2. 2
Intended Learning Outcomes
• List the main components of a lathe
• Understand the functions of different components
• Describe the workpiece holding methods
• Describe the tool holding methods
• Describe the different mechanical mechanisms in center lathe
• Understand the main specifications of a Lathe
4. 4
Lathe
• Lathes are generally considered to be the oldest
machine tools still used in industry.
• One-third of machine tools operating in engineering
plants are lathe machines.
• Lathes are used in both job and mass production.
• Lathes are employed for various operations.
• Also known as the “Mother of All Machine Tools.”
9. 9
Head Stock
• Headstocks are the main body parts that are placed on the left side of the bed.
• It serves as a holding device for gear chains, spindles, driving pulleys, etc.
• The mechanism of the headstock is driven by an electric motor that rotates the
spindle. It is made of cast iron.
10. 10
Head Stock
Accessories mounted on headstock spindle:
1.Three jaw chuck
2.Four jaw chuck
3.Collect chuck
4.Mandrel
5.Lathe center and lathe dog
6.Faceplate
MACHINING PROCESSES, LECTURE 2 10
11. 11
Chucks
• The three-jaw chucks are used to clamp circular and hexagonal
rods, whereas the independent four-jaw chucks are especially
useful in clamping irregular workpieces.
12. 12
Collets
• Generally, collets are used on smaller work pieces than
typical three-jaw chucks. The general range for collets are
1/16in to 2.5in
13. 13
Mandrels
Mandrels (1) are used to hold WPs with previously machined holes.
The WP to be machined (2) is tightly fitted on a conical mandrel,
tapered at 0.001, and provided with center holes to be clamped
between centers.
14. 14
Between two centres
• Holding the WP between centers is a more
accurate method for clamping a long WP
which is rotating at high speed.
15. 15
Faceplate
• Large WPs cannot be clamped in chucks and are therefore mounted
on a faceplate or on a plate fixture that is attached to face plate.
19. Bed
• The bed is the foundation and
backbone of a lathe.
• Its rigidity and alignment
affect the accuracy of the
parts machined on it.
• Therefore, lathe beds are
constructed to withstand
the stresses created by heavy
machining cuts.
• On top of the bed are the
guideways, which usually
consist of two inverted vees
and two flat bearing surfaces.
20. 20
Tail Stock
Tail Stock is situated on the right side above the lathe bed.
1.Holding long workpiece.
2.Holding the tool for drilling, reaming, tapping, etc.
21. 21
Tailstock
A morse taper is a standard system for fitting drill chucks and other
attachments, to the spindle of lathe tailstocks.
24. Carriage
• It is located between headstock and tailstock.
• It is used to hold and move the tool post along the bed either
towards or away from the headstock.
• It slides on the guideways.
• It is also made of cast iron
• It has six main parts:
• Tool Post
• Compound slide
• Compound Rest
• Cross slide
• Saddle
• Apron
26. Carriage: Compound Slide
• Compound slide is a T -shaped rounded slot, which is fixed
with cross slide upper surface by two bolts, which is related to
a micrometer sleeve and screw handle with the outer edge of
screw.
• The automatic feed
is not possible in compound slide.
27. Carriage: Compound Rest
• It is a part which connects to cross slide and compound slide.
• It is mounted on the cross slide by tongue and groove joint.
• The compound rest can be swiveled to the required angle while turning tapers.
• A top slide known as compound slide is attached to the compound rest by dovetail joint.
29. Carriage: Cross Slide
• The cross slide is a component found on the top of a lathe that allows the
tool bit to slide back and forth.
• The cross slide is moved by the feed screw.
36. 36
Feed rod and lead screw
• Feed rod is used to move the carriage and it is used in most turning
operations.
• Lead Screw is used for thread cutting operation in a lathe machine
tool using the half nut in apron mechanism.
37. Apron Mechanism
• The front portion of a carriage call as apron. It consists of all control keys.
• The handle operates the carriage. It has a housing, which has a set of gears and split nut.
• Automatic feed and threading control are on the apron.
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38. Apron Mechanism
• A worm is mounted on the feed rod by a sliding key. The worm meshes with
a worm gear on whose axis another gear G1 is attached.
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40. Apron Mechanism
• Gear G1 is attached to a small gear G2 by a bracket as shown in the diagram. Gear
G4 is positioned to be in mesh with the rack gear always. Another gear G3 is
mounted on the same axis of gear G4.
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41. Apron Mechanism
• The carriage hand wheel meant for longitudinal feed is attached to the gear G5 on
the same axis. The gears G3 and G5 are always in mesh. The gear G6 is attached to
the cross-slide screw.
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42. Apron Mechanism
• The feed selection lever can be kept in neutral, up and down positions to obtain the
following movements.
1. Hand feed and power feed to the carriage
2. Hand feed and power feed to the cross slide
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43. Apron Mechanism
Hand feed to the carriage
• Feed selection lever is kept in neutral position and the carriage hand wheel is rotated.
The gear G4 attached to the rack gets rotation through the gears G5 and G3. The carriage
moves longitudinally.
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45. Apron Mechanism
Power feed to the carriage
• When feed selection lever is kept in up position (U), the gear G2 will mesh with gear G3.
Gear G4 gets rotation through gear G3 and the carriage gets automatic (power) feed.
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46. Apron Mechanism
Hand feed to the cross slide
• Feed selection lever is kept in neutral position. The cross slide will move on rotation of
the cross-slide hand wheel.
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47. Apron Mechanism
Power feed to the cross slide
• When the feed selection lever is kept in down position (D), gear G2 will be in contact
with gear G6. The rotation of G6 will make the cross slide screw also to rotate and the
cross-slide moves automatically.
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48. Apron Mechanism
Power feed to the carriage for thread cutting
• When the two half nuts in the apron are made as one unit, lead screw makes the
carriage to move automatically and cut threads of required pitch value. The mechanism
is designed that when the half‐nut is engaged with the lead‐screw, the automatic feed
motion from the feed‐rod is disconnected
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