||Jai Sri Gurudev||
Sri Adichunchanagiri Shikshana Trust (R)
SJB INSTITUTE OF TECHNOLOGY
An Autonomous Institute under Visvesvaraya Technological University, Belagavi)
Approved by AICTE, New Delhi, Recognized by UGC, New Delhi with 2 (f) & 12 (B)
Accredited by NAAC with ‘A+’ Grade, Accredited by National Board of Accreditation)
No. 67, BGS Health & Education City, Dr. Vishnuvardhan Road, Kengeri, Bengaluru-560060.
Department of Mechanical Engineering
Subject
ESSENTIALS OF MECHANICAL ENGINEERING
23MET14A
MODULE 2
Machine Tool Operations
Faculty:
Dr. Naveena kumar R. R.
Assistant Professor
Department of Mechanical Engineering
Essentials of Mechanical Engineering
MODULE 2
MACHINE TOOL OPERATIONS
Lathe: Principle of working of a centre lathe, lathe operations: Turning, facing,
knurling, thread cutting, taper turning by swivelling the compound rest,
Drilling Machine: Working of simple drilling machine, drilling operations:
drilling, boring, reaming,tapping, counter sinking, counter boring,
Milling Machine: Principle, Working and types of milling machine, milling
operations: plane milling, endmilling and slot milling.
MACHINE TOOL OPERATIONS
Machine Tools:
When machines perform the metal cutting operations by the cutting tools mounted on them,
they are called “Machine tools”. A machine tool may be defined as a power-driven machine
which accomplishes the cutting or machining operations on it. The machine tools used for
most of the machining processes are Lathe, Drilling, Milling and Grinding machines.
LATHE
The Lathe is one of the oldest machine tools used to produce cylindrical objects. The modern
engine lathe is first developed in the year 1797 by an Englishman Henry Maudslay. The
main function of the lathe is to removal of metal from a work piece of work to give it a
required shape and size. This is accomplished by holding the work securely and rigidly on
the machine and then turning it against a cutting tool which will remove the material from
the work in the form of a chip. To cut the material properly, the tool should be harder than
that of the material of the workpiece.
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Classification of Lathe Machine Tools:
Lathes are classified based on their design, construction and application. Following are
some of the important lathes used in industries.
1. Speed Lathe
5. Capstan & Turret Lathe
2. Engine Lathe
6. Special Purpose Lathe
3. Bench Lathe
7. Automatic Lathe
4. Tool Room Lathe
8. CNC Lathe (Turning Centres)
Construction & Working Principle of Centre Lathe/ Engine Lathe:
The schematic arrangement of the Centre or Engine Lathe is as shown in the following
figure. The major parts of a centre lathes are:
1. Bed & Guideways
2. Headstock
3. Tailstock
4. Lathe bed
5. Carriage Assembly
6. Driving mechanism & Feeding mechanism
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Bed: The bed forms, the base of the machine. The headstock and the tail stocks are located
at either end of the bed and the carriage rest over the lathe bed and slides on it. The guide
ways of the lathe bed may be flat and inverted V type having an include angle of 90 degree.
Headstock: The headstock is secured permanently on the inner waves, at the left end of the
lathe bed and it provides mechanical means of rotating the work at multiple speeds, It
contains a hallow spindle and mechanism for driving and altering this spindle speed. All the
parts are housed within the headstock casting.
Tailstock: The tail stock is located on the inner waves at the right end and top of the bed
ways. This has two main uses.
•
It supports the other end of the workpiece. When it is being machine between the
centres.
•
It holds the tool for performing operations, such as drilling. Riming tapping etc, to
accommodate different length of work.
The body of the Tailstock can be adjusted along the length of the bed-ways by sliding it to
the desired position, and can be locked on a lathe bed-way.
Carriage: The carriage of a lathe has several parts that serves to support, move and control
the cutting tool. It consists of the following parts saddle cross, slide, Compound slide, tool
post and apron.
Saddle: The saddle is an H- shape casting that fits over the bed and slides along the base. It
carries the cross slide and tool post.
Cross slide: It is mounted on the saddle and enables the movement of the cutting tool
laterally, across the lathe bed by means of a cross feed handle. It also serves as the support
for the compound rest.
Compound rest: The compound rest is mounted on top of the cross slide and has a circular
base graduated in degrees. It is used for obtaining angular cuts and short tapers. As well as
convenient positioning of the tool at the work.
The tool post: This is located on top of the compound slide to hold the tool and enable it to
be adjusted to convenient Working position,
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Feed mechanism: The movement of the tool related to the work is called as a feed. The feed
can be given either by the hand, or by automatic or powered feed. To get the automatic feed,
carriage is engaged to feed rod. while for cutting threads, carriage is engaged to screw rod.
Some of the operations carried out on a lathe machine are as listed below;
1. Facing
2. Turning
3. Taper turning
4. Knurling
5. Thread cutting
1. Facing:
Is the operation of machining the ends of a piece of the work to produce a flat surface
perpendicular with the axis. This is also used to cut the work to the required length. The
operation involves feeding the tool perpendicular to the axis of rotation of the work piece. A
regular cutting tool may be used for facing a large work piece. The cutting edge should be
set at the same height as the centre of the work piece. A properly ground facing tool is
mounted in a tool holder in the tool post to accomplish facing operation.
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2. Turning Operation:
Figure: Turning Operation
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 operation and make the operation
faster and economical. Plain turning operations are generally performed in two steps-rough
and finish turning.
Rough turning is usually done for rolled, cast or forged parts to remove the uneven or sandy
or rough surface on the jobs. A roughing tool does roughing and used for excess stock
removal. For finishing a tool with slightly round cutting edge is used. The depth of cut rate is
at the range of 0.2 to 1 mm and the feed rate between 0.1 to 0.3 mm.
3. Taper turning:
Taper turning is an operation to produce conical surface on the work piece. This can be
machined by either work piece inclined to the axis of the lathe or tool moving inclined to the
axis of the lathe.
There are many methods for taper turning
a) By swivelling the compound rest.
b) By offsetting the tail stock.
c) By taper turning attachment.
d) By using form tool/ Broad nose tool
e) Combination of Longitudinal and Transverse feed movement.
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a) Taper Turning by Swiveling the compound Tool Rest
Figure: Taper turning by Swiveling the compound rest method
The work pieces which require steep taper for short lengths the taper turning was done by
swiveling the compound rest method. In this method the compound tool rest is swiveled to
the required taper angle and then locked in the angular position. The carriage is also locked
at that position. For taper turning the compound rest is moved linearly at an angle so that
the cutting tool produces the tapered surface on the work piece. This method is limited to
short taper lengths due to the limited movement of the compound tool rest.
The taper angle is calculated by,
Where,
D= bigger diameter of the taper (mm)
d= smaller diameter of the taper (mm)
L= Length of the taper (mm)
5. Knurling
This is not a machining operation at all, because it does not involve material removal.
Instead, it is a metal forming operation used to produce a regular crosshatched pattern in
the work surface. It is done on certain components for effective gripping to prevent it from
slipping while handling it, example is thumbscrews, etc. The knurling process is shown in
Figure 3. The knurling tool consists of a set of hardened steel rollers in a holder with the
teeth cut on their surface in a definite pattern. The tool is held rigidly on the tool post and
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the rollers are pressed against the revolving workpiece to squeeze the metal against the
multiple edges. The speed used during knurling should be very low and plenty of lubricant
should be used.
6. Thread cutting
Thread cutting is the operation of producing a helical groove of specific shape on a
cylindrical surface. Figure shows the setup of a lathe for thread cutting. Thread cutting
operation is done using a single point tool called thread cutting tool. Threads are cut using
lathes by advancing the cutting tool at a feed exactly equal to the thread pitch. For
producing threads of pitch in mm, the tool must travel a distance equal to pitch in mm as the
workpiece makes one complete rotation. The single-point cutting tool cuts in a helical band,
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which is actually a thread. In FPS system, threads are specified as threads per inch or TPI.
For example, if a workpiece is having four threads per inch then the pitch of the thread is
equal to ¼ inch. The definite relative rotary and linear motion between the workpiece and
tool is achieved by locking or engaging the carriage with the lead screw through a screw and
nut mechanism and fixing a gear ratio between the head stock spindle and lead screw. This
is done by using change gear mechanism or a gearbox between the spindle and lead screw.
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DRILLING MACHINE
Introduction
Drilling machine is one of the most important machine tools in a workshop. It was designed
to produce a cylindrical hole of required diameter and depth on metal workpieces. Though
holes can be made by different machine tools in a shop, drilling machine is designed
specifically to perform the operation of drilling and similar operations. Drilling can be done
easily at a low cost in a shorter period of time in a drilling machine.
Drilling can be called as the operation of producing a cylindrical hole of required diameter
and depth by removing metal by the rotating edges of a drill. The cutting tool known as drill
is fitted into the spindle of the drilling machine. A mark of indentation is made at the
required location with a centre punch. The rotating drill is pressed at the location and is fed
into the work. The hole can be made upto a required depth.
Construction of a drilling machine
The basic parts of a drilling machine are a base, column, drill head and spindle. The base
made of cast iron may rest on a bench, pedestal or floor depending upon the design. Larger
and heavy duty machines are grounded on the floor. The column is mounted vertically upon
the base. It is accurately machined and the table can be moved up and down on it. The drill
spindle, an electric motor and the mechanism meant for driving the spindle at different
speeds are mounted on the top of the column. Power is transmitted from the electric motor
to the spindle through a flat belt or a ‘V’ belt.
Types of drilling machines
Drilling machines are manufactured in different types and sizes according to the type of
operation, amount of feed, depth of cut, spindle speeds, method of spindle movement and
the required accuracy.
The different types of drilling machines are:
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. Multiple spindle drilling machine
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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 drill head 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, drill head and
driving mechanism. A radial drilling machine is illustrated in Figure.
Drilling machine operations
Though drilling is the primary operation performed in a drilling machine, a number of
similar operations are also performed on holes using different tools. The different
operations that can be performed in a drilling machine are:
1. Drilling
4. Counter boring
2. Reaming
5. Countersinking
3. Boring
6. Tapping
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1. Drilling
Drilling is an operation of producing a cylindrical hole by removing metal by rotating edge
of cutting tool call as Drill. This is one of the simplest methods of producing a hole. It
doesn’t produce an accurate hole in a workpiece due to the vibration of the spindle and drill.
2. Reaming
It is a precise method for estimating and completing an opening which has been recently
bored. The tool uses for reaming is known as the reamer which has multiple cutting edges.
It can’t originate a hole. It basically follows the way which has been recently bored and
expels an extremely limited quantity of metal. The material removes through this process is
around 0.375 mm and for accurate work this should not exceed 0.125 mm.
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3. Counter sinking:
Counter sinking is the operation of making a cone shaped enlargement at the end of a hole
to provide recess for a flat head screw or a countersunk rivet. The counter-sunks (tools used
for counter sinking) carry included angles of 60°, 82° or 90° and the cutting edges of the tool
are formed at the conical surface.
4. Boring operation
The purpose of boring is to enlarge a hole by means of an adjustable cutting tool with only
one cutting edge. It machine the internal surface of a hole already produced in casting. To
correct out of roundness of the hole. To address the area of the gap as the drilling apparatus
follows an autonomous way as for the gap.
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5. Tapping operation
This is an operation of cutting internal threads by means of cutting tool called a tap.
A tap might be considered as a jolt with precise strings cut on it. The threads act as
cutting edges which are solidified and ground.
It removes metal and cuts internal threads which will fit into outer threads of the same
size.
6. Counter boring
Counter boring is the operation of enlarging one of an existing hole concentric with the
original hole with a square bottom.
A counter tool is known as counter bore it has a pilot.
The pilot enters the previously drilled holes and aligns the tool so that the counter bored
hole is concentric with the existing one.
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MILLING MACHINE
The milling machine is believed to come into existence in 17th century. It was used by the
clockmakers at that time. Then in the 18th century in the United States, a machine was used
which was similar to the lathe machine but in this machine, the cutting tool is used to rotate
and the workpiece uses to remain stationary.
Milling Machine Definition:
The milling machine is a type of machine which removes the material from the
workpiece by feeding the work past a rotating multipoint cutter. The metal removal
rate is higher very high as the cutter has a high speed and many cutting edges.
It is the most important machine in the tool room as nearly all the operations can be
performed on it with high accuracy.
Milling Machine Application or Uses:
Milling Machine is used for Machining flat surfaces, Slotting, Contoured surfaces. It is also
useful for making Complex and irregular areas, Revolution surface, Gear cutting,
Machining external and internal threads. Machining helical surfaces of various crosssections and many more.
Milling Machine Parts:
1. Base:
The base is the part upon which the whole machine parts are being mounted. It is a
type of foundation for the machine.
The base is mostly made up of cast iron, so it has good strength and rigidity. It also helps
in the absorption of shocks. Cutting fluid can also be stored in the base.
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2. Column:
The main supporting frame which consists of all the driving mechanisms and the motor is
called the column.
The driving mechanism usually consists of a cone pulley mechanism in which the v-belt is
being used to connect it to the motor.
Further by using this driving mechanism the speed of the machine can control as per our
requirement.
3. Knee:
The knee shape is quite similar to that of the human body knee. This is an important part of
this machine that supports the other parts like the saddle and table.
It is attached to the column and has guideways by which it can move up and down with the
help of the elevating screw for adjusting its height.
4. Saddle:
The saddle is present on the top of the knee which further carries the table. Its basic
function is to support the table.
A saddle can slide on the guideways which are exactly at 90 degrees to the column
face. Saddle moves crosswise(in or out) on guideways provided on the knee.
5. Table:
The table is present on the top of the saddle. The table consists of T-slots or
sometimes fixtures are used for holding up the workpiece on the table. A table can
travel longitudinally in a horizontal plane.
6. Over-arm:
It is also called the over-hanging arm. Overarm is present at the top of the column. The basic
function of the over-arm is to support the arbor and spindle.
7. Spindle or Arbor:
The top portion of the column contains the spindle. The spindle is also an important part of
the machine as it is the part where the multipoint cutter is attached.
Power required for the rotation of the spindle is obtained from the motor through the belt,
gear, and clutch assembly.
Milling Machine Working Principle:
▪
Milling machine employed in the metal removing operation in which the work is rigidly
clamped on the table of the machine and the revolving cutter which has multiple teeth is
mounted on the arbor.
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▪
The cutter revolves at high speed and the work is fed slowly past the cutter.
▪
The work can be fed in a vertical, longitudinal, or cross direction depending upon the type of
milling machine being used.
▪
As the work proceeds, the cutter-teeth removes the metal from the surface of the
job(workpiece) to produce the desired shape.
Up Milling and Down Milling:
In CNC machining, the rotation direction of the milling cutter is generally constant, but the
feed direction is changed. There are two common phenomena in milling: down milling and up
milling.
The milling cutter’s cutting edge is subjected to an impact load each time it is plunged. In
order to successfully mill, you must consider the correct way of contact between the cutting
edge and the material during cutting in one cut.In the milling process, the workpiece is fed in
the same or opposite direction as the rotation direction of the milling cutter, which affects the
cutting in and out of the milling and whether the method is down milling or up milling.
Up milling
In up milling, the cutting tool feeds in the opposite direction to its direction of rotation.
The chip thickness gradually increases from zero until the end of the cutting. The cutting
edge must be forcibly cut in, resulting in scratching or polishing effects due to friction, high
temperatures, and frequent contact with the work-hardened surface caused by the front
cutting edge. All this will shorten tool life.
Thick chips and higher temperatures generated during cutting out of the cutting edge will
cause high tensile stresses, which will shorten the tool life and the cutting edge will usually
be damaged quickly. It can also cause chips to stick or weld to the cutting edge, which can
then carry it to the starting position for the next cut, or cause the cutting edge to
momentarily chip.
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Cutting forces tend to push the cutter and the workpiece away from each other, and radial
forces tend to lift the workpiece from the table.
When the machining allowance changes significantly, up milling may be more advantageous.
When using ceramic inserts to process high-temperature alloys, up-milling is also
recommended, because ceramics are more sensitive to the impact generated when cutting
into the workpiece.
Down milling
In down milling, the cutting tool is fed in the direction of rotation. As long as machine tools,
fixtures and workpieces allow it, down milling is always the preferred method.
In edge down milling, the chip thickness will gradually decrease from the beginning of
cutting and eventually reach zero at the end of cutting. This prevents the cutting edge from
rubbing against the surface of the part before participating in cutting.
Large chip thicknesses are advantageous, as cutting forces tend to pull the workpiece into
the milling cutter, keeping the cutting edge cutting. However, because the milling cutter is
easily pulled into the workpiece, the machine needs to handle the table feed gap by
eliminating backlash. If the milling cutter is pulled into the workpiece, the feed will
unexpectedly increase, which may result in excessive chip thickness and chipping of the
cutting edge. In these cases, consider using up milling.
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Milling Machine Operations:
Following different operations can be perform on milling machine:
1. Face Milling Operation
9. End Milling Operation
2. Straddle Milling Operation
10. Slot Milling Operation
3. Side Milling Operation
11. Gear Cutting Operation
4. Plain Milling Operation
12. Saw Milling Operation
5. Angular Milling Operation
13. Cam Milling Operation
6. Gang Milling Operation
14. Thread Milling Operation
7. Profile Milling Operation
15. Helical Milling Operation
8. Form Milling Operation
1. Plain Milling or Slab Milling Operation:
Plain or slab milling is a process in which the plain, horizontal or flat surfaces are produced,
which are parallel to the axis of the rotation of the cutter. A peripheral mill cuter is used for
performing the slab milling operation.
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3. Face Milling Operation:
It is a type of milling operation in which the layer of material is removed from the face of the
material. The end milling cutter is preferred for performing face milling operations.
In Face Milling operation the teeth for cutting are present on both the periphery and the
face of the cutter.
The axis of rotation of the cutter is perpendicular to the work surface. In face milling most of
the cutting is done by the periphery portions of the teeth, the face portion provides finishing
the action.
4. End Milling Operation:
End milling operation make flat vertical surfaces, flat horizontal surfaces and further flat
surfaces make an angle as of table surface by milling cutter name as end mill. This operation
is if possible carried out on vertical milling machine.
End milling is aprocess
used to create flat surfaces
on a workpiece using a
cutting tool called an end
mill. This process can
produce flat vertical
surfaces, flat horizontal
surfaces, and angled
surfaces relative to the
machine table. End milling
is typically performed on a
vertical milling machine,
where the spindle is
oriented vertically for
precise material removal.
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5. Gang Milling Operation:
This is a type of milling operation in which multiple cutters are being mounted on the same
arbor to produce the desired shape on the workpiece.
6. Slot Milling Operation
Slot milling operation make grooves, keyways, slots of unstable shapes with sizes is calling
slot milling operation. This operation can use any kind of milling cutter similar to plain
milling cutter, metal slitting saw or side milling cutter. Choose of a cutter depends upon kind
and size of slot or groove to be created. Right placement milling cutter is extremely main in
this operation as axis of cutter must be at middle of geometry of slot or groove to be created.
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