Machine tools basic mechanical engineering sem-II

What are machine tools?
• Machine tools are defined as a tool which while holding the cutting tool
would be able to remove metal from the workpiece.
• Material is removed from the workpiece in order to generate desired
shape. Some examples of M/C tools are milling cutter, drill bit, shaper etc.

Classifications based on capability of
production of machine tools
On the basis of production capability M/C tools can be classified into following four types
1.General purpose machine tools
They can be used for almost any type of application but, the speed of production is very low.
2.Production machine tools
Slightly more productive than general purpose M/C tools and are used for production purposes.
3.Special purpose machine tools
They are specially made for mass production and are designed for particular application.
4.Single purpose machine tools
They are used for highly automated production processes, where the production rate is very high. They are
least flexible.

Lathe Machines
Introduction
-The lathe is one of the earliest machine
tools, is also known as “Mother Machine
Tool”.
-A lathe is a machine tool which rotates
the work piece on its to perform various
operations such as facing, turning,
drilling, threading, knurling, and boring
etc.
-Lathes are used in woodturning,
metalworking, metal spinning.

Classification of lathes
1. Bench lathe
-it is a small lathe which can be mounted on a bench or cabinet.
-It is used for small and Precision work as it is very accurate.
-This usually provided with the attachment as provided to large lathe.
-This can be used to perform almost all the operations which can be
performed on a large lathe.

2. Speed lathe
-it is the simplest form of lathe.
-It consists of all the main components of a lathe but no provision for power feed.
-It has a gearbox, carriage and lead screw.
-The head stock spindle can rotate at a very high speed by a motor built inside the
head stock.
-The work is held between the centre and the tool is fed and actuated by hand.
-Speed lathe are widely used for woodworking, metal spinning, polishing etc.

3. Centre lathe or engine lathe
-it is the most widely used
lathe.
-In earlier version, steam
engines were used to supply the
power required for the machine,
it is name as engine lathe.
-It has an addition feature of
varying the speed of the lathes.
-In order to increase its utility
number of attachments can be
fitted on this lathe.

4. Tool Room lathe
-it is nothing but the same engine lathe with some extra attachment to make it suitable for
relatively more accurate and Precision type of work required to be carried out into room.
-This has smaller bed length than that of the engine lathe.
5. Special purpose lathe
-when the quantity to be produced is high, it is called as mass production.
-The Other types of productions are job production and batch production.
-For giving shape to a particular product to be produced on mass scale a lathe machine can
be design.
-The type of lathe exclusively used for this specific operation is known as special purpose
lathes.
-As the lathes are designed for specific operations it can give high rate of production.

6. Capstan and turret lathes
-These lathes have provision to hold several tools for performing wide range of
operation of job within a minimum time.
-These lathes are vastly used in mass production.
7. Automatic lathes
-These lathes are designed in such a way that all the working and job handling
movements of the complete manufacturing process for a job are done automatically.
-The operator’s participation is not required during the operation.

PRICIPLE PARTS OF A LATHE
The principle parts of
lathe are:
1.Bed
2.Headstock
3.Tailstock
5.Carriage
6.Feed Mechanisms

1. BED
-Bed is the baser or foundation of the lathe.
-It is heavy, rugged and single piece casting made to support the working parts of
the lathe.
-There are two sets of guide ways, (1) Outer ways and (2) Inner Ways.
-Outer ways is for the carriage and the inner ways for the tailstock.

2.HEADSTOCK
-Headstock is fastened on the inner ways at the left side of the bed.
-The headstock spindle, a hollow cylindrical shaft supported by bearings, provides a
drive from the motor to the working holding device.
-A live center and sleeve, a face plate, or a chuck can be fitted to the spindle nose.
-Spindle nose may have threaded design or flanged type.

3.TAILSTOCK
-Tailstock is situated on the inner ways at the right hand end of the bed, can be
moved towards or away from the operator.
-It can be locked in any position along the bed by tightening the clamp lever or nut.
-Tailstock spindle is a hollow tapered shaft, can be used to hold the dead center.
-Tailstock hand wheel is used to move the tailstock spindle in or out of the tailstock.

4.CARRIAGE
-Carriage controls and supports the cutting tool,
move to away towards the headstock.
-It have five major parts:
i.Saddle – H-shape, slides along the ways
between the headstock and tailstock.
ii.Cross Slide – fits over the saddle dovetail,
provides the cross movement to the cutting tool.
iii.Compound Rest – can be swivelled to any
angle for taper turning operations.
iv.Tool Post – clamps the turning tool or cutting
tool.
v.Apron – can be turned by hand to move the
carriage along the bed of the lathe.

5.FEED MECHANISM
-The movement of the tool relative to the work is termed as feed.
Three types of feed are:
i. Longitudinal feed – the tool moves parallel to the work i.e. towards or away from
the headstock.
ii. Cross Feed – the tool moves perpendicular to the work i.e. towards or away from
the operator.
iii. Angular Feed - the tool moves at the angle to the work. It is obtained by
swivelling operated.

Operations Performed on lathe
1.Turning
-It is the most common type of operation in all lathe
machine operations.
-Turning is the operation of removing the excess material
from the workpiece to produce a cylindrical surface to the
desired length.
-The job held between the centre or a chuck and rotating
at a required speed.
-The tool moves in a longitudinal direction to give the
feed towards the headstock with proper depth of cut.
-The surface finish is very good.

2.Facing
-It is an operation of reducing the length of
the workpiece by feeding the perpendicular to
the lathe axis.
-This operation of reducing a flat surface on
the end of the workpiece. For this operation,
regular turning tool or facing tool may use.
-The cutting edge of the tool should set to the
same height as the centre of the workpiece.

3.Chamfering
-It is the operation of getting a bevelled
surface at the edge of a cylindrical workpiece.
-This operation is done in case of bolt ends
and shaft ends.
-Chamfering helps to avoid damage to the
sharp edges and protect the operation getting
hurt during other operations.
-Chamfering on bolt helps to screw the nut
easily.

4.Forming
-It is the process of turning a convex, concave or
of any irregular shape.
-Form-turning may be accomplished by the
following method:
-Using a forming tool, Combining cross and
longitudinal feed and Tracing or copying a
template.
-Forming tools are not supposed to remove much
of the material and is used mainly for finishing
formed surfaces.
-Generally, two types of forming tools are used
straight and circular. Straight type is used for
wider surface and the circular type for narrow
surfaces.

5.Grooving
-It is the process of reducing the diameter of a
workpiece over a very narrow surface.
-It is done by groove tool.
-A grooving tool is similar to the parting-off
tool.
-It is often done at the end of a thread or
adjacent to a shoulder to leave a small
margin.

6.Knurling
-It is an operation of obtaining a diamond shape
on the workpiece for the gripping purpose.
-This is done to provide a better gripping surface
when operated by hands.
- It is done using a knurling tool.
-The tool consists of a set of hardened steel roller,
and it is held rigidly on the toolpost.
-Knurling is done at the lowest speed available on
a lathe.
-It is done on the handles and also in case of ends
of gauges.
-The feed varies from 1 to 2 mm per revolution.
-Two or three cut may be necessary to give the
full impression.

7.Drilling
-Drilling is the operation of producing a
cylindrical hole in a workpiece.
- It is done by a rotating tool, the rotating side
of the cutter, known as drilling drill.
-In this operation, The workpiece is revolving
in a chuck or a faceplate and the drill is held
in the tailstock drill holder or drill chuck.
-The feeding is adopted is affected by the
movement of the tailstock spindle.
-This method is adopted for the drilling
regular shaped workpiece.

8.Reaming
-Reaming is the operation of finishing and
sizing a hole which has been already drilled
or bored.
-The tool is used is called the reamer, which
has multi-plate cutting edges.
-The reamer is held on the tailstock spindle,
either directly or through a drill chuck and is
held stationary while the work is revolved at a
very slow speed.

9.Boring
-Boring is the operation of enlarging the hole
which is already drilled, punched or forged.
-It cannot produce a hole. Boring is similar to the
external turning operation and can be performed
in a lathe.
-In this operation, the workpiece is revolved in a
chuck or a faceplate and the tools which are fitted
to the tool post is fed into the work.
-It consists of a boring bar having a single point
cutting tool which enlarges the hole.
-It also corrects out of roundness of a hole.
-This method adopted for boring small-sized
works only.
-The speed for this process is slow.

10. Taper Turning
-A ”taper” is the uniform increase or decrease
in the diameter of the workpiece and
measured along with its length.
-Taper turning means to produce a conical
shape by a gradual reduction in diameter from
a cylindrical workpiece.

11. Thread cutting
-It is the important operation in the lathe to obtain the continuous
”helical grooves” or ” threads’‘.
-When the threads or helical grooves are formed on the out surface
of the workpiece is called external thread cutting.
-When the threads or helical grooves are formed on the inner surface
of the workpiece is called internal thread cutting.
-The workpiece is rotating between the two centres i.e., live centre
and dead centre of the lathe.
-Here the tool is moved longitudinally to obtain the required type of
the thread.
-When the tool is moved from right to the left we get the left-hand
thread.
-Similarly, when the tool is moved from left to the right we get the
right-hand thread.
-Here the motion of the carriage is provided by the lead screw.
-A pair of change gears drives the lead screw and by rotating the
handle the depth of cut can be controlled.

Drilling Machines
Introduction
-Drilling is an operation in which holes are produced in the work by means of revolving
tool called as drill. The holes produced by drilling operation are not perfect. It is
considered as a roughing operation.
-The finishing of the hole is carried out by an operation known as reaming.
-Reaming operation is carried out with the help of tool called as reamer.
-Machine which is used for performing drilling operation is called drilling machine.

Principle of drilling
-The metal cutting operation which produce holes in the work
using drill known as a drilling.
-The drill is provided with two cutting edges. In order to remove
material in the form of chips, the drill is given to motions that is
rotary motion and linear motion simultaneously.
a) rotary motion:- the drill is provided with rotary motion about
its axis. This motion is known as primary or cutting motion.
b) linear motion:- the work is mounted on the table of the
machine and the drill is made to fed in the work by giving it a linear
motion. This motion is called as feed and it control the thickness
of the chip.

Classification of drilling machines
1.Portable drilling machine (or) Hand drilling machine
2.Sensitive drilling machine (or) Bench drilling machine
3.Upright drilling machine
4.Radial drilling machine
5.Gang drilling machine
6.Multiple spindle drilling machine
7.Deep hole drilling machine

1.Portable Drilling Machine
-Portable drilling machine can be carried and used anywhere in the workshop.
-It is used for drilling holes on workpieces in any position, which is not possible in
a standard drilling machine.
-The entire drilling mechanism is compact and small in size and so can be carried
anywhere.
-This type of machine is widely adapted for automobile built-up work. The motor
is generally universal type.
-These machines can accommodate drills from 12mm to 18 mm diameter. Portable
drilling machines are operated at higher speeds.

2.Sensitive Drilling Machine
-It is designed for drilling small holes at high speeds in light jobs.
- High speed and hand feed are necessary for drilling small holes.
-The base of the machine is mounted either on a bench or on the floor
by means of bolts and nuts.
-It can handle drills upto 15.5mm of diameter.
-The drill is fed into the work purely by hand .
-The operator can sense the progress of the drill into the work
because of hand feed. The machine is named so because of this
reason.
-A sensitive drilling machine consists of a base, column, table,
spindle, drillhead and the driving mechanism.

Base – The base is made of cast iron and so can withstand vibrations. It may be
mounted on a bench or on the floor. It supports all the other parts of the machine on
it.
Column – The column stands vertically on the base at one end. It supports the work
table and the drill head. The drill head has drill spindle and the driving motor on
either side of the column.
Table – The table is mounted on the vertical column and can be adjusted up and
down on it. The table has ‘T’-slots on it for holding the workpieces or to hold any
other work holding device. The table can be adjusted vertically to accommodate
workpieces of different heights and can be clamped at the required position.
Drill head – Drillhead is mounted on the top side of the column. The drill spindle
and the driving motor are connected by means of a V-belt and cone pulleys. The
motion is transmitted to the spindle from the motor by the belt. The pinion attached
to the handle meshes with the rack on the sleeve of the spindle for providing the
drill the required downfeed. There is no power feed arrangement in this machine.
The spindle rotates at a speed ranging from 50 to 2000 r.p.m.

3.Upright Drilling Machine
-The upright drilling machine is designed for handling medium
sized workpieces.
-Though it looks like a sensitive drilling machine, it is larger and
heavier than a sensitive drilling machine.
-Holes of diameter upto 50mm can be made with this type of
machine. Besides, it is supplied with power feed arrangement.
-For drilling different types of work, the machine is provided with a
number of spindle speeds and feed.
There are two different types of upright drilling machines acc
ording to the cross-section of the column and they are Round
column section upright drilling machine and Box column section
upright drilling machine
The main parts of a upright drilling machine are : base, column,
table and drillhead.

Base – Base is made of cast iron as it can withstand vibrations set by the cutting action. It
is erected on the floor of the shop by means of bolts and nuts. It is the supporting member as
it supports column and other parts on it. The top of the base is accurately machined and has
‘T’-slots. When large workpieces are to be held, they are directly mounted on the base.
Column – Column stands vertically on the base and supports the work table and all driving
mechanisms. It is designed to withstand the vibrations set up due to the cutting action at high
speeds.
Table – Table is mounted on the column and can be adjusted up and down on it. It is provided
with ‘T’-slots for workpieces to be mounted directly on it. Table may have the following
adjustments
Vertical adjustment obtained by the rack on the column and a pinion in the table
Circular adjustment about its own axis. After the required adjustments are made, the table is
clamped in position.
Drill head – The drillhead is mounted on the top of the column. It houses the driving and
feeding mechanism of the spindle. The spindle can be provided with hand or power feed .
There are separate hand wheels for quick hand feed and sensitive hand feed. The handle is
spring loaded so that the drill spindle is released from the work when the operation is over.

4.Radial Drilling Machine
-The radial drilling machine is intended for drilling on
medium to large and heavy workpieces.
-It has a heavy round column mounted on a large base.
-The column supports a radial arm, which can be raised or
lowered to enable the table to accommodate workpieces of
different heights.
-The arm, which has the drilllhead on it, can be swung
around to any position.
-The drill head can be made to slide on the radial arm. The
machine is named so because of this reason.
-It consists of parts like base, column, radial arm, drillhead
and driving mechanism.

Base – The base is a large rectangular casting and is mounted on the floor of the shop. Its top is
accurately finished to support a column at one end and the table at the other end. ‘T’-slots are
provided on it for clamping workpieces.
Column – The column is a cylindrical casting, which is mounted vertically at one end of the
base. It supports the radial arm and allows it to slide up and down on its face. The vertical
adjustment of the radial arm is effected by rotating a screw passing through a nut attached to the
arm. An electric motor is mounted on the top of the column for rotating the elevating screw.
Radial arm – The radial arm is mounted on the column parallel to the base and can be adjusted
vertically. The vertical front surface is accurately machined to provide guideways for the
drillhead. The drillhead can be adjusted along these guideways according to the location of the
work. In some machines, a separate motor is provided for this movement. The arm may be
swung around the column. It can also be moved up and down to suit workpieces of different
heights.
Drillhead – The drill head is mounted on the radial arm and houses all mechanism for driving
the drill at different speeds and at different feed. A motor is mounted on top of the drillhead for
this purpose. To adjust the position of drill spindle with respect to the work, the drillhead may be
made to slide on the guideways of the arm. The drillhead can be clamped in position after the
spindle is properly adjusted.

5.Gang Drilling Machine
-Gang drilling machine has a long common table
and a base.
- Four to six drillheads are placed side by side.
-The drillheads have separate driving motors.
-This machine is used for production work.
-A series of operations like drilling, reaming,
counterboring and tapping may be performed on
the work by simply shifting the work from one
position to the other on the work table.
-Each spindle is set with different tools for
different operations.

6.Multiple Spindle Drilling Machine
-This machine is used for drilling a number of holes in a workpiece simultaneously and for
reproducing the same pattern of holes in a number of identical pieces.
-A multiple spindle drilling machine also has several spindles.
-A single motor using a set of gears drives all the spindles.
-All the spindles holding the drills are fed into the work at the same time.
- The distances between the spindles can be altered according to the locations where holes are to be
drilled. Drill jigs are used to guide the drills.
7.Deep Hole Drilling Machine
-A special machine and drills are required to drill deeper holes in barrels of gun, spindles and
connecting rods.
-The machine designed for this purpose is known as deep hole drilling machine.
-High cutting speeds and less feed are necessary to drill deep holes.
-A non- rotating drill is fed slowly into the rotating work at high speeds.
-Coolant should be used while drilling in this machine.
-There are two different types of deep hole drilling machine.

Operations Performed on Drilling
Machines
1. Drilling
-Drilling is the operation of producing a cylindrical hole of required
diameter and depth by removing metal by the rotating edge of a cutting
tool called drill.
- Drilling is one of the simplest methods of producing a hole.
-Drilling does not produce an accurate hole in a workpiece.
-The internal surface of the hole generated by drilling becomes rough
and the hole is always slightly oversize due to vibration of the spindle
and the drill.
-A hole made by a drill of size 12mm will measure approximately upto
12.125mm and by a drill of size 22mm will measure upto 22.5mm.

2.Reaming
-The size of hole made by drilling may not be accurate and the internal
surface will not be smooth.
-Reaming is an accurate way of sizing and finishing a hole which has
been previously drilled by a multi point cutting tool known as reamer.
-The surface obtained by reaming will be smoother and the size
accurate.
-The speed of the spindle is made half that of drilling.
-Reaming removes very small amount of metal ( approx 0.375 mm).
- In order to finish a hole and bring it to the accurate size, the hole is
drilled slightly undersize.

3.Boring
-Boring is the operation enlarging the diameter of the previously made hole. It is done for
the following reasons.
-To enlarge a hole by means of an adjustable cutting This is done when a suitable sized drill
is not available or the hole diameter is so large that is cannot be ordinarily drilled.
-To finish a hole accurately and bring it to the required size.
-To machine the internal surface of the hole already produced in casting.
-To correct out of roundness of the hole.
-To correct the location of the hole as the boring tool follows independent path with respect
to the hole.
-Boring tool is a tool with only one cutting edge.
-The tool is held in a boring bar which has a taper shank to fit into the spindle or a socket.
-For perfectly finishing a hole, the job is drilled undersize slightly.
-Boring operation in some precise drilling machine is performed to enlarge the holes to an
accuracy of 0.00125mm.
-The spindle speed during boring should be adjusted to be lesser than that of reaming.

4.Counterboring
-Counterboring is the operation of enlarging the end of the hole
cylindrically.
-The enlarged hole forms a square shoulder with the original
hole.
-This is necessary in some cases to accommodate the heads of
bolts, studs and pins.
-The tool used for counter boring is known as counter bore.
-The counterbores are made with cutting edges which may be
straight or spiral.
-The cutting speed for counterboring is atleast 25% lesser than
that of drilling.

5.Countersinking
-Countersinking is the operation of making a cone shaped enlargement
at the end of the hole.
-The included angle of the conical surface may be in the range of 60° to
90°.
-It is used to provide recess for a flat headed screw or a counter sunk
rivet fitted into the hole.
-The tool used for counter sinking is known as a countersink.
-It has multiple cutting edges on its conical surface.
-The cutting speed for countersinking is 25% lesser than that of
drilling.

6.Spot Facing
-Spot facing is the operation of smoothing and squaring
the surface around a hole.
-It is done to provide proper seating for a nut or the
head of a screw.
-A counterbore or a special spot facing tool may be
employed for this purpose.

7.Tapping
-Tapping is the operation of cutting internal threads by
means of a cutting tool called ‘tap’.
-Tapping in a drilling machine may be performed by
hand or by power.
- When the tap is screwed into the hole, it removes
metal and cuts internal threads which will fit into
external threads of the same size.

Milling Machines
• Milling machine is used to generate required shape on the
workpiece by using a tool known as milling cutter. Milling
cutter is a multi-point cutting tool. The cutter is fed against
workpiece to remove the material and gives the work in
desired shape.
Principle of milling
• The work piece is mounted in a work holding device. The
work holding device is mounted on the table which is given
reciprocating motion. The milling cutter is given a rotary
motion and is a fed against the work. Which removes the
material from the workpiece in the form of chips and give
the required ship to the workpiece.

Types of Milling process
1.Up milling
• Work piece advances against the rotating cutter.
• Chips are progressively thicker.

2.Down milling
 Work piece is fed in the same direction as that
of the cutter tooth.
 Cutter enters top of the work piece and
removes the chip that gets progressively thinner.

Difference between Up and Down
Milling
 Work piece is fed in
same direction of that
of cutter.
 Chips are progressively
thinner.
 Strong clamping is not
required since the
cutting force is directed
downwards and keeps
work piece pressed to
table.
 Good surface finish and
used for soft materials.
 Work piece is fed in
opposite direction of
that of cutter.
 Chips are progressively
thicker.
 Strong clamping is
required since the
cutting force is directed
upwards and tends to
lift the work piece.
 Poor surface finish and
used for hard materials.
Up milling Down milling

Classifications of milling Machines
• Column and knee type
• Fixed bed type
• Planer type
• Special type

Column and knee type milling machine
• This type milling machine is the most commonly used machine due
to flexibility and easier set up.
• The machine consist of knee made of cast iron which can slide
over vertical column.
• To accommodate large size workpiece knee can made to move up
and down.
• Table mounted on the knee can have longitudinal and cross feed
motion.
• The column houses the motor, feed mechanism gear box etc.
• A milling cutter is mounted on a spindle is known as arbor
• The front end of the arbor is fixed in the arbor support.
• The cutter is given rotary motion through arbor and fed against the
work

• Fig. shows vertical column knee type milling
machine.
• The construction is similar to that of horizontal
machine except for the spindle type and location.
• The spindle is located in vertical direction and is
suitable for holding cutters having shank.
• The vertical machine is relatively more flexible
and suitable for machining complex cavities.

Operations on Milling Machines
• 1. Plain milling
In plain milling operation on a flat surface produce on
the workpiece. This flat surface produced is parallel to
the axis of the milling cutter.
2. Face milling
• In case of face milling operation machining is carried
out on the surface perpendicular to the axis of the
cutter. The cutter used for this operation is called as
the face milling cutter

3. Side milling
• The sides of surface of the workpiece are
machine using side milling cutter
4. Angular milling
• By angular milling operation angular surface
is obtained. A cutter is fed against the
workpiece generating an angular surface.

5. End milling
• End milling operation is carried out using and
end milling cutter. This operation is used to
produce grooves, key ways, flat surfaces on the
workpiece.
6. Gang milling
• In gang milling operation number of cutters are
used. These cutters are mounted on the same
Arbor. The gang milling operation is preferred
where production is mass production of same
components.

7. Straddle milling
• In straddle milling operation flat vertical
surface are produced. Both sides of the
workpiece are simultaneously milled using two
cutters. Straddle milling operation is used for
production square, hexagonal surfaces.
8. keyway/slots/ groove milling
• Key ways, grooves, slots etc. are produced by
keyway milling operation. Open slots can be
obtained by use of end milling cutter, side
milling cutter or plain milling cutter.

9. Form milling
• In case of form milling form milling cutter is used. The
cutter has same shape of the workpiece to be machined.
10. Profile milling
• Profile milling operation is used to reproduce an outline of
the template or Complex shape of a master die on work
piece. An end milling cutter is very widely used for this
operation.
11. T slot milling
• T slot milling operation is used to produce T slots in the
workpiece. A plain Slot is first machined in the workpiece.
Then shank of T slot milling cutter is introduced in the
slot machined earlier and then a second slot perpendicular
to first slot is created, thereby completing T-slot.

Machine tools basic mechanical engineering sem-II

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