Transcript Taper Turning - EngineeringDuniya.com

LATHE OPERATIONS
The various operations that can be performed on a lathe
are:
1.
2.
3.
4.
5.
6.
7.
8.
Turning.
Step turning.
Taper turning.
Thread cutting.
Facing.
Knurling
Chamfering.
Parting off
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Plain turning operation.
Work piece held by
chuck
Cutting
speed
Workpiece
Depth of cut (d)
Machined
surface
N
Chuck
Feed
Tool
Chip
Depth of cut
Plain Turning:
• The process of metal removal from the cylindrical jobs is called straight
or plain turning.
• Cross slide and the carriage are used to perform turning operations.
• Plain turning operation is performed in two steps.
– Rough turning (Roughing)
– Finish turning (Finishing
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Turning
• It is a process of removing excess material from the work
piece to generate cone-shaped or cylindrical surface.
• Types:
– Straight turning
– Shoulder turning
• Shoulder turning (Step turning)
– Job having different diameters, so it forms the step from
one diameter to other.
Facing
•
•
•
•
Tool is fed in a direction perpendicular to the lathe axis
Lateral/transverse surface of job is machined.
Length of tool travel = half the dia. of job
Depth of cut is along the axis of job
Parting off
Also know as cutting off operation, Useful in
away the required length from the bar stock.
Tool used is parting off tool (HSS)
Job is held in chuck &
rotated at relatively high speed
cutting
Tool is fed in a direction normal to axis of rotation of job.
High feed rate is given
Abundant supply of coolant should be used
Knurling
Process of embossing a diamond/ straight shaped pattern
onto job.
Types: Straight , diamond & diagonal.
Indentations (knurl) provided on many outside surfaces of
measuring instruments, tool etc for better grip
Special tool (knurling tool) is used for operation.
Tool consists of straight shank fitted with 1 or 2 knurling
wheels (hardened steel & contains teeth on its outer surface)
at its front.
Job is held in chuck and tool is fed across axis of job pressing
against its surface.
In operation, tool should not be withdrawn till its complete.
2-3 passes are required & speed should be low.
Chamfering
Process of beveling the extreme sharp end of job.
Provided - to make the edge blunt
- to enable free movement of nut on threaded job
- to remove burrs
Thread cutting
It is operation of producing helical grooves of specific
shapes on cylindrical surface.
Job is held between centers/chuck/face plate & tool is held
in tool post.
To produce threads of pitch, P mm, the tool must travel a
distance equal to P and also job must make one complete
rotation.
There must be definite rotary & linear motion between job &
tool.
This is achieved by locking/engaging the carriage with lead
screw through a split half nut mechanism and gear ratio
between head stock spindle and lead screw.
Motion is transmitted from spindle to lead screw.
Taper Turning
• Taper: Defined as a uniform increase or decrease
in diameter of a piece of work measured along its
length.
• Taper Turning: To produce a conical surface by
gradual reduction in diameter from a cylindrical
work-piece.
• Methods:
–
–
–
–
–
A broad nose form tool
Setting over a tail stock centre
Swiveling the compound rest
Taper Turning attachment
Combining longitudinal & cross feed
Taper Elements
Total Taper = D – d
Taper = (D – d)/L
Taper Angle (α) [Half taper angle]
Amount of taper (Conicity -K): Ratio of difference in diameter of
taper to its length, K = D- d / L
From, triangle – ABP or AEF, [AF = ½ of total taper & EF = L]
(taper gradient) tan α = AF/EF = D-d/2L
A broad nose form tool
Method is suitable only for
very short tapers (max.
20mm length)
Form or broad-nose tool is
used [cutting edge is ground
to contain half taper angle]
During operation, lot of
vibrations are caused as full
cutting edge is involved in
cutting
Swiveling the Compound Tool Rest :
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• In this method the job is rotated coaxial with lathe axis,
• Compound rest is swiveled to the required taper angle and
locked in position.
• The carriage is also locked at that position.
• To assist in swiveling at particular angle, the base of the
compound rest is graduated in degrees.
• For taper turning , the compound tool rest is moved linearly
at an angle so that the cutting tool produces the tapered
surface on the workpiece.
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• Limited to short tapered lengths.
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Taper angle: Angle at which the compound rest to be
rotated is calculated as below.
tan α =
Dd
2L
α = half taper angle
D = larger diameter of the taper
d = smaller diameter of the taper in mm.
L = length of the taper
Dd
Taper or conicity (k) =
L
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Taper turning by Tailstock set over method
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Setting over a tail stock centre
Principle of this method: To shift the axis of rotation of the
work piece at an angle to lathe axis & feeding tool parallel to
lathe axis
Method is suitable only for smaller taper angle on longer jobs
Angle at which axis of rotation of work piece is equal to half
taper angle
This is obtained by sliding body of tail stock towards or away
from operator by a set over screw
Amount of set over is limited and centers are not equally
stressed
Required amount of set over can be calculated as follows:
.
Amount of off-set =
(D  d )L
2l
Where D= larger diameter, d= smaller diameter
L= length of work,
l= length of taper.
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specification of a lathe.
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Specification of a lathe
1. Distance between centers:
– Maximum distance that can be obtained between
the lathe centers
– Represents the maximum length of the work piece
that can be held between centers.
2. Overall length of the bed:
– Maximum length of the bed starting from the head
stock end to tailstock end.
3. Swing diameter over the bed:
– Largest diameter of the work piece that can be
rotated without touching the bed.
4. Swing diameter over a gap in the bed:
– Maximum diameter and the width of a work piece
that can be mounted between the centers.
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Lathe classification
• Bench Lathe
• Speed Lathe
• Engine Lathe
• Tool room lathe
• Capstan and Turret Lathe
• CNC Lathe (automatic lathe)
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