Capstan Lathe – Parts, Construction, Working and Advantages

Capstan Lathe is the modified form of Engine Lathe and Center Lathe in which the tailstock is replaced by a hexagonal turret tool head. It was first developed by Pratt and Whitney in America in 1860.

It was needed to develop capstan lathe because in center lathe there was only one tool post and only one tool can be fitted in the tailstock. So it was very time consuming for every time we have to change the tool while changing the operation to be performed on the workpiece. Center lathe was not suitable for mass production.
To overcome these problems capstan lathe was developed. Capstan lathe is a modified form of the center lathe.

This turret tool head has 6 different types of tools. The turret tool is rotated to get the required tool for the operation.
It is used in mass production i.e to produce a large number of final products in very less time with maximum accuracy and precision.

It is a semi-automatic lathe. It is called semi-automatic because the machining processes like drilling, facing, thread cutting, turning, etc are done automatically without changing the tools but other works like workpiece clamping, setting tools and cooling are done manually.

Parts of Capstan Lathe:-

1 Bed:
This bed is made by casting. All other parts of lathe machine is bolted on it. Small beds are made by casting directly and if big bed is to be made then two beds are mady through casting and these two beds are joined using bolts. This made is made up of cast iron.

2 Legs:
There are two legs in the lathe. These two legs support the lathe. These legs are also made up of cast iron.

3 Feed Rod:
The carriage move over this feed rod. This feed road has threads.

4 Head Stock:
Head Stock is present over the bed. It is a chamber with all the driving mechanisms inside it. This driving mechanism can contain gears, pulleys or motors.

5 Chuck:
This chuck is of two types. One is three jaw chuck and another one is four jaw chuck. Three jaw chuck is a universal chuck. Its main work is to hold the workpiece.

6 Guideways:
There are guideways on the bed over which the carriage and cross-slide moves.

7 Saddle:
This saddle slides along the bed way and support the cross-slide, compound rest and tool post.

8 Cross-slide:
Cross-slide moves cross in the direction perpendicular to the movement of the ram.

9 Tool Post:
It is present over the saddle. There are two tool post which can als move cross i.e in direction perpendicular to the direction of movement of saddle.

Instead of tail stock there are certain parts present in capstan lathe which are:-

i) Saddle :- This saddle can move left and right. It carries ram and hexagonal tool head with it. It is used to take the ram and hexagonal tool head near the workpiece.
ii) Ram :- Ram can also move left and right. It carries hexagonal tool head and is used for shorter movements of tool after the saddle is fixed in its position.
iii)Hexagonal tool post Or turret head:- It is present over the ram.It can hold six faces which can hold six different types of machining tools for various operations.
iv) Hand Wheel :- This hand wheel is used to move the saddle along with the ram and hexagonal tool head.

Construction:

Two legs support the complete structure of the lathe. Above the legs bed is present.
There is a feed rod present above the bed over which the saddle of tool post and saddle of hexagonal tool head moves.
On the left side head stock is present which contains all the driving mechanisms inside it. The head stock has a spindle at the end of which a chuck is attached which rotates with the spindle.
Apart from this, two saddle are present over the feed rod. One saddle has two tool post and other saddle has a ram over which the hexagonal tool head is present.
The hexagonal tool head has 6 faces and 6 diiferent machining tools can be attached to this hexagonal tool head for different operatons.

Instead of tail stock, a hexagonal tool head is used in capstan lathe. It is a lightweight machine.
Feed is provided to the tool by moving the ram. Because of no saddle displacement, the movement of the turret tool head in the longitudinal direction of the bed is small along the ram.
This capstan lathe is used for working on shorter workpieces because of limited ram movement. Its operation is fast because of lighter in constructions.

Working:

In capstan lathe, there are six tools available in the hexagonal tool post. At first, the workpiece which is to be changed into a desired shape and size is inserted in the chuck.
This chuck can be three-jaw or four-jaw chuck. This workpiece rotates as the chuck rotates which is connected to a spindle.

There are six different faces in the hexagonal tool head to hold six different types of tools.
When the workpiece starts rotating with the chuck, the hexagonal tool head is moved towards the workpiece by moving the saddle. This hexagonal tool head can rotate and by rotating it, the required tool for operation is faced towards the workpiece.
After the required tool is faced towards the workpiece, the tool is brought into contact with the workpiece by moving the ram forward and the required operation is done.
After the first operation is finished and the ram is moved backward, the turret indexes automatically and the tool mounted on the next face comes into operation.

Advantages:

1) It can be used for mass production as production rate is high.
2) Different ranges of speed can be used.
3) Multiple tools can be accommodated at the same time.
4) It has a high rigidity.

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