WEEK THREE
MACHINING
Technician, Mr Koech Raymond
Introduction
Lathe is a machine that is used to create a piece which has a symmetry about an axis of rotation.
Lathe machine accessories
Face plate
Chuck (4-jaw chuck)
Self centered chucker (3-jaw chucker)
Steady rest center
Follower steady rest
Life center
Dead center
Main parts of a lathe machine
1. Bed
2. Head stock
3. Tail stock
4. Carriage assembly
Bed
The bed of the lathe forms the base of the machine. It is supported on two legs at a convenient
height. It carries the head stock and the tail stock for supporting the work and provides a base for
the movement of the carriage assembly which carries the tool
Head stock
The head stock houses the spindle and the means for supporting and rotating the spindle
Tail stock
The tail stock is for the purpose of primarily giving an outer bearing, support for work being
turned on centers. It can be adjusted for alignment or non-alignment with respect to the spindle
center and carries a center called dead center for supporting one end of the work. Both live and
dead centers have 60 conical points to fit center holes in the work, the other end tapering to allow
for good fitting into the spindles.
Carriage Assembly
The carriage assembly of the lathe comprises of a number of components which support,
move and control the tool. The carriage assembly consists of a saddle, cross slide,
compound rest, top slide, tool post and apron.
Lathe machine operations
Turning
Straight turning
Step turning
Facing
Facing is an operation used to produce a flat surface at right angles to the
rotational axis of the work piece.
Taper turning
Process of turning at an angle and a given distance
Drilling
Process of making a hole by the aid of a drill bit
Boring
Boring is the process of enlarging a hole produced by drilling, casting, punching
or forging with the help of a single point tool
Parting
Is the process of cutting of a work piece into two
Chamfering
Is the process of removing sharp edges from a work piece to prevent cuts
Center drilling
Making a small hole at the end of a work piece for holding by the life or dead centers
Knurling
Knurling is the process of embossing a diamond shaped pattern on the cylindrical
surface of a work pie is done on the work piece so that it does not slip when held
and operated by hand.
Threading
External threading
Internal threading
Minor operations
Contour turning
Form turning
Discussion
Vernier calipers is used for measurements done
One should know how to use it properly
Always withdrawal the tool before turning off the lathe machine
One person should operate lathe machine at a time
Task one
Sharpening of tools
Bench grinder is used in sharpening of tools
Thread cutting tool
Turning, taper turning tool, turning tool
Task two
Internal and externa thread making
Procedure
I. Part off a work piece of diameter 38mm by 125 long
II. Mount the work piece in the lathe machine and tighten using chuck key
III. Set the machine at moderate speed
Operations done the work piece
The operations are done from larger diameter to a small diameter
Facing
Straight turning , diameter 36 mm by 125 mm long
Step turning , 55 mm
Taper turning, 45 degrees for 4 mm
Straight turning , diameter 25 mm, by 25 mm long
Taper tuning, 45 degrees by 4 mm long
Straight turning , diameter 16 mm by 30 mm long
External thread cutting, M16*2
Drilling , diameter 16 mm by 40 mm long
Internal thread cutting, M16*2
Chamfering both ends
Task three
Hinge making
Procedure 1
I. Part of a work piece of diameter 38 mm by 85 mm long
II. Mount the work piece on lathe machine and tighten by chuck
key
III. Set the machine at moderate speed
operations done on the work piece
Facing
external step turning
Step turning (1), diameter 30 mm by 40 mm long
Facing
Step turning (2), diameter 20 mm by 20 mm long
Facing to obtain a work piece of 80 mm long
Chamfering both ends
Procedure 2
I. Cut off a work piece of diameter 38 mm by 45 mm
long
II. Mount it and tighten
Operations done
Facing
Center drilling
Drilling, diameter 20 mm by 45 mm long
Boring
Diameter 30 mm by 20 mm long to
obtain internal step turning
Facing to obtain 40 mm long
Chamfering done on one end
Task four
Setting of a long work piece
Done when a 4-jaw chucker is used for holding
Dial gauge , block gauge, steady rest and unsteady rest are used for setting
Done to prevent vibrations which may be caused by a long work piece
Procedure
I. Mount a long work piece on a 4-jaw chucker
II. Set the machine at moderate speed
III. Set the block gauge pointer near the work piece, note the distane
IV. The distance between the work piece and the pointer should be uniform when the machine
rotates
V. For a dial gauge, the pointer should be at a steady position when the machine rotates
VI. Steady and unsteady rests are for holing the work piece
using steady rest
using block gauge
using dial gauge
Nut and bolt
Procedure
I. Part off a work piece of diameter 25 mm by 255 long
II. Mount the work piece in the lathe machine and tighten using chuck key
III. Set the machine at moderate speed
Operations done the work piece
Bolt
a. Facing one end
b. Knurling diameter 22 mm by 200 mm long
c. External thread cutting of M22 by 2.5, 200 mm long
d. Grooving , diameter 18 mm by 10 mm long at the edge
e. Another grooving of 18 mm by 10 mm after the threads
f. Facing to make the bolt 250 mm long
g. Drilling, diameter 8 mm for the handle
h. Welding the handle
Nut
a. Part a work piece of diameter 38 mm by 43 mm long
b. Face the ends to make it 40 mm long
c. Drilling, diameter 19.5mm
d. Internal thread cutting ,M22 by 2.5
e. Chamfering the ends of the nut
f.
Recommendations.
1. The school should make an effort of increasing the lathe machines in the
workshop to ensure that all students are able to assess and interact with the
machine for a longer period to ensure they learn more.
2. Students need to make sure they cooperate and all participate in the practice to
learn more.
References
machining fundamentals by John R Walker , 1969
Machining and CNC technology by Michael Fitzpatrick , 2018
Basic lathework for home mechanist by Stan Bray , 2013
