INTRODUCTION OF LATHE
INTRODUCTION
In previous chapters, we have seen that with the help of forging and casting processes, we can manufacture
machine parts of different shapes and sizes. However, parts so manufactured have poor geometry and
size control (i.e., tolerance on dimensions) and their surface finish is not very good. Hence, in most
cases, castings and forgings undergo machining before these parts can be assembled with other parts to
form a complete machine like cycle or motor car etc.
In machining, we use a machine tool like lathe or shaper and a cutting tool made of a much
harder material than the material of the part to be machined. Material removed from the part is achieved
by the relative movement between the cutting tool and the part. The cutting tool is given a sharp cutting
edge and it is forced to penetrate inside the work piece surface to a small depth. The relative motion
between the tool and work piece results in a thin strip of material being sheared off from the work piece
reducing the thickness of the work piece. This process has to be repeated several times before the entire
surface of the work piece can be covered and reduced in depth. The thin strip of the material sheared
from the work piece is called ‘chip’. It must be understood that chips are produced by shearing action
and not by cutting. Subtantial amount of power is required for machining. The function of the machine
tool is to provide this power and the required motion of work piece relative to the tool.
In some cases of machining, motion is given to the work piece and tool remains stationary. In
some other cases, the work piece is stationary and the machine tool provides motion to the cutting tool.
In yet other cases, motion is given both to tool as well as the work piece.
Cutting tools are made of material which can be hardened by suitable heat treatment. During
machining, lot of heat is generated and the temperature of the cutting edge of the tool may reach
650–700°C. The tool must maintain its hardness even at such elevated temperatures. This property of
retaining its hardness at elevated temperatures is called ‘red hardness’. Cutting tools develop the property
of red-hardness due to addition of tungsten and molybdenum to high carbon steel. These days, cutting
tools are made of high speed steel, or tungsten carbide. Tools made of ceramic materials (like Al2O3,
SiC), and polycrystalline diamonds are also used for special applications.
Cutting speed: Readers must understand the concept of “cutting speed”. Cutting speed means
the linear speed at which cutting takes place. If the tool is stationary, the speed at which the work
material approaches the cutting edge of tool is the cutting speed. It is measured in metres per minute.
https://youtu.be/4XfVhlQr_w8
The optimum cutting speed depends upon the tool material, the material to be cut and whether a cutting
fluid is being used or not. The purpose of using cutting fluid is to remove heat from the cutting area and
to lubricate the tool face so that the friction between chip and tool surface reduces. Use of cutting fluid
makes cutting process more efficient. Similarly, cutting at recommended cutting speed results in improved
tool life and performance.
Recommended cutting speed for machining cast iron and mild steel with high speed tools is
35 metres per minute. However, if tungsten carbide tools are used, cutting speeds of 65–70 metres per
minute may be used. For non-ferrous material, much higher cutting speeds are permissible.
CENTRE LATHE
A centre lathe is also called an engine lathe or simply a lathe. It is one of the commonest and oldest
machine tools. It is also one of the most versatile and widely used machines. Its main function is
production of cylindrical profiles.
A centre lathe is shown in
https://www.youtube.com/watch?v=C4orRwqhwNQ
The main parts of a centre lathe are:
1. Machine bed, usually made of cast iron. It holds or supports all other parts of the lathe. The
top of the machine bed is flat and is machined to form guide ways on which the carriage slides along the
length of the lathe
2. Headstock: It is fixed at the extreme left hand of the bed and contains shafts and gears
immersed in lubricating oil. The driving shaft inside is driven by an electric motor. The driven shaft,
which is in the form of a hollow spindle can be driven at various r.p.m. by changing gears, projects out
see this video esey understand
of the headstock, A chuck (either three jaw or four jaw), is screwed on this spindle. The work piece can
be held in the jaws of the chuck. When the spindle rotates, the chuck as well as the work piece held also
rotate about the longitudinal axis of the spindle.
https://youtu.be/Qgmvhnz3w9c
3. Tailstock: A tailstock is provided at the right hand end of the bed. It can slide along the
guide ways provided on the bed and may be brought nearer to the headstock, if so desired. It can then
be clamped or fixed on the bed in that position.
The tailstock has a spindle in the upper part of the tailstock, the axis of which coincides with the
axis of the headstock spindle, both being at the same height above the bed. This spindle can be moved
forwards or backwards by rotating a hand wheel. The front portion of tailstock spindle carries a ‘dead’
different types of pump
or ‘live’ centre. When a long work piece is held in the chuck at the headstock end, it is supported at the
tailstock end by moving forward the tailstock spindle. Of course, there has to be a small conical hole in
the centre of the work piece, in which the tailstock centre may be inserted to provide support. If the
centre (being carried in its own bearings) rotates along with the work piece, it is called a live centre.
However, if the tailstock centre remains stationary and work piece alone rotates, the centre is called
‘dead centre’ and the conical tip of centre has to be lubricated with grease to reduce the friction between
the tailstock centre and the work piece
https://youtu.be/uoFkz9RMeR8
4. Carriage: A carriage is shown in Fig. 1.3. The carriage can slide along the length of the
machine bed from the tailstock end to the head stock end. This movement is controlled by manually
operating the hand traversing wheel. It can also be imparted this traversing motion at different speeds
automatically by engaging into the feed rod or feed shaft.
The carriage carries a cross slide, which can independently move in a crosswise direction at
right angles to the bed. The cross slide can also be moved either manually through a smaller hand wheel
https://youtu.be/uoFkz9RMeR8
or through an automatic device. Mounted upon the cross slide is another small slide, called the compound
rest (or tool post slide) which can be rotated in a horizontal plane. Its normal position at 0°
rotation is parallel to bed. Its angle of rotation can be read off on a protractor. This compound rest is
used during taper turning to set the tool for angular cuts. The compound rest can be moved only manually.
The cutting tool is clamped in the tool post which is mounted on top of the compound rest.
The gears, clutches and other mechanism required for giving movement to the carriage and
cross slide etc. is hidden from view by means of an apron (thin steel plate) screwed upon the front face
of the carriage. Half hidden in the front are two long shafts, (the screwed one is called the lead screw
shaft/rod and the plain one is called feed shaft/rod) extending from the headstock to the tailstock end.
These two shafts can be engaged one at a time to give longitudinal movement to the carriage. Lead
screw is only used during the screw cutting operation. Feed shaft is used in other operations like turning.
Size of a lathe is specified by the distance between headstock chuck to tailstock centre. This is
the length of the longest job which can be accommodated or machined on the lathe. In addition the
swing of the lathe (i.e., the vertical distance between chuck centre and the lathe bed) is specified as this
is the radius of the largest work piece which can be turned on the machine
CUTTING TOOLS USED ON THE LATHE
In a centre lathe, the work piece is held and fastened in a chuck. If a component is manufactured out of
a round bar, the bar passes through the hollow spindle of the headstock, and the required length of bar
is pulled out and then clamped in the jaws of the chuck, free end of the bar projecting towards the
tailstock end. Mostly the movement of tool is from right to left. This is known as right hand working.
Sometimes, it becomes necessary to do some work while moving tools from left to right, i.e., left hand
working. The tools for right hand lathe operations are quite different than tools for left hand working.
In fact they are mirror images of each other.
Many different kind of operations are carried out on lathes
(i) Turning
(ii) Facing
(iii) Taper turning
(iv) Profile turning or form turning
(v) Parting
(vi) Boring
(vii) Threading
(viii) Knurling
Facing
This is usually the first step of any lathe operation on the lathe
machine. The metal is cut from the end to make it fit in the right angle
of the axis and remove the marks.
Tapering
Tapering is to cut the metal to nearly a cone shape with the help of
the compound slide. This is something in between the parallel turning
and facing off. If one is willing to change the angle then they can
adjust the compound slide as they like.
Parallel Turning
This operation is adopted in order to cut the metal parallel to the
axis. Parallel turning is done to decrease the diameter of the metal.
Parting
The part is removed so that it faces the ends. For this the parting
tool is involved in slowly to make perform the operation. For to make
the cut deeper the parting tool is pulled out and transferred to the
side for the cut and to prevent the tool from breaking.
INTRODUCTION
In previous chapters, we have seen that with the help of forging and casting processes, we can manufacture
machine parts of different shapes and sizes. However, parts so manufactured have poor geometry and
size control (i.e., tolerance on dimensions) and their surface finish is not very good. Hence, in most
cases, castings and forgings undergo machining before these parts can be assembled with other parts to
form a complete machine like cycle or motor car etc.
In machining, we use a machine tool like lathe or shaper and a cutting tool made of a much
harder material than the material of the part to be machined. Material removed from the part is achieved
by the relative movement between the cutting tool and the part. The cutting tool is given a sharp cutting
edge and it is forced to penetrate inside the work piece surface to a small depth. The relative motion
between the tool and work piece results in a thin strip of material being sheared off from the work piece
reducing the thickness of the work piece. This process has to be repeated several times before the entire
surface of the work piece can be covered and reduced in depth. The thin strip of the material sheared
from the work piece is called ‘chip’. It must be understood that chips are produced by shearing action
and not by cutting. Subtantial amount of power is required for machining. The function of the machine
tool is to provide this power and the required motion of work piece relative to the tool.
In some cases of machining, motion is given to the work piece and tool remains stationary. In
some other cases, the work piece is stationary and the machine tool provides motion to the cutting tool.
In yet other cases, motion is given both to tool as well as the work piece.
Cutting tools are made of material which can be hardened by suitable heat treatment. During
machining, lot of heat is generated and the temperature of the cutting edge of the tool may reach
650–700°C. The tool must maintain its hardness even at such elevated temperatures. This property of
retaining its hardness at elevated temperatures is called ‘red hardness’. Cutting tools develop the property
of red-hardness due to addition of tungsten and molybdenum to high carbon steel. These days, cutting
tools are made of high speed steel, or tungsten carbide. Tools made of ceramic materials (like Al2O3,
SiC), and polycrystalline diamonds are also used for special applications.
Cutting speed: Readers must understand the concept of “cutting speed”. Cutting speed means
the linear speed at which cutting takes place. If the tool is stationary, the speed at which the work
material approaches the cutting edge of tool is the cutting speed. It is measured in metres per minute.
https://youtu.be/4XfVhlQr_w8
The optimum cutting speed depends upon the tool material, the material to be cut and whether a cutting
fluid is being used or not. The purpose of using cutting fluid is to remove heat from the cutting area and
to lubricate the tool face so that the friction between chip and tool surface reduces. Use of cutting fluid
makes cutting process more efficient. Similarly, cutting at recommended cutting speed results in improved
tool life and performance.
Recommended cutting speed for machining cast iron and mild steel with high speed tools is
35 metres per minute. However, if tungsten carbide tools are used, cutting speeds of 65–70 metres per
minute may be used. For non-ferrous material, much higher cutting speeds are permissible.
CENTRE LATHE
A centre lathe is also called an engine lathe or simply a lathe. It is one of the commonest and oldest
machine tools. It is also one of the most versatile and widely used machines. Its main function is
production of cylindrical profiles.
A centre lathe is shown in
The main parts of a centre lathe are:
1. Machine bed, usually made of cast iron. It holds or supports all other parts of the lathe. The
top of the machine bed is flat and is machined to form guide ways on which the carriage slides along the
length of the lathe
2. Headstock: It is fixed at the extreme left hand of the bed and contains shafts and gears
immersed in lubricating oil. The driving shaft inside is driven by an electric motor. The driven shaft,
which is in the form of a hollow spindle can be driven at various r.p.m. by changing gears, projects out
see this video esey understand
of the headstock, A chuck (either three jaw or four jaw), is screwed on this spindle. The work piece can
be held in the jaws of the chuck. When the spindle rotates, the chuck as well as the work piece held also
rotate about the longitudinal axis of the spindle.
https://youtu.be/Qgmvhnz3w9c
3. Tailstock: A tailstock is provided at the right hand end of the bed. It can slide along the
guide ways provided on the bed and may be brought nearer to the headstock, if so desired. It can then
be clamped or fixed on the bed in that position.
The tailstock has a spindle in the upper part of the tailstock, the axis of which coincides with the
axis of the headstock spindle, both being at the same height above the bed. This spindle can be moved
forwards or backwards by rotating a hand wheel. The front portion of tailstock spindle carries a ‘dead’
different types of pump
or ‘live’ centre. When a long work piece is held in the chuck at the headstock end, it is supported at the
tailstock end by moving forward the tailstock spindle. Of course, there has to be a small conical hole in
the centre of the work piece, in which the tailstock centre may be inserted to provide support. If the
centre (being carried in its own bearings) rotates along with the work piece, it is called a live centre.
However, if the tailstock centre remains stationary and work piece alone rotates, the centre is called
‘dead centre’ and the conical tip of centre has to be lubricated with grease to reduce the friction between
the tailstock centre and the work piece
4. Carriage: A carriage is shown in Fig. 1.3. The carriage can slide along the length of the
machine bed from the tailstock end to the head stock end. This movement is controlled by manually
operating the hand traversing wheel. It can also be imparted this traversing motion at different speeds
automatically by engaging into the feed rod or feed shaft.
The carriage carries a cross slide, which can independently move in a crosswise direction at
right angles to the bed. The cross slide can also be moved either manually through a smaller hand wheel
https://youtu.be/uoFkz9RMeR8
or through an automatic device. Mounted upon the cross slide is another small slide, called the compound
rest (or tool post slide) which can be rotated in a horizontal plane. Its normal position at 0°
rotation is parallel to bed. Its angle of rotation can be read off on a protractor. This compound rest is
used during taper turning to set the tool for angular cuts. The compound rest can be moved only manually.
The cutting tool is clamped in the tool post which is mounted on top of the compound rest.
The gears, clutches and other mechanism required for giving movement to the carriage and
cross slide etc. is hidden from view by means of an apron (thin steel plate) screwed upon the front face
of the carriage. Half hidden in the front are two long shafts, (the screwed one is called the lead screw
shaft/rod and the plain one is called feed shaft/rod) extending from the headstock to the tailstock end.
These two shafts can be engaged one at a time to give longitudinal movement to the carriage. Lead
screw is only used during the screw cutting operation. Feed shaft is used in other operations like turning.
Size of a lathe is specified by the distance between headstock chuck to tailstock centre. This is
the length of the longest job which can be accommodated or machined on the lathe. In addition the
swing of the lathe (i.e., the vertical distance between chuck centre and the lathe bed) is specified as this
is the radius of the largest work piece which can be turned on the machine
CUTTING TOOLS USED ON THE LATHE
In a centre lathe, the work piece is held and fastened in a chuck. If a component is manufactured out of
a round bar, the bar passes through the hollow spindle of the headstock, and the required length of bar
is pulled out and then clamped in the jaws of the chuck, free end of the bar projecting towards the
tailstock end. Mostly the movement of tool is from right to left. This is known as right hand working.
Sometimes, it becomes necessary to do some work while moving tools from left to right, i.e., left hand
working. The tools for right hand lathe operations are quite different than tools for left hand working.
In fact they are mirror images of each other.
Many different kind of operations are carried out on lathes
(i) Turning
(ii) Facing
(iii) Taper turning
(iv) Profile turning or form turning
(v) Parting
(vi) Boring
(vii) Threading
(viii) Knurling
Facing
This is usually the first step of any lathe operation on the lathe
machine. The metal is cut from the end to make it fit in the right angle
of the axis and remove the marks.
Tapering
Tapering is to cut the metal to nearly a cone shape with the help of
the compound slide. This is something in between the parallel turning
and facing off. If one is willing to change the angle then they can
adjust the compound slide as they like.
Parallel Turning
This operation is adopted in order to cut the metal parallel to the
axis. Parallel turning is done to decrease the diameter of the metal.
Parting
Click Here!
The part is removed so that it faces the ends. For this the parting
tool is involved in slowly to make perform the operation. For to make
the cut deeper the parting tool is pulled out and transferred to the
side for the cut and to prevent the tool from breaking.
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Other Recommended Mobile Phones:- Less Than 5000
Less Than 5000 - 10,000
Less Than 15000
Less than 30000
More Then products
Recommended Earphones Under 999
Top Smartphone of 2017
My YouTube Gears -
flipkart .....................................
👌👌
Other Recommended Mobile Phones:- Less Than 5000
Less Than 5000 - 10,000
Less Than 15000
Less than 30000
More Then products
Recommended Earphones Under 999
Top Smartphone of 2017
My YouTube Gears -
flipkart .....................................
👌👌
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