MECHANICAL ENGINEERING
SCIENCE (UE23ME131A)
Srinivasa Prasad K S
Department of Mechanical Engineering
MECHANICAL ENGINEERING SCIENCE
Unit4
Srinivasa Prasad K S
Department of Mechanical Engineering
MECHANICAL ENGINEERING SCIENCE
Chapter 1 – Machining Processes
Srinivasa Prasad K S
Department of Mechanical Engineering
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
OPERATIONS ON LATHE
TAPER TURNING
Offsetting the tailstock –
Still another method sometimes used is the method of offsetting the tailstock
from the centre position.
By offsetting the tailstock, the axis of rotation of the job is inclined by the half
angle of taper as shown in Figure.
The feed to the tool is given in the normal manner parallel to the guideways.
Thus the conical surface is generated. The offset that is possible is generally
limited, and as such this method is suitable for small tapers over a long length.
The disadvantage is that the centres are not properly bearing in the centre holes
and as such there would be non-uniform wearing taking place.
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
OPERATIONS ON LATHE
TAPER TURNING
Taper turning attachment method –
Still another method for turning tapers over a comprehensive range is the use
of taper turning attachment.
In this method a separate slideway is arranged at the rear of the cross slide.
This slide can be rotated at any angle to be setup. The block that can slide in
this taper slide way is rigidly connected to the cross slide.
As the carriage moves for feeding, the block moves in the inclined track of
the slide, it gets the proportional cross movement perpendicular to the feed
direction, the cross slide and in turn the cutting tool gets the proportional
movement. Thus the tool tip follows the taper direction set in the attachment.
This method is most commonly used for a range of tapers.
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
OPERATIONS ON LATHE
KNURLING
Knurling is a metal working operation done in a lathe.
In this a knurling tool having the requisite serrations is forced on to the
work piece material, thus deforming the top layers. This forms a top
surface, which is rough and provides a proper gripping surface.
PARTING
Parting and grooving are similar operations. In this a flat nosed tool
would plunge cut the work piece with a feed in the direction
perpendicular to the axis of revolution. This operation is generally
carried out for cutting off the part from the parent material.
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
WORK HOLDING DEVICE
The most common form of work holding device used in a lathe is the chuck.
Chucks come in various forms with a varying number of jaws. Of these the
three jaw chuck or the self-centering chuck is the most common one.
The main advantage of this chuck is the quick way in which the typical round
job is centred. All the three jaws move radially inward or outward by the same
amount.
Thus, the jaws will be able to centre any job, whose external locating surface
is cylindrical or symmetrical, like hexagonal.
The independent jaw chuck has four jaws, which can be moved in their slots
independent of each other, thus clamping any type of configuration. Since
each of these jaws could move independently any irregular surface could be
effectively centred.
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
LATHE SPECIFICATIONS
In order to specify a lathe, a number of parameters could be used based on the
specific application. The following are the basic elements generally specified
for the capability of the lathe machine.
● Distance between centres (L) —this specifies the maximum length of the job
that can be turned in the lathe.
● Swing over the bed (H) —this specifies the maximum diameter of the job (A)
that can be turned in the lathe machine, generally restricted to small length jobs.
● Swing over the cross slide (H-h) —this specifies the maximum diameter of the
job (B) that can be turned in the lathe machine with the job across the cross slide,
which is generally the case.
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
TYPES OF LATHE
BENCH LATHE
The name bench lathe is given to a small centre lathe that is
mounted on a workbench.
In design it has the same features as centre lathes and differs
only in size and mounting.
It is adapted to small work, having a maximum swing
capacity of 255mm (10’’). Bench lathe is used for small
precision work like instrument parts.
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
TYPES OF LATHE
CAPSTAN AND TURRET LATHE
The main characteristic feature of the capstan and turret lathes is the six sided
(hexagonal) block mounted on one end of the bed replacing the normal tailstock. This
allows for mounting six tool blocks each of which can contain one or more tools
depending upon the requirement.
Further on the cross slide, two tool posts are mounted, one in the front and the other in
the rear. Each one of them can hold up to four tools each. Thus, the total carrying
capacity is a maximum of 14 tools when only one tool is mounted in each of the
locations.
The turret is mounted on a saddle, which in turn is sliding on the bed. When the saddle
moves on the bed during the return stroke it would automatically be indexed to the
next tool position, thus reducing the idle time of the machine.
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
TYPES OF LATHE
CAPSTAN AND TURRET LATHE
CAPSTAN LATHE
TURRET LATHE
MECHANICAL ENGINEERING SCIENCE
MACHINING PROCESSES
TYPES OF LATHE
GAP LATHE
It is used for machining large work with irregular protrusions. On this lathe, a section
of bed, adjacent to the headstock can be removed to machine a large size workpiece.
