Metal Cutting

Unit III
 Machine Tools

• A power driven machine for making a given

shape, size and accuracy by removing the
metal from the work pieces in the form of
chips against the cutting tool

• Factory equipment to produce machine,

equipment and tools
 Machine Tools

• Machine tools perform

– To hold the job
– To hold the cutting tool
– To move one or both of these
– To provide a feeding motion for one of
these
 Machine Tools Classification

• Field of application

– General purpose machine

– Single purpose machine

– Limited purpose machine

– Production machine tools

– Specialized machine tools

 Machine Tools Classification

• Weight
– Low weight (up to 1ton)
– Medium weight (up to 10 ton)
– High weight (over 10 ton)
 Machine Tools Classification

• Accuracy
– Normal accuracy
– Higher accuracy
– Precision
– High precision
– Super high precision
 Machine Tools Classification
• Types of processing
- Lathe machine
- Drilling, Boring machine
- Planer, shaper, slotter , broaching machine
- Milling machine
- Grinding machine, micro finishing machine
- Gear and thread cutting machine
- Combination machine tools
- Cutting off machines
- Miscellaneous machine tools
 Lathe
• Oldest of all the machine tools

• Most important in modern production

• It is defined as a machine tool which removes

the material from the rotating work against a
cutting tool

• Used for cylindrical work generally

 Lathe types
• Speed lathe
– Wood working lathe
– Centering lathe
– Metal spinning lathe
– Polishing lathe
• Engine lathe
– Belt drive
– Gear head drive
– Individual motor drive
• Bench lathe
• Tool room lathe
 Lathe types
• Semi-automatic lathe
– Capstan lathe
– Turret lathe
• Automatic lathe
• Special purpose lathe
– Wheel lathe
– Gap bed lathe
– Crank shaft lathe
– Duplicating lathe
• Copying lathe
Wood working lathe
 Metal
Spinning Lathe
Lathe
Lathe
 Lathe specifications
• The length of the bed
• The length between centers
• The height of the centers from the bed
• Max. diameter of bar stock that can be passed
through the hole of the main spindle
• Maximum swing over the bed
• Maximum swing over the carriage
Lathe specifications
 Principal Lathe parts
• Bed (C.I alloyed with Ni & Cr)
• Head stock (Carbon or Ni-Cr steel)
• Tail stock
• Carriage
• Feed mechanism
• Apron mechanism
Lathe components
Headstock
 Bed

• Base of lathe – box type

• Supports all parts of lathe
• Top of bed is accurately machined
• Head stock – left end, Tailstock – right end
• Made of cast iron alloyed with Ni & Cr
• Rigid and massive to absorb vibration, to resist
twisting stress
 Head stock
• Head stock (Carbon or Ni-Cr
steel)
– Back geared head stock
– All geared head stock
• Sliding gear mechanism
• Sliding clutch mechanism
• Combined sliding gear &
sliding clutch mechanism

Provide 9 different speed

Back gear
Back gear mechanism
All geared headstock - Slide gear drive
All geared headstock • Demerits
- Slide gear drive • Costlier
• Power loss
• Motor and other parts
may get damaged at the
time of overloading
• Advantages
– Wide range of speed
– Power available in the tool
is constant
– Easy spindle speed change
– Belt shifting is eliminated
– Vibration of the spindle is
reduced
 Tail stock
• Functions of Tail stock
– Supports the one end of the work
– Holds the tool like drill, reamer, tap etc
– To do taper turning by off set method
– Some times support the work
Tail stock
 Carriage
• Saddle
• Cross slide
• Compound slide
• Tool post
• Apron

APRON

Tool post
 Lathe Carriage and Apron
Tool Post
Compound
Rest Carriage
Cross Lock
Feed Cross Screw
Apron Knob Slide
Hand Apron Feed
Wheel Change
Lever

Half Nut
Lever

Power
Feed Compound
Clutch Rest Knob
 Apron Hand Wheel
Used to move tool along the work - for Turning (Longitudinal
Feed)

Apron
Hand
Wheel

38
 Cross Feed Knob
Used to move cutting tool across the end of the stock -
Facing (Cross Feed)

Cross
Feed
Knob

39
 Power Feed Clutch
Engages the power feed for turning or facing
operations

Power
Feed
Clutch
40
 Feed mechanism
• Feed – the movement of the tool relative to
the work piece
• Feed – automatic or hand
• Feed
– parallel to lathe axis (longitudinal feed)
– Perpendicular to the lathe axis (cross feed)
– Angular to the lathe axis (Angular feed)
 Feed mechanism

Feed – automatic
• Tumbler gear mechanism
• Change gear train
• Quick change gear box
• Lead screw and feed rod
• Apron mechanism
 Tumbler gear feed reversing mechanism
Downward Neutral Upward
Tumbler gear feed reversing mechanism
Tumbler gear feed reversing
mechanism
Tumbler Gear Reverse Mechanism
Introduction to types of gears

Worm gear

Rack and pinion Spur gear

Apron mechanism
Sliding key mechanism
 Work holding devices

• Chucks
• Centers
• Face plates
• Mandrels
• Angle plates
• Fixtures
 Chucks
• 3 jaw chuck (Self centering chuck)
• 4 jaw chuck (Independent chuck)
• Magnetic chuck
• Collet chuck
3 Jaw chuck
3 Jaw Chuck
4 Jaw Chuck
Magnetic chuck
Spring collet chuck

Collet
 Centers
• Function of centers
– To support work piece
– To act as a solid bearing
• High grade tool steel
• Hardened and ground taper to an angle of 60°
 Centers
• Shanks are machined to Morse taper
• Main spindle: LIVE CENTER
• Tail stock: DEAD CENTER
 Types of Centers
• Ordinary center
• Half center
• Ball center
• Tipped center
• Inserted type center
• Pipe center
• Frictionless center
(revolving center)
Centers
 Face plate
Function of faceplate:
To hold the work piece by bolts and clamps
To hold the irregular job
To hold the eccentric jobs, angular plates etc.
Face plate
Face plate with job
Face plate with job
 Types of dog or carrier

Straight tail dog Bent tail dog

Safety clamp lathe dog Heavy duty lathe dog

Catch plate with dog
Catch plate with dog
 Turning between centers

Faceplate with Job

threaded peg

Live centre
Lathe
with Morse
carrier
sleeve
 Mandrels
• To hold the hollow job
• Job is fitted over mandrel and mandrel is fitted
between centers
• Different mandrels for different jobs
Workpiece Mandrel
 Types of Mandrels

Plain Mandrels Expanding Mandrels

 Types of Mandrels

Gang Mandrels Stub Mandrels

Types of Mandrels
 Steady rest
• For machining long work piece, steady or
follower rest is used: L/D > 10 or 12
• Avoids the deflection of work piece and bending
of work piece
• Types:
1. Fixed type 2. Follower type
Steady rest Follower rest
 Steady rest Follower rest

Jaws
Work Work Jaws
Hinge

Carriage

Lathe bed guideways

 Lathe operations
• Facing
• Turning (plain, step, taper, eccentric turning)
• Drilling, Reaming, Boring
• Knurling
• Parting off
• Shouldering ( Square, beveled, radius, undercut)
• Forming (concave, convex, end radius), Grooving
• Chamfering
• Tapping
• Thread cutting
• Milling
• Grinding
Single point cutting tool
Single point cutting tool
Setting the Tool
Center drilling or Counter sinking
Center drilling
 Cutting conditions
Cutting speed
Feed
Depth of cut
Cutting speed
Workpiece
Depth of cut (d)
N
Machined
surface
Chuck Feed (f ) Chip
Tool Depth of cut
 Facing
Flat Surface/Reduce length

Chuck Workpiece
d
Machined
Face
Cutting
speed Depth of
cut
Tool Feed
Facing
 Turning
Cylindrical job

Workpiece
Cutting
speed Depth of cut (d)
N
Machined
surface
Chuck Feed Chip
Tool
Depth of cut
Turning
Automatic turning
Step Turning
 Eccentric Turning

4-jaw Axis of job

chuck

Axis o

Cutting Eccentric peg

speed (to be turned)
 Knurling

Knurled surface
Cutting
speed
Feed Movement
for depth
Knurling tool
Tool post
Knurling
 Grooving

Shape produced
by form tool Groove

Feed or Grooving
Form tool depth of cut tool
Forming
 Parting off

Feed
Parting tool
 Chamfering

Chamfer

Feed
Chamfering tool
 Drilling
Drill – cutting tool – held in TS – feed from TS
Quill
Drill clamp moving
quill
Tail stock
Feed
Tail stock clamp
Hand Tapping on the Lathe
Reaming
Boring
 Taper Turning

D1  D2
tan  
2L

90°
D1  D2

B  C

A L
 Taper Turning
Methods
• Form Tool
• Swiveling Compound Rest
• Taper Turning Attachment
• Simultaneous Longitudinal and Cross Feeds
• Setting over the tail stock centre
 Taper Turning ..
By Form Tool

Workpiece Taper


Form Direction
Straight of feed
cutting edge tool
 Taper Turning , by Compound Rest
Dog
Mandrel Tail stock quill

Tail stock

Face plate Direction of feed

Tool post & Compound rest
Tool holder Slide
Compound rest
Cross slide  Hand crank
TAPER TURNING ATTACHMENT
 TAIL STOCK SET OVER METHOD

• Tailstock set lover = L x (D-d)/2l

• Ө = tan-1 (D-d/2l)

• Where D = diameter of the large end of job

d = diameter of the small end of job
l = length of the taper of cylindrical job
L = Total length of the Job
 Thread cutting operation

• Making square or Screw Thread Terminology

‘V’ helical groove
• External/Internal
• External die/tool
• Tap/tool
• Tool – automatic
feed
Tap & Die
 Thread cutting operation
During thread cutting:

The longitudinal movement of tool

= lead of the screw to be cut per revolution
of job

where Lead is the axial distance moved by screw

per revolution screw.
 Thread cutting operation

Gear ratio = Lead screw turn/spindle turn

= pitch of the work/pitch of lead
screw
= driver gear/driven gear
= spindle gear/ lead screw gear

Sets of gears: 20 to 120 in steps of 5 teeth and 127

teeth gear
 Thread cutting operation

Gear Train:
Simple/Compound gear train
Gear ratio for cutting metric thread
= 5pn/127;
p – pitch,
n – threads per inch in lead screw
 Thread cutting
Thread cutting speed = ¼th of speed of turning
 Thread cutting
• Thread catching: engaging tool with the same groove in
all the cuts
– Reversing the machine
– Using a chasing dial
 Thread cutting

• Right hand thread/Left hand thread

• Single start/multiple start thread

• Pitch for multi start thread = Lead/no. of starts

• Gear ratio for multi start thread

= Lead of work/Lead of lead screw

Thread cutting