Capstan lathe is a modified form of metal lathe ideal for mass-production applications where high accuracy with quick cycle time is of importance.
These lathes are best suitable for lightweight machining of relatively small workpieces.
But what exactly is a Capstan lathe, and is it suitable for your application?
This article discusses Capstan lathes in detail by going through its physical features, working, and applications.
In the end, I've also compared capstan lathes with turret lathes to help you choose the appropriate lathe for your application.
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What is a Capstan Lathe?
A capstan lathe is a variant of typical metal lathes and consists of a turret capable of holding six different cutting tools to perform various operations in a single go. This overcomes the limitation of long downtime for tool change on traditional lathes, thereby enhancing the productivity of the machine.
Its hexagon-shaped turret follows an intermittent tool change method, called the Geneva mechanism.
The ability to switch between six different cutting tools during the matching process reduces the cycle time for producing complex objects that require multiple machining operations.
Furthermore, quick tool change reduces the cycle time, making it ideal for mass production applications.
The hexagonal turret in a Capstan lathe is mounted on a ram that moves along the Z-axis to provide feed to the cutting tool.
A typical capstan lathe has a semi-automatic mode of operation. It means that, although the machining processes can be automated, functions like tool indexing and workpiece clamping are manual.
On the contrary, in computer numerical control (CNC) capstan lathes, all operations are automatic, ranging from machining operations to tool change or switching coolant supply on/off.
Parts of a Capstan Lathe
Capstan lathe is a type of metal lathe and therefore consists of all the basic parts of a lathe machine with certain modifications that enhance its functionality.
A turret is a tool holder supported by a rotary bearing, enabling it to rotate about its vertical axis.
Its shape can be hexagonal, square, or circular. It is attached to the ram that sits on the saddle. Each side of the turret has tapped holes to cater to the adjustment of tools.
Usually, the turret accommodates up to six tools, and for indexing a specific tool, the handwheel connected to the turret is rotated in the counterclockwise direction.
The ram can only slide along the horizontal axis to provide feed to the turret, which consequently moves the tool.
For instance, two different cutting tools will be required to perform turning followed by drilling operation on a mild steel cylinder.
The cutting tool attached to the tool post will perform the turning operation, whereas the drill bit attached to the turret will perform drilling, simultaneously.
To execute a different process, the desired tool can be indexed from the turret, either using a handwheel or CNC automation.
This enhances productivity by reducing the tool change time during a machining operation.
The headstock is a rigid, cast iron structure containing all the control options of the lathe, such as start, stop, and speed control. It regulates the driving mechanisms that include gears, pulleys, or motors.
A headstock spindle of a Capstan lathe houses a collet chuck, which holds the workpiece firmly during the machining operation. The spindle RPM is usually in the range of 500 to 2000 RPM.
The headstock has two categories based on the drive system employed: electric headstock and geared headstock.
An electric headstock achieves spindle speed control by directly varying the RPM of the electric motor.
It enables better speed control at the expense of torque and is common in lathes where smaller workpieces are machined.
On the contrary, geared headstocks consist of a gearbox configuration to achieve spindle speed control.
This mechanism lowers the spindle speed while increasing its torque and vice versa.
Thus, making it ideal for machining larger workpieces and performing deep cuts in harder materials.
A lathe bed is a cast iron or mild steel platform that houses all the components of a capstan lathe, such as cross-slide, headstock, and toolpost.
It also provides the ability to slide the saddle along the axis of the lathe to perform the desired machining operation.
A tool post, usually square-shaped, houses all the cutting tools. It provides the ability to set the height of the cutting tool. However, the height cannot be adjusted during the machining operation.
The toolpost sits on a structure known as a compound, that facilitates longitudinal movement of the cutting tool, by rotating the handwheel.
Apart from the longitudinal movement, the cutting tool can also be moved radially along the X-axis with the help of the cross slide.
For semi-automatic lathes, handwheels can be rotated manually to move the tool post, while in CNC lathes, this motion is automated.
Cross-slide houses the tool post and provides the ability to move the cutting tool along the X-axis of the lathe, perpendicular to the movement of the saddle.
This movement of the cutting tool is used for machining the workpiece along its diameter.
The driving clutch connects and disconnects the driver (prime mover/motor) from the spindle.
It functions similar to that of the clutch used in automobiles.
Before initiating the machining operation, the prime mover and the spindle are coupled by engaging the clutch.
Similarly, after the completion of the process, they are decoupled by disengaging the clutch.
Working of a Capstan Lathe
There is a series of steps you need to follow for using a capstan lathe.
Insert the workpiece in the collet chuck and fasten the required tools onto the turret and the tool post, using a wrench.
Switch on the main power supply and start the prime mover. Engage the clutch to couple the prime mover with the spindle to rotate the workpiece.
After mounting the tools in the turret, move it towards the workpiece by sliding the ram that sits on the saddle.
It must be noted that, generally, the turret can only be moved along the Z-axis and, therefore, can be used for performing operations like drilling, tapering, or boring.
If multiple operations are required, they can be sequentially performed by moving the turret away from the workpiece after each successful operation, indexing the required tool, and again bringing the tool in contact with the workpiece.
Capstan lathes consist of a tool post and a turret, making it possible to perform two machining operations simultaneously.
The cross slide enables the cutting tool to move sideways with respect to the plane of rotation, while the compound handwheel moves the tool post longitudinally.
In this way, you can perform a turning operation on the surface of the blank as per requirement.
Once you finalize your workpiece, move the tool post away, disengage the clutch, and stop the prime mover before switching off the main power supply.
Use a wrench to loosen the collet to remove the workpiece and the tools from the turret and tool post.
Inspect the quality of the workpiece and, if needed, use a hand file to smoothen the edges.
Ensure that you always follow safety protocols, wear safety goggles, safety shoes, a safety jacket, and safety headgear.
It must be ensured that the power supply is off before mounting the workpiece or removing it from the collet.
Maintain a safe distance during machine operation. Ideally, install a safety enclosure on the lathe to reduce the risk of injury from hot chips removed during the machining operation.
Applications of Capstan lathes
Capstan lathes are versatile lathes that can be used for performing various operations like turning, boring, drilling, threading, reaming, chamfering, parting, grooving, etc.
The ability to switch the cutting tool during the machining process increases productivity by reducing the cycle time, thereby making Capstan lathes ideal for batch and mass production applications.
These lathes are ideal for repetitive jobs, such as manufacturing a hex-nut, which requires frequent tool changes to perform boring and tapping operations.
The ability to index the turret and switch the cutting tool reduces the production time and increases the throughput for such applications.
Capstan lathes are lightweight and relatively small in size, which adds to their portability and practicality in small and medium-scale manufacturing industries.
They are ideal for machining small workpieces requiring greater accuracy and complex geometries.
Moreover, the components of capstan lathes have sufficient rigidity and strength to withstand fatigue loading or heavy loads to an acceptable limit.
The operating procedure of a capstan lathe is simple, making it easy to use and eliminating the need for an expert operator.
Based on the applications and machining processes, capstan lathes have great potential in metalworking, metal spinning, thermal spraying, part restoration, and glass-working industries.
Apart from that, these lathes can also be used for simple woodworking applications like turning vases.
Difference Between a Capstan Lathe and Turret Lathe
|Parameters||Capstan lathe||Turret lathe|
|Workpiece size||Small (up to 60mm in diameter)||Large (up to 120mm in diameter)|
|Speed of operation||Fast||Slow|
|Feed motion||Ram is moved||Saddle is moved|
|Arrangement||Only horizontal||Horizontal and vertical|
|Turret shape||Hexagonal, square, or circular||Hexagonal|
|Turret mounting base||Ram, which is mounted on a saddle||Directly on saddle|
|Workpiece mounting||Collet||Jaw chuck|
|Nature of cuts||Light to medium cuts due to relatively lower rigidity||Heavy cuts due to higher rigidity|
|Indexing turret||The handwheel of the ram is rotated||Turret rotated manually after releasing the clamping lever|
Difference between Capstan lathe and Turret lathe
Capstan lathes are light in weight and therefore offer comparatively less rigidity, making them ideal for working on smaller workpieces where light cuts with a quick cycle time are required.
Whereas turret lathes offer rigid construction, ideal for performing heavy cuts. However, the manual indexing of the turret slightly increases the cycle time.
In capstan lathes, the ram slides over the saddle to move the tool. This restricts the motion of the tool, thereby limiting the length of the stock that can be machined.
On the contrary, in turret lathes, the whole saddle can slide over the guideways, enabling a broader range of motion which means that a greater length of the stock can be machined.
Some turret lathes offer flexibility to move the turret head along the X-axis, enhancing their functionality. However, this movement is not possible in Capstan lathes.
Capstan lathes provide enhanced functionality and faster tool change during the machining operation, giving them an edge over conventional lathes.
Despite their enhanced functionality, these lathes are easy to use and can be operated by a skillful individual familiar with lathe operations.
Therefore, Capstan lathes are ideal for large-scale production applications, where quick speed and smooth surface finish are of importance.
Generally, these lathes are best suitable for light machining operations on soft metals. However, if working with hard metals is your primary requirement, a turret lathe would be an ideal choice.
Frequently Asked Questions (FAQ)
Can we adjust the height of the turret?
No, the height of the turret is fixed and aligned with the axis of the spindle. However, some turret lathes provide the ability to adjust the position of the turret along the X-axis, which cannot be found in capstan lathes.
What makes capstan lathes different from engine lathes?
Capstan lathes can accommodate up to six different tools in their turret, at a single time. On the contrary, conventional/engine lathes house a single tool attached to the tool post. If a different tool is required, the previous tool is removed, and the new one is mounted onto the tool post. So, capstan lathes have higher productivity.
Can we use a capstan lathe to machine wood and other non-metals?
Yes, capstan lathes can be employed for machining wood and non-metals like glass. It is due to the fact that these lathes provide variable speed control for performing smooth cuts on different workpieces with high accuracy.