National Institute of Technology

Hamirpur

UNIT 3
MACHINING OPERATIONS AND
STUDY OF LATHE MACHINE

Dr. P. K. Sood
Associate Professor
MACHINIING
Machining is the process of
cutting, shaping, or removing
material from a work-piece using
a machine tool.
 Various Machining Operations
• Machining operations are
classified into 3 principle
processes and they are
Turning, Drilling And
Milling.

• There are other operations

too that fall in
miscellaneous categories
such as Boring, Sawing,
Shaping, And Broaching. A
specific machine tool is
required for taking care of
each machining operation.
 TURNING
• Turning is basically a lathe
operation by which the metal is
removed from the work piece
outside its diameter using a
cutting tool. This operation is
performed on a lathe which is a
machine where the work piece is
adjusted and the tool is kept
stationary whereas the
workspace is rotated.
• Lathes are specially designed for
the turning operation and they
help in cutting the metal in the
most precise way.
• The work piece is placed on the
chuck and the machine rotates
the stationary tool to cut the
unwanted parts from the piece.
 Drilling
• In drilling process holes are
created in the metal through
circular cylinders. A twist drill is
used for accomplishing this task.

• 75% of the metal cutting

material is removed through the
drilling operation.

• The drill enters the work-piece

and cuts a hole which is equal to
the diameter of the tool that
was used for cutting the whole.
A drill has a pointed end which
can easily cut a hole in the work
piece.
 MILLING
• Milling is one of the fundamental
operations in machining.
• Milling is the process of machining
using rotary cutters to remove
material by advancing a cutter into a
work-piece. This may be done
varying direction on one or several
axes, cutter head speed, and
pressure.

• The work-piece here is the material

that is already shaped and it needs
milling. It is secured to the fixture,
ready for being milled. The cutter is
also secured to the machine. It has
sharp teeth and it rotates at a high
speed. The work-piece is fed to the
cutter and it removes the unwanted
metal from the piece.
 OTHER MACHINING OPERATINS…
• Boring
• Performed to enlarge a hole made previously.
• Used for circular internal profiles in hollow work pieces
• Sawing
• Sawing is an efficient bulk removal process and can produce near
net shape materials The process wastes little material
• Shaping
• Shaping is a process of producing flat or plane surface , which
may be horizontal or vertical
• Broaching
• Broaching is a similar technique to shaping with a long
multiple-tooth cutter and is used to machine internal an external
surfaces.

• Reaming
• An operation used to make an existing hole dimensionally more
accurate and/or to improve surface finish
 The Turning Process
Using Engine Lathes
• Operate on all Types of
Materials
• Use of single-point
tools
• Skilled Labor
• Low Production Rate
 History Of Lathe Machine
• Lathe forerunner of all machine tools
• First application was potter's wheel
– Rotated clay and enabled it to be formed into
cylindrical shape
• Very versatile
• Used for turning, tapering, form turning,
screw cutting, facing, drilling, boring,
spinning, grinding and polishing operations
 Types of Lathes
• Engine lathe
– Not production lathe, found in school shops, tool
rooms, and job shops
– Primarily for single piece or short runs
– Manually operated
Turret lathe
– Used when many duplicate parts required
– Equipped with multisided tool post (turret) to which
several different cutting tools mounted
• Single- and multiple-spindle automatic lathes
– Six or eight different operations may be performed on
many parts at the same time
– Will produce parts for as long as required
 Lathe and Its Various Components
A lathe is a machine tool which is used to rotate
a work piece to perform various operations
such as turning, facing, knurling, grooving etc.,
with the help of tools that are applied to the
work piece.
Block diagram of center
lathe
 Specification
• Height of center
• Length between the
centers
• Length of bed
• The swing diameter over
bed
• The swing diameter over
carriage
• Maximum diameter of bar
• Spindle speed, motor hp
 Main Parts of Lathe Machine
• . Headstock
• 2. Tailstock
• 3. Bed
• 4. Carriage
• 5. Lead Screw
• 6. Feed Rod
• 7. Chip Pan
• 8. Hand Wheel
 Parts of lathe

Tailstock Quick-Change Gearbox

 Parts of lathe

Carriage
Headstock

Cross-slide Apron
 Lathe Components
Bed: Usually made of cast iron. Provides a heavy
rigid frame on which all the main components are
mounted.
Ways: Inner and outer guide railsn that are
precision machined parallel to assure accuracy of
movement.
Headstock: mounted in a fixed position on the
inner ways, usually at the left end. Using a chuck,
it rotates the work.
Gearbox: inside the headstock, providing multiple
speeds with a geometric ratio by moving levers.
 Lathe Components
Spindle: Hole through the headstock to which
bar stock can be fed.
Chuck: 3-jaw (self centering) or 4-jaw
(independent) to clamp part being machined.
Tailstock: Fits on the inner ways of the bed and
can slide towards any position the headstock
to fit the length of the work piece. An optional
taper turning attachment would be mounted
to it.
Tailstock Quill: Has a Morse taper to hold a
lathe center, drill bit or other tool.
Carriage: Moves on the outer ways. Used for
mounting and moving most the cutting tools.
Cross Slide: Mounted on the traverse slide of
the carriage, and uses a handwheel to feed
tools into the workpiece.
 Lathe Components
Tool Post: To mount tool holders in which the
cutting bits are clamped.
Compound Rest: Mounted to the cross slide, it
pivots around the tool post.
Apron: Attached to the front of the carriage, it has
the mechanism and controls for moving the
carriage and cross slide.
Feed Rod: Has a keyway, with two reversing pinion
gears, either of which can be meshed with the
mating bevel gear to forward or reverse the
carriage using a clutch.
Lead Screw: For cutting threads.
Split Nut: When closed around the lead screw, the
carriage is driven along by direct drive without
using a clutch.
 Lathe Components
Quick Change Gearbox: Controls the movement
of the carriage using levers.
Steady Rest: Clamped to the lathe ways, it uses
adjustable fingers to contact the work piece
and align it. Can be used in place of tailstock
to support long or unstable parts being
machined.
Follow Rest: Bolted to the lathe carriage, it uses
adjustable fingers to bear against the
workpiece opposite the cutting tool to
prevent deflection.
 LATHES AND LATHE OPERATIONS
Workholding Devices and accessories - A chuck
• 3 or 4 jaws
• 3 jaws generally have a geared-scroll design that makes the jaws
self-centering. Used for round workpieces [bar stock, pipes tubing]
• 4 jaw independent chucks. Used for square, rectangular, or odd
shaped more ruggedly than three jaw chucks, four-jaw chucks are
used for heavy workpieces
• jaws can be reversed
• chucks: power actuated [pneumatically or hydraulically] or manual
chucks available in various designs & sizes: selection depends on:
1. type & speed of operation
2. workpiece size
3. production & accuracy requirements.
4. jaw forces requirements
 Workholding Devices and accessories - A Collet

• A collet is basically a longitudinally-split, tapered

bushing.
• The work piece (generally with a maximum
diameter of 25 mm) is placed inside the collet.
• The tapered surfaces shrink the segments of the
collet radically, tightening onto the work piece.
• One advantage to using a collect (rather than a
three- or four-jaw chuck) is that the collets grips
nearly the entire circumference of the part, making
the device well suited particularly for parts with
small cross sections.
 Workholding Devices and accessories – Face
Plates and Mandrels
• Face plates are used for clamping irregularly shaped work
pieces. The plates are round and have several slots and holes
through which the workpiece is bolted or clamped (Fig.
23.7d).
• Mandrels (Fig. 23.8) are placed inside hollow or tubular
workpieces and are used to hold workpieces that require
machining on both ends or on their cylindrical surfaces.
• Some mandrels are mounted between centers on the lathe.
a. both the cylindrical and the end faces of the work piece
can be machined
b. only the cylindrical surfaces can be machined
 Lathe Operation
• A single point cutting tool removes material from a rotating
workpiece to generate a rotationally symmetric shape
• Machine tool is called a lathe
• Types of cuts:
– Facing
– Contour turning
– Chamfering
– Parting (Cut-off) / Grooving
– Threading
• Lathe Operations
• Drilling
• Boring
• Knurling
 Facing
Facing is the process
of removing metal
from the end of a
work piece to
produce a flat
surface.

The work piece

rotates about its axis
and the facing tool is
fed perpendicular to
the axis of lathe.
 Contour Turning
• Instead of
feeding the tool
parallel to the
axis of rotation,
tool follows a
contour that is
not necessarily
straight (thus
creating a
contoured
form).
 Chamfering
It is a process of creating a
slope at the end of the
work piece.
This process is carried out
for removing the unwanted
metals and burrs after
turning operation.
Cutting edge cuts an
angle on the corner of
the cylinder, forming a
"chamfer"
 Parting (Cutoff) / Grooving
Parting off is the operation of
cutting a work piece after it
has been finished to the
desired dimension and shape.
In parting operation both feed
is fixed or locked and depth
of cut is controlled properly
until the work is cut off in
parts.
Tool is fed radially into
rotating work at some
location to cut off end of
part, or provide a groove
 Threading
Thread cutting is the operation of
producing helical groove on a
cylindrical surface.
Threads may be square or v
threads can be cut on a cylindrical
work piece.
The threads of any pitch, shape and
size can be cut on a lathe.
A single point cutting tool (V-tool
or square tool) is used to cut
threads on the work piece.
Pointed form tool is fed linearly
across surface of rotating workpart
parallel to axis of rotation at a
large feed rate, thus creating
threads
 Drilling
• Creates a round hole in a
workpart
• Contrasts with boring
which can only enlarge an
existing hole
• Cutting tool is called a drill
or drill bit Drilling

• Customarily performed on
a drill press, but can be
done on a vertical mill and
on a lathe
 Knurling

Knurling is the process

of embossing a
required shaped pattern
on the surface of the
work piece.
This diagram shows the
knurling tool pressed
against a piece of
circular work piece.
 Boring
• Boring is a process of producing
circular internal profiles on a hole
made by drilling or another process.
• It uses single point cutting tool
called a boring bar. In boring, the
boring bar can be rotated, or the
work part can be rotated. Machine
tools which rotate the boring bar
against a stationary work piece are
called boring machine

• Boring can be accomplished on a

turning machine with a stationary
boring bar positioned in the tool
post and rotating work piece held in
the lathe chuck ,