal and

Cross Feeds

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Taper TurningTaper Turning .. ..By Form ToolBy Form ToolTaper TurningTaper Turning .. ..By Form ToolBy Form Tool

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Taper Turning ,,Taper Turning ,,

By Compound RestBy Compound RestTaper Turning ,,Taper Turning ,,

By Compound RestBy Compound RestO

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Tailstock Offset Tailstock Offset MethodMethod

Tailstock Offset Tailstock Offset MethodMethod

Generally used to cut taper when no taper attachment available

Involves moving tailstock center out of line with headstock centerAmount tailstock may be offset

limited Will not permit steep tapers to be

turned or standard tapers turned on end of long piece of work

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Procedure to Offset Procedure to Offset Tailstock by the Visual Tailstock by the Visual

MethodMethod

Procedure to Offset Procedure to Offset Tailstock by the Visual Tailstock by the Visual

MethodMethod

Loosen the tailstock clamp nut Offset upper part of tailstock by loosening

one setscrew and tightening the other until required amount is indicated on graduated scale at end of tailstock

Note: Make sure both setscrews snugged up to prevent any lateral movement of tailstock

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Procedure to Offset the Procedure to Offset the Tailstock AccuratelyTailstock Accurately

Procedure to Offset the Procedure to Offset the Tailstock AccuratelyTailstock Accurately

1. Adjust tailstock spindle to distance it will be used in machining setup and lock tailstock spindle clamp

2. Mount a dial indicator in toolpost with plunger in horizontal position and on center

3. Using crossfeed handle, move indicator so registers ~.020 in on work, and set indicator and crossfeed graduated collars to zero

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4. Loosen tailstock clamp nut5. With tailstock adjusting setscrews, move

tailstock until required offset shown on dial indicator

6. Tighten tailstock setscrew that was loosened, making sure indicator reading does not change

7. Tighten tailstock clamp nut

Note: Tailstock may also be offset by using feeler gage between toolpost and tailstock spindle in conjunction with crossfeed graduated collar

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Plain Taper Plain Taper AttachmentAttachmentPlain Taper Plain Taper AttachmentAttachment

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Procedure to Taper Using a Procedure to Taper Using a Taper AttachmentTaper Attachment

Procedure to Taper Using a Procedure to Taper Using a Taper AttachmentTaper Attachment

1. Clean and oil guide bar2. Loosen lock screws and offset end of guide

bar the required amount or, for inch attachments, set bar to required taper in degrees .

3. Tighten lock screws4. With compound rest set at 90º, set up

cutting tool on center

DrillingDrillingDrillingDrillingDrill – cutting tool – held in TS – feed from TS

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Cutting Cutting Screw Screw

ThreadsThreads

Cutting Cutting Screw Screw

ThreadsThreads

: (a) Standard nomenclature for screw threads,

(b) Unified National thread and identification of threads,

(c) ISO metric thread and identification of threads.

Screw-Thread Nomenclature

Standardization of screw threads began in the middle 1880’s

Cutting Screw Cutting Screw ThreadsThreads


Design Considerations for Screw-Thread Cutting

Should allow for the termination of threads before they reach a shoulder

Eliminate shallow, blind tapped hole Chamfers should be specified at the ends Threaded sections should not be interrupted with

slots, holes, or other discontinuities Use standard tooling for threads Operations should be completed in one step



Fig : (a) Cutting screw threads on a lathe with a single-point cutting tool. (b) Cutting screw threads with a single-point tool in several passes, normally utilized for large threads. The small arrows in the figures show the direction of feed, and the broken lines show the position of the cutting tool as time progresses. (c) A typical carbide insert and tool holder for cutting screw threads. (d) Cutting internal screw threads with a carbide insert.

Types of Screw threadsTypes of Screw threadsTypes of Screw threadsTypes of Screw threads

Fig : Various types of screw threads

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Thread-Chasing dialThread-Chasing dialThread-Chasing dialThread-Chasing dial

Lathe spindle and lead screw must bein same relative position for each cut Thread-chasing dial

attached to carriage forthis purpose

Dial has eight divisions Even threads use any

division Odd threads either

numberedor unnumbered: not both

Process SequenceProcess Sequence Process SequenceProcess SequenceHow to make job from raw

material 45 long x 30 dia.?

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Steps:•Operations•Sequence•Tools•Process

Process Sequence ..Process Sequence .. Possible SequencesProcess Sequence ..Process Sequence ..

Possible Sequences TURNING - FACING - KNURLING TURNING - KNURLING - FACING FACING - TURNING - KNURLING FACING - KNURLING - TURNING KNURLING - FACING - TURNING KNURLING - TURNING – FACINGWhat is an Optimal

Sequence?Op

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Machining TimeMachining TimeMachining TimeMachining Time

Turning Time Job length Lj mmFeed f mm/rev Job speed N rpmf N mm/min

min Nf

Lt j

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Manufacturing TimeManufacturing TimeManufacturing TimeManufacturing Time

Manufacturing Time = Machining Time + Setup Time + Moving Time + Waiting Time

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ExamplesExamplesExamplesExamples(1)A mild steel rod having 50 mm diameter and

500 mm length is to be turned on a lathe. Determine the machining time to reduce the rod to 45 mm in one pass when cutting speed is 30 m/min and a feed of 0.7 mm/rev is used.

Given data: D = 50 mm, Lj = 500 mm v = 30 m/min, f = 0.7 mm/rev

Substituting the values of v and D in

calculate the required spindle speed as: N = 191 rpm

m/min1000

NDv

Machining time:

min Nf

Lt j

t = 500 / (0.7191) = 3.74 minutes

ExampleExampleExampleExample(2)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.

Given data: D1 = 80 mm, D2 = 50 mm, Lj = 80 mm (with usual notations)

tan = (80-50) / 280 or = 10.620 The compound rest should be swiveled at 10.62o

ExampleExampleExampleExample(3)A 150 mm long 12 mm diameter stainless steel

rod is to be reduced in diameter to 10 mm by turning on a lathe in one pass. The spindle rotates at 500 rpm, and the tool is traveling at an axial speed of 200 mm/min. Calculate the cutting speed, material removal rate and the time

required for machining the steel rod. Given data: Lj = 150 mm, D1 = 12 mm, D2 =

10mm, N = 500 rpm Using Equation …………………….

v = 12500 / 1000 = 18.85 m/min.

depth of cut = d = (12 – 10)/2 = 1 mm

m/min1000

NDv

feed rate = 200 mm/min, we get the feed f in mm/rev by dividing feed

rate by spindle rpm. That is f = 200/500 = 0.4 mm/rev From Equation ,MRR = D d f N (mm3/min)

MRR = 3.142120.41500 = 7538.4 mm3/min from Equation …………….

t = 150/(0.4500) = 0.75 min.

min Nf

Lt j

Calculation of the machining time

when there is more than one operation?

ExampleExampleExampleExample(4)Calculate the time required to machine a

workpiece 170 mm long, 60 mm diameter to 165 mm long 50 mm diameter. The workpiece rotates at 440 rpm, feed is 0.3 mm/rev and maximum depth of cut is 2 mm. Assume total approach and overtravel distance as 5 mm for turning operation.

Given data: Lj = 170 mm, D1 = 60 mm, D2 = 50mm,

N = 440 rpm, f = 0.3 mm/rev, d= 2 mm

Time for Turning:

Total length of tool travel = job length + length of approach and over-travel L = 170 + 5 = 175 mm Depth to be cut d= (60 – 50)/2 = 5 mm Since maximum depth of cut is 2 mm, 5 mm

cannot be cut in one pass. Therefore, we calculate number of cuts or passes required.

Number of cuts = 5/2 = 2.5 = 3(since cuts cannot be a fraction) Machining time for one cut = L / (fN) Total turning time = [L / (fN)] Number of cuts = [175/(0.3440)] 3 = 3.97 min.

Time for facing:Now, the diameter of the job is reduced to 50 mm. Recall that in case of facing operations, length of tool travel is equal to half the diameter of the job.

That is, l = 25 mm. Substituting in equation , we get

t = 25/(0.3440) = 0.18 min.

Total time: Total time for machining = Turning Time + Facing

Time = 3.97 + 0.18 = 4.15 min.

min Nf

Lt j

ExampleExampleExampleExampleWrite the process sequence

to be used for manufacturing the component from raw material of 175 mm length and 60 mm diameter

ExampleExampleExampleExample

ExampleExampleExampleExample To write the process sequence, first list the

operations to be performed. The raw material is

having size of 175 mm length and 60 mm

diameter. The component shown in Figure 5.23 is

having major diameter of 50 mm, step diameter of

40 mm, groove of 20 mm and threading for a

length of 50 mm. The total length of job is

160 mm. Hence, the list of operations to be carried

out on the job are turning, facing, thread cutting,

grooving and step turning

ExampleExampleExampleExample A possible sequence for producing

the component would be: Turning (reducing completely to 50

mm) Facing (to reduce the length to 160

mm) Step turning (reducing from 50 mm

to 40 mm) Thread cutting. Grooving