The Lathe: Function of Lathe, Types of Lathe


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The
Lathe:-
·       
The Lathe is one of the most versatile
and widely used machine tools all over the world. It is commonly
known as the mother of all the machine tool.
·       
In the year
1797 Henry Maudslay, an Englishman, designed the first screw
cutting lathe which is
forerunner of the present day high speed, heavy duty production lathe, a
machine tool which has practically given shape to our present day by building
machines and industries.

Function
of Lathe:-
·   The main function of lathe is to remove
material from the workpiece to give it the required shape and size.
·       
This is accomplished by holding the
workpiece securely on the machine and then turning it against the tool which
will remove the material from the workpiece.
·       
To cut the
material properly the tool should be harder than the workpiece material, should be rigidly held on the machine and should be fed in a definite
way relative to the
workpiece.

Types
of Lathe:-
Lathes are manufactured in a variety of
types and sizes, from very small bench lathes used for precision work
to huge lathes
used for turning
large steel shafts.
But the principle of operation
and function of all types of lathes
is same.
    
The different types of lathes
are:
1.               
Speed Lathe                             3.     Bench lathe
A.               
Wood
working              4.     Tool room
lathe
B.               
Centering                      5.     Capstan
& Turret lathe
C.              
Polishing                       6.      Special
purpose lathe
D.              
spinning                                A.  Wheel lathe
2.               
Engine
Lathe                                   B.  Gap bed lathe
A.               
Belt
drive                               C.  T – lathe
B.               
Individual motor drive           D.  Duplicating lathe
C.              
Gear
drive                      7.     Automatic
lathe


Speed lathe
·       
Speed
lathe is the simplest type of lathe.
It consists of bed, headstock, tailstock and tool post. There is no feed box, lead screw or carriage.
·       
Tool
is mounted on the tool post and is fed into work purely by hand control. Due to this characteristic of lathe enables
the designer to give high
speeds range from
1200 to 3600 r.p.m.
·       
The headstock construction is very simple
and only two
or three speeds
are available.
·       
The “speed lathe”
has been so named because
of the very high speed of the spindle
speed. It is mainly used for wood working, spinning, centering and
polishing etc.
Engine lathe
·       
It is the most common
types of lathe and is widely used in workshop.
·       
Similar to the speed lathe, the engine
lathe has got all the basic parts, e.g. bed, headstock and tailstock. But the headstock of an engine
lathe is much
more robust in construction and it contains
mechanism for multiple
speeds.
·       
The cutting tool may be fed both in cross
and longitudinal direction
with reference to the lathe axis with the help of carriage.
·       
Engine lathes are classified according
to the method of power transmission to the machine.

Bench lathe 
·       
It is usually
mounted on a bench.
·       
It has practically all the parts of an engine lathe and it performs all the operations, its only difference being
in the size. This is used for small and precise work.
Tool
room lathe
·       
A tool room
lathe having features
similar to an engine lathe and is much more
accurate and has wide range of speed from vary low to 2500 r.p.m.
·       
It is used for manufacturing precision components, dies,
tools, jigs etc. and hence
it is called as tool rom lathe.

Capstan & Turret lathe
·       
These
lathes have provision to hold a number of tools and can be used for
performing wider range of operations.
·       
These
are particularly suitable for mass production of identical parts
in minimum time.

Special
purpose lathe
·       
They
are used for special purposes
and for jobs which cannot
be accommodated or conveniently machined on a standard lathe.
·       
Wheel
lathe is used
to produce locomotive wheels.
·       
Gap bed lathe
is used for machining extra-large diameter workpiece.
·       
T Lathe is used for machining of rotors for jet engines.
·       
Duplicating lathe is used for
duplicating the shape of a flat or round template on to the workpiece.

·   
Automatic lathe
·   
These
are high speed,
heavy duty, mass production lathes
with complete automatic control. Once the tools are set
and the machine is started it performs all the operations to finish the job.
·      
The changing of tools, speeds
and feeds are also done automatically.
Size
of Lathe
·       
The size of a lathe
is expressed by the following items and shown
in Fig

·       
The height of the center measured from the lathe bed.
·       
The swing diameter over bed is the
largest diameter of workpiece that will revolve without touching the bed and is twice the height
of the center measured from the bed of the lathe.

·       
The length between center is the
maximum length of the workpiece that can be mounted between two centres.
·       
The swing diameter over carriage is the largest diameter of workpiece that will
revolve over the saddle, and is always
less than the swing diameter
over bed.
·       
The maximum bar diameter is the maximum
diameter of bar stock that will pass through
hole of the headstock spindle.

·       
The length of bed indicates the approximate floor
space occupied by the lathe.
·       
Other important particulars to specify
the lathe are width of the bed, depth of the bed, depth and width
of gap if gap bed lathe, swing
over gap. Spindle
nose diameter, center taper,
Morse number and range of spindle speeds,
number of feeds pitch of lead screw etc.

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