Capstan and Turret Lathe:

A capstan and turret lathe is a production lathe. It is used to manufacture any number of identical pieces in the minimum time.

These lathes were first developed in the United States of America by Pratt and Whitney in 1960.

Capstan lathe is one of the types of semi-automatic lathe.

In semi-automatic lathes machining operations are done automatically.

Functions other than machining like loading and unloading of a job, the positioning of tools coolant operations are done manually.

The turret head is mounted on the ram fitted with turret slides longitudinally on the saddle.

Turret head has a hexagonal block having six faces with a bore for mounting six or more than six tools at a time.

The threaded hole on these faces is used to hold the tools.

In the case of a Capstan Lathe, the hexagonal turret is mounted on a short slide or ram which again fitted with a saddle.

The saddle can be move accordingly throughout the bed ways and can be fixed to the bed if necessary.

It is specially used for bar type jobs.

But in the case of Turret Lathe, the hexagonal turret directly mounted on the saddle. The saddle can be move through the bed ways.

Turret lathe is generally used for chucking type work.

Schematic Diagram of a Capstan Lathe:

Schematic Diagram of a Turret Lathe:

Capstan and Turret Lathe Working:

The workpiece is held in collet or chucks which are actuated hydraulically or pneumatically.

All the needed tools are held in the respective holes on the turret head.

According to the sequence of operation, the tool is moved with the help of a turret head.

Drilling, boring, turning, reaming, threading tools are mounted on the turret head.

Forming, chamfering, knurling tools are mounted on the front end of the turret.

The Parting tool is mounted in an inverted position on the rear end of the turret.

After completing each operation the turret head is moved back to its initial position which indexes the tools automatically.

Capstan and Turret Lathe Advantages:

The advantages of Capstan and Turret Lathe is the following:

• The rate of production is higher
• Different ranges of speeds are obtained.
• A number of tools can be accommodated.
• Chucking of larger workpieces can be done.
• Operators of less skill are required hence lowers the labor cost.
• Higher rigidity so can withstand heavy loads.

Bar Feeding Mechanism in Capstan and Turret Lathe:

In the bar feeding mechanism, the bar is pushed after the chuck is released without stopping the Lathe Machine.

We use this mechanism for minimizing the setting time.

The bar is passed through the pedestal bushing, bar holding chuck, headstock spindle, and the collet chuck.

The collet chuck is screwed on the headstock spindle and holding the feed bar and also helps the bar to rotates as per spindle speed.

Bar holding chuck rotates within the sliding block with the rotation of the feeding bar.

Also, you can see a rope and a deadweight in this mechanism.

One side of the rope is attached with the sliding block with the help of pin and another side of rope passes through 2 different pulleys and then connecting with a deadweight at its end.

So now when the collet chuck released by the lever the dead weight tends to move in the downward direction, due to this it exerts thrust on the bar holding chuck and feed the bar until it touches the workshop.

As we already have seen that Capstan Lathe is best for bar types jobs that’s why we are generally seeing Bar Feeding Mechanism on Capstan Lathe.

Tools used in Capstan and Turret Lathe:

Collect Chuck:

This is used for griping or you can holding any small bars in Capstan and Turret Lathe (Mainly when we do Mass production).

The size of collet chucks is different corresponding to the bar sizes.

The jaws of the collet chuck are gripped the workpiece by its springing nature.

It is a thin steel brass bushing having slots on the outer side throughout its length.

Roller Box Steady Turning Tool:

This type of tool is used on bar work and when a considerable amount of stock is to be removed from the job.

Roller box consists of the backrest or traveling two roller steadies that can be adjusted as per requirement.

A single point cutting tool is present in front of two rollers and gives rigidity to the workpiece.

Due to this rigid support, depth of cut, turning, etc. can be performed very smoothly.

This is a costly tool only used in mass production.

Self-opening Die Head:

This tool is used especially for cutting external threads.

The pitch of the cutting edges is determined according to the required thread pitch to be cut.

Chasers may be triangular, tangential, and circular types.

The function of the self-opening die is it opened automatically when the tool travel is stopped after the screw cutting operation.

Difference Between Capstan and Turret Lathe Machine:

Capstan Lathe	Turret Lathe
In capstan lathe, the turret tool head is mounted over the ram and that is mounted over the saddle.	In turret lathe, the turret tool head is mounted over the saddle like a single unit.
For providing feed to the tool, ram is moved.	For providing feed to the tool, a saddle is moved.
Capstan lathe is a Lightweight machine.	Turret Lathe is a Lightweight machine.
The turret head cannot be moved in the lateral direction of the bed.	The turret head can be moved crosswise i.e. in the lateral direction of bed in some turret lathe.
In capstan lathe, the collet is used to gripping the Job.	In turret lathe, power Jaw chuck is used to gripping the Job.
Capstan lathe is usually horizontal lathes.	Turret lathes are available in horizontal and vertical lathes.
Because of no saddle displacement, Movement of turret tool head over the longitudinal direction of bed is small along with the ram.	Turret tool head moves along with the saddle over the entire bed in the longitudinal direction.
For indexing turret tool head, the handwheel of the ram is reversed and turret tool index automatically.	For indexing turret tool head, a turret is rotated manually after releasing clamping lever.
Capstan lathe working operations are faster because of lighter in construction.	Turret lathe working operations are slower because of heavier in constructions.
Capstan lathe used for shorter workpiece because of limited ram movement.	Turret lathe used for longer workpiece because of saddle movement along the bed.
In Capstan lathe used for machining workpiece up to 60 mm diameter.	In Turret lathe used for machining workpiece up to 120 mm in diameter.
Heavy cuts on the workpiece cannot be given because of non-rigid construction.	Heavy cuts on the workpiece can be given because of the rigid construction of the machine.

Let’s see the difference between Capstan and Turret Lathe from the Engine Lathe:

ENGINE LATHE	CAPSTAN AND TURRET LATHE
The direction of rotation is mostly anti-clockwise	It can rotate in both directions.
Required less power as these machines are design for doing a single operation at a time.	Requied 4-5 times more power because of handaling 2-3 operations at a time.
Less number of spindle speed available in these types of lathe	The vast amount of spindle speeds are available
Setting and machining time is higher.	Setting and machining time for mass production is very less, as its handle sevaral operation at a time.
The skilled operator needed.	Semi-skilled operators can be run the machine
The lead screw present in these types of lathe is long	Lead screw is not present but short threads can be easily cut by chaser.
Any type of taper turning can be done by this machine	Only short length taper can be done with the help of the form tool.

Summary:

Conclusion:

As we saw in this article that these machines are the modification of an Engine Lath, also there is no long lead screw in this type of lathe.

Capstan and turret lathes are now used vastly in the Manufacturing tool to produce mass products.

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References:

• Capstan and Turret Lathe Work
• Turret Lathe on Wiki
• A textbook of manufacturing technology: Manufacturing processes
• Manufacturing by NTPEL