Lathe-Types, Parts, Feed Mechanisms, Specifications,Lathe Accessories and Attachments,Lathe Operations

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LATHE MACHINE
MACHINE TOOLS
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The Lathe
 Lathe is a machine tool which holds the work
between two rigid and strong supports, called
centers, or in a chuck or face plate.
 The cutting tool is rigidly held and supported in
a tool post and is fed against the revolving
work.
 While the work revolves about its own axis, the
tool is made to move either parallel to
(Cylindrical surface) or at an angle with the
axis (Tapered surface) to cut the desired
material.
IntroductiontoEngineLathe

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Lathe Basics
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Parts of a Lathe
• Bed
• Head stock
• Tailstock
• Carriage
• Feed mechanism

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Lathe Basics
Headstock
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Lathe Basics
Bed

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Lathe Basics
Carriage/Apron
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Lathe Basics
Tailstock

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Figure: Diagram of an engine lathe, showing its principal components
Engine Lathe
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Lathe Basics
Cross
Slide
APRON
Half Nut
Lever Bed
TAILSTOCK
Carriage
Hand
Wheel
Tailstock
Spindle
Clamp
Feed
Change
Lever
Tool Post
Compound
Rest
Saddle
BED
WAYS
Motor
Drive
Gear
Box
Feed
Reverse
Lever
HEADSTOCK
Spindle
Nose
Lead
Screw

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Types of Lathe
1. Speed lathe
 Simplest of all types of lathe
 Contains Bed, Headstock, Tailstock, Tool post on adjustable slide
 No feed box, Lead screw, Carriage
 Headstock spindle speed:1200 to 3600 rpm
 Applications: Wood working, spinning, polishing etc.
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Types of Lathe …
2. Engine or Center lathe
 Most widely used
 Early lathes were driven by steam engines and so the name engine lathe
 Heavy duty
 Head stock is much more robust in construction
 Contains additional mechanism for multiple speeds
 Carriage, Feed rod and Lead screw are available and hence, longitudinal and
cross feeds are possible

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Machine Tools 13
Types of Lathe …
3. Bench lathe
 Small lathe, mounted on a bench
 Just a scaled version of engine
lathe
 Used for small and precision work
4. Tool room lathe
 Greater accuracy
 More versatility
 Wide range of speeds and feeds
 Applications:
Precision work on tools, dies,
gauges
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Capstan and Turret Lathes
 Tailstock of an engine lathe is
replaced by a hexagonal turret
 Several tools fitted on the turret
are fed into work in proper
sequence to carryout different
operations in one setting
 Hence used for production work
 Capstan lathe
Turret with its saddle can move
for a short distance over the sub
bed.
Limitation: Length of a job to
be machined is limited
 Turret lathe:
Turret with its saddle slides
directly on bed-ways enabling
longer work to be machined

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Types of Lathe …
6. Special purpose lathes
 Used for special purposes
 Wheel lathe: For finishing journals, turning locomotive wheels
 Gap-bed lathe: A section of bed adjacent to tailstock is
removable thereby allowing very large diameter work to swing
 Duplicating lathe: To duplicate the shape of a template on to a
workpiece
Wheel lathe Duplicating lathe
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Types of Lathe …
7. Automatic lathe
 Automatic control: Once the tools are
set and the machine starts, all the
operations will be performed
automatically
 Change of tools, speeds and feeds are
done automatically
 The jobs are made continuously one
after the other without the intervention of
operation
 High speed, Heavy duty and Mass
production lathe
 Single or multi spindle
 Capable of simultaneous cuts
Operator’s role:
 Loading the bar stock
 Setting the tools
 Machine maintenance

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Machine Tools 17
Types of Lathe …
7. CNC lathe
 Computer Numerical Control
 Wide variety of process capability
 Multiple axes
 Indexing and contouring head
 On-line and off-line programming available
 Equipped with one or more turrets
 Each turret is equipped with a variety of tools
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The Bed
• Rigid to withstand the
cutting forces
• Massive, sufficient to
absorb vibration
• Resist the torsional
stresses set up.
• Should be seasoned
naturally to avoid
distortion.
Diagonal ribs
Lathe

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The Headstock
• Headstock spindle
• Cone Pulley
• Backgears and backgear lever
• Gear Box
• Live center
Main of parts of headstock are:
Lathe
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The Headstock Spindle
1. Threaded end
2. Taper sleeve
3. Live center
4. Threaded nose
5. Spindle hole
Lathe

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The Headstock
• Need for speed change
–Workpiece material
–Cutting tool material
–Type of operation
–Workpiece size
–Surface finish
–Cutting fluid
–Rigidity of machine tool
Lathe
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Methods to vary the speeds
1. By belt drive on cone pulley fitted
on the headstock spindle with or
without a back gear arrangement.
2. By all gear drive using sliding
gears or clutches.
3. By variable speed motor.
Lathe

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Belt Driven Backgeared Headstock
In a belt driven back geared
headstock, multiple speeds can
be obtained
1. Direct speed or back gear out
2. Indirect speed or back gear in
Spindle Cone Pulley
Countershaft Cone
Pulley
Lathe
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Speed Ratios
• Direct speeds:
Spindle speed =
• Indirect speeds:
Spindle speed =

Back gear ratio =

Lathe

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Geared Headstock
15 – splined headstock spindle.
Fig.9speedall-gearedheadstock
Speed distribution, r (GP Ratio)

1 – Fast Pulley
2 – Loose pulley
3 – Spindle shaft
4 to 13 – gears with
Z4 to Z13 teeth
10 – Intermediate shaft
14 – Gear box casting
Preferred values for ‘r’,
= 1.12, 1.25, 1.4, 1.6 and 2
Lathe
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Tailstock
Lathe

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Carriage
Lathe
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Single Screw Tool post
5 – concave
ring
Fig.: Single screw tool post
1 – screw
2 – body
3 – tool
4 – convex
rocker
Lathe

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Four way Tool post
Figure: Four way Tool post
1 – clamping
handle
2 – central
locking
bolt
3 – set
screws
4 – tool
Lathe
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Feed Mechanism
• Feed:
The distance advanced by the tool into or along
the workpiece for each revolution of the work.
 Units: mm/rev. or mm/min.
• Types
– Longitudinal feed (cylindrical turning, thread
cutting, etc.)
– Cross feed (facing, parting, etc.)
– Angular feed (taper turning, chamfering, etc.)
Lathe

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PowerTrain
End of bed gearing
Changegear
train
Feedrod&
leadscrew
Apron
Mechanism
Tumbler gear
feed reverse
mechanism
Bevel gear
feed reverse
mechanism
Feed gear box
1. Sliding gear
mechanism
2. Sliding
clutch
mechanism
3. Gear
cone and
Norton feed
gear
4. Sliding
key
mechanism
5. Combination
of two or more
of 1, 2, 3, 4
Feed Mechanism
Lathe
Clutch handle
Figure: Layout diagram of feed drive
Tumbler gear
Change Gears
Norton Gears
Sliding Key Mechanism
Feed Mechanisms …
Headstock spindle
Sliding key
operating handle
Lead screw
Feed rod

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Feed Reverse Mechanism
using Tumbler Gears
Tumbler gears are used to give the desired direction of movement to the
lathe carriage, via lead screw or feed rod.
Tumbler Gear Mechanism
Tumbler Gears
Forward motion: A-B-D: Carriage moves towards headstock
Reverse motion: A-C-B-D: Carriage moves away from headstock
Drawback: Non-rigid construction, hence not suitable for heavy duty
Two pinions B and C
are mounted on a
bracket.

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Feed Reverse Mechanism
using Bevel Gear Mechanism
Constructional details
1 – headstock spindle
2 – spindle gear
3 – driver gear keyed to stud shaft (7)
5 – gear on the lead screw (6)
8, 10, 12 – bevel gears with equal no. of teeth
11 – clutch (keyed to stud 7 by a feather key)
9 – lever (to engage clutch to gear 8 or 10 or
keep in neutral position)
(Gear 13-sleeve-bevel gear 8) rotate freely on
stud 7 as one unit
bevel gear 10 also rotates freely on stud 7
The clutch operated bevel gear feed reversing mechanism incorporated below the
headstock or in the apron provides sufficient rigidity in construction.
Operation:
When clutch is engaged to bevel gear 8:
Motion flow: gear 2 – Idler gear – (gear
13, sleeve, bevel gear 8) – (stud 7, gear 3)
Result: Gear 3 rotates in the same
direction as that of gear 2. Hence,
Forward motion, Carriage moves towards
headstock.
When clutch is engage to gear 10:
Motion flow: gear 2 – Idler – (gear 13,
sleeve, bevel gear 8) – bevel gear 12 –
bevel gear 10 – (stud 7, gear 3)
Result: Gear 3 rotates in opposite direction
to that of gear 2. Hence,
Reverse motion, Carriage moves away
from headstock.
Feed Reverse Mechanism …
using Bevel Gear Mechanism

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Feed Mechanisms …
Change Gears
Change gears are used in
thread cutting to give
proper relative motion
between the work and tool
Change Gear Mechanism
Figure: Change gears
Change Gears
E
G

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Feed Mechanisms …
Norton Feed Gears
Norton Feed Gears

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Feed Mechanisms …
I – driving shaft;
II – driven shaft
1 – sliding key operating handle
2 – sliding rod
3 – lever spring
3
I
II
 It consists of a cone of gears
mounted on a hollow shaft.
 Gears rotate independently freely on the
shaft.
 Steel washers are placed between the
gears to prevent simultaneous
engagement of adjacent gears.
 With the help of sliding key (that
slides within the hollow shaft), any one of
the gears may be engaged to the cone
gears on the driven shaft.
 Motion is then transmitted finally to the
lead screw or feed rod.

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Apron Mechanism
1 – lead screw; 2- feed rod
3 – half-nut; 4 – cross feed screw
5, 6, 7 – Gear train for cross feed
9 – cone clutch for longitudinal feed
10, 11 – gear train for long. feed.
12 – gear for hand wheel
13 – pinion; 14 – apron
15 – rack; 16 – hand wheel
17 – knob for longitudinal feed
18 – cone clutch for cross feed
19 – knob for cross feed
20 – lever; 21 – cam
22 – sliding gear
23 – gear on worm shaft
24 – worm; 25 – cam plate
26 – half nut operating handle
Apron Mechanism

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Feed Rod & Lead Screw
lead screw
feed rod
Feed rod
Used to engage automatic tool feed during turning,
boring, facing etc.
Automatic tool feed is obtained by engaging feed rod so
as to transmit power from the lathe spindle to the apron
gears
Lead screw: Long threaded master screw
Engaged during thread cutting operation
In lathes without feed rod, lead screw may be used for turning, boring etc.
Split Half Nut
Mechanism
1 – cam slot; 2 – frame; 3 – lead screw;
4 – hand lever; 5 – pin; 6 – circular plate;
7 – half nuts
Fig. b) Sectional views of Half Nut Mechanism
 Half Nut is engaged to the lead
screw during threading.
 The nut is made in two halves.
 Each of these halves carries a pin at
the back (P1 and P2 as shown in
Fig. a) which engages into the cam
slots provided in a plate at their back.
 When this plate is rotated by
means of the lever L, it engages or
disengages the split half nut with the
lead screw depending upon the
direction of rotation of the lever.
Fig. a) Half nut

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Machine Tools 47
Kinematic Structure of a Lathe
Lathe
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Specifications of a Lathe
A = Length between centers
B = Swing over gap (Gap bed lathes)
C = Height of centers
D = Swing over carriage
E = Swing over bed

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Turning Operation
FIGURE : Schematic illustration of a turning operation
showing depth of cut, d, and feed, f. cutting speed is the
surface speed of the workpiece at the tool tip.
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Lathe Operations
Fig: Various cutting operations that can be performed on a
lathe.

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Lathe Operations
Fig: Various cutting operations that can be performed on a lathe.
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Accessories&Attachments
Lathe – Accessories & Attachments
Accessories
Devices employed for holding
and supporting the work and the
tool.
Attachments
Devices to increase production
and efficiency and widen its scope
of use.

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Lathe – Accessories & Attachments
Accessories
Centers
Face & Angle Plates
Dogs or Carriers
Chucks
Mandrels
Rests
Attachments
Bar Stops
Thread Chasing Dials
Taper turning
Milling
Grinding
Gear Cutting
Hydro-copying
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Centers
A – Ordinary Center E – Tipped (brazed) Center
B – Ball Center
F – Insert type Center
D – Half Center
H – Use of half center
1 – Half center
2 – Facing tool
G - Pipe Center
C – Frictionless Center
1 – Insert type center
2 – Nut
3 – Roller bearing
4 – Thrust bearing
5 - Housing

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Driving Plates and Dogs
Fig: Eccentric Turning
Fig. Straight dog
Boss Threaded Hole
Projected Pin
Fig: Driving Plate
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Holding the work between Centers
Fig.: mounting the work between centers using a "dog”

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Chuck
Fig: Four Jaw Chuck
1- concentric circle; 2 – chuck body;
3 – Jaw screw; 4 – jaw; 5 – gripping
surface; 6 – recess for back plate.
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Chuck
Fig: Three Jaw Chuck

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Chuck
Fig: Magnetic Chuck
1-work; 2-magnetic material; 3-keepers;
4-face plates, 5-magnet
Fig: Hydraulic Chuck
1-cylinder; 2-air passage; 3-head stock spindle; 4-piston;
5-valves;; 6-piston rod; 7-link; 8-jaw; 9-guide; 10-sliding unit
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Collet
1-Bearing; 2-Spindle; 3-Nut;
4-Key; 5-Chuck; 6-Collet
Fig: Collet Chuck

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Collet
Fig.: collet
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Face Plate & Angle Plate
Clamping
Plate
Balance
Weight
Packing Work
Fig: Face Plate
Fig: Angle Plate
1-face plate; 2-balance weight; 3-elbow pipe;
4-clamping nut; 5-angle plate; 6-clamping nut

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Face Plate
Fig.: face plate for non-cylindrical workparts
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Mandrels
Plain Mandrel
Step Mandrel Threaded Mandrel
Collar Mandrel

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Mandrels
Fig: Cone Mandrel
1-solid cone; 2-sliding cone; 3-nut
Fig: Gang Mandrel
1-fixed collar; 2-hollow workpieces;
3-movable collar; 4-nut
Fig: Expansion Mandrel
1-sleeve; 2-tapered pin
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Steady Rest

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Follower Rest
Fig.: Follower rest
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Thread Cutting - Terminology
Fig. Elements of external threads

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Thread Cutting - Terminology
Fig. Single Start Fig. Double Start
Fig. Triple Start
.
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Thread Cutting
Fig: General set-up of lathe for screw cutting

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Thread Cutting - Change Gear Ratio

,

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Cutting metric thread on
British standard lead screws or Vice Versa
To cut metric threads on lathes having
British standard lead screw:
To cut British standard threads to be cut on
a lathe having lead screw of metric pitch:
5
127

127
5


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Cutting R.H. and L.H. Threads
Right Hand threads:
 Threads slope up to the right when
screw is held vertically.
 The spindle and the lead screw will
rotate in the same direction.
Left Hand threads:
 Threads slope up to the left when
screw is held vertically.
 The spindle and the lead screw will
rotate in opposite direction.
This change of direction of rotation on
lathe is effected by tumbler gear or by
using proper number of idlers.
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Thread Cutting - Gear Trains
Simple gear train Compound gear train
 Often lathes are equipped with a set of gears
ranging from 20T to 120T in steps of 5T.
 In addition, a gear of 127 teeth is also
provided which is known as translating gear.

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Left Hand thread - Applications
Where the rotation of a shaft would cause a
conventional right-handed nut to loosen rather
than to tighten, e.g. on a left-hand bicycle
pedal.
In combination with right-handed threads in
turnbuckles.
In Gold ornaments, e.g. ear studs.
In some gas supply connections to prevent
dangerous misconnections, for example in gas
welding the flammable gas supply uses left-
handed threads.
RH ThreaLH Thread
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Examples:

2
6

1
3

1
3

20
20

20
60
Simple train with one idlerSimple train with one idler

1
3

25
25

25
75

1
3

30
30
30
90
Calculate change gears for cutting R.H.
threads of 2 mm pitch on a lathe having
lead screw of 6 mm pitch.
Pb.:
Soln:

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Examples:
Calculate change gears for cutting L.H.
threads of 1.5 mm pitch on a lathe having
Pb.:
Soln:

1.5
6
1
4

1
4

20
20

20
80

1
4

25
25

20
100
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Examples:
Calculate change gears for cutting R.H.B.S.W.
“V” threads of 12 TPI on a lathe having lead
screw of 8 TPI.

1 12⁄
1 8⁄

2
3

20
20

20
60

2
3

25
25
25
75
8
12
2
3
Pb.:
Soln:

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Machine Tools 79
Examples:
Calculate change gears for cutting R.H.
threads of 1 mm pitch on a lathe having

1
8

1
8

20
20

20
160
Compound Gear train with no idler
Gear A = 20 Gear B = 80
Gear C=30 Gear D = 60
Gear C=30 Gear D = 60

1
8
1
4 2
1
4
1
2
1
4
20
20
1
2
30
30

20
80
30
60
Pb.:
Soln:
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Examples:
Calculate change gears to cut R.H. threads
of 25 TPI on a lathe having lead screw of 6
TPI.
Pb.:
Soln:

6
25

6
25
2 3
5 5
2
5
20
20
3
5
15
15

40
100
45
75
Gear C = 45 Gear D = 75

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Examples:
Calculate change gears to cut L.H. single
start threads of 0.25” pitch on a lathe having
lead screw of 8 mm lead.
Compound Gear train with one idler
Compound Gear train with one idler
0.25"
1
4

127
5
1 4⁄
8
127
5 32
127
5 16 2
⇒
127
80
1 50
2 50
127 50
80 100
Pb.:
Soln:
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Setting of Tools for Threading
Fig. Setting threading tool
for external threading
Fig. Setting threading tool
for internal threading

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Feeding the Tool in Threading
Fig: Straight Thread
Fig: Inclined feed
Fig: Inclined feed using a form tool
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Fig.: Cutting a screw thread on a lathe
Inset shows face of threading dial
Thread Cutting

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Providing undercut
Fig.: Under Cut
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Cutting Square and Acme Threads
Fig. Tool setting for square
threads
nceCircumfere
threadofLead ..
tan 

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Fig.: Threading cycle to produce threads
Thread Cutting Cycle
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Thread Chasing Dial
Fig: Thread Chasing Dial

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Taper Turning

1
100
1 100
tan
2⁄

2
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Tail Stock Set-over Method
Let,
H = set-over required
D = larger diameter
d = smaller diameter
L = total length of work
l = length of taper
(all dimensions in ‘mm’)
sin
α is very small and hence, sin tan
tan
2
But, ∴
2

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Swiveling the Compound Rest
Fig. Turning taper by swiveling the compound rest
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Taper turning attachment
Fig. Use of taper turning attachment

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Form or Broad Nose Tool
Fig. Turning short taper by a form (broad nose) tool
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Machining Time Calculations in Turning
Cutting speed:
where d = diameter of the work in mm;
N = speed of the work in rpm.
Feed: mm / rev. or mm / min.
f (mm / min) = f (mm / rev) X N (rev / min)
Machining time:
where l = length of the job, mm
f = feed in mm/rev.;
N = speed in rpm.

1000
/


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Machine Tools 95
References
TextBooks • Materials and Processes in Manufacturing,
by E. Paul DeGarmo, et al, Wiley
• Manufacturing Engineering and Technology,
by S Kalpakjian and Steven R Schmid, Pearson
• Machining Technology – Machine Tools and
Operations, by Helmi A Youssef and Hassan
El-Hofy, CRC Press
• Manufacturing Science, by A Ghosh and AK
Mallik, EWP
• Machining & Machine Tools, by AB
Chattopadhyay, Wiley

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Lathe-Types, Parts, Feed Mechanisms, Specifications,Lathe Accessories and Attachments,Lathe Operations