What is a Lathe? How does it Work

Lathes are one of the most widely used machining tools that provide the flexibility to perform various machining operations on a single machine.

These machines are available in different sizes and have different machining capabilities.

Therefore, it is important to understand the functionality and study the various parameters of a lathe before buying one.

This article will provide a comprehensive guide on lathe machines and shed some light on their features, types, and machining operations.

In the end, this article will also talk about the things you should consider when buying a lathe.

What is a Lathe?

Lathe is a machine consisting of a spindle that rotates the workpiece at high speed while the cutting tool moves along the X-Z plane to remove the material and perform various machining operations like turning, knurling, boring, threading, facing, etc. It is generally used to create axisymmetrical parts.

It is one of the oldest tools that finds a place in almost every machine shop.

Traditional lathes have a 2-axis system in which the tool can be positioned at the front/back of the workpiece along the X-axis and left/right along the Z-axis.

However, modern CNC lathe axis systems can consist of 3, 4, or 5 axes, making them ideal for machining complex geometries with quick cycle time.

Parts of a Lathe

A lathe consists of various parts that function in coordination to perform different machining operations.

Bed

Bed is the main part of a lathe that houses all the other parts on it.

Generally, the bed size determines the maximum length of the workpiece that a lathe can handle.

Headstock

Headstock is the work-holding part of a lathe that houses the spindle, chuck, gear-drive, and automatic controls such as speed and feed control levers.

It is the stationary element of lathe that has no relative movement with respect to the chassis and is generally located on the left-hand side of the lathe.

The headstock also houses spindle speed control levers that can be used to toggle between low and high RPM of the spindle.

Tailstock

Tailstock is located on the right of the lathe and is used for holding long workpieces.

It can be moved left and right on the guideways along the Z-axis to hold workpieces of variable lengths.

However, it is not used during the machining of small workpieces.

Toolpost

Toolpost holds the cutting tool and is generally located on the carriage, between the tailstock and headstock.

The cross slide helps in positioning the tool post along X-axis, whereas the feed rod facilitates movement along Z-axis.

Therefore, the combined movement of the cross slide and lead screw provides transmission of the cutting tool in the XZ plane.

Lead Screw

Lead screw guides the longitudinal movement of the carriage. Its function is similar to the feed rod but is normally used during the automation of tool feed.

The automatic tool feed is generally used during the finishing and threading processes.

Spindle

Spindle is the rotating part of the lathe that spins the workpiece at high RPM.

It is driven by the spindle motor, connected through a belt drive or direct drive system.

Chuck

Chuck is mounted on the spindle and is used for holding the workpiece.

A typical chuck consists of 3 jaws or 4 jaws that are individually adjusted, by using a chuck-key, to hold the workpiece in line with the axis of the lathe.

In lathe machining, the alignment of the workpiece plays an important role in the quality of the final product, and even a single-degree offset can ruin the job. 

Therefore, a dial indicator is used to check the concentricity of the workpiece and have it perfectly aligned with the longitudinal axis of the lathe.

Handle Wheels 

There are generally three handle wheels on a lathe machine.

These wheels are used to move the tool post, carriage, and tailstock around the work area of the lathe.

Handle wheels are used for manually controlling the movements of these elements along the X and Z-axis.

Servo Motor for Automatic Feed

Servo motor is used for driving the lead screw to set the automatic tool feed.

This motor controls the movement of the tool according to the feed and depth of cut parameters set by the operator using the automatic control levers.

Cutting Tool

The cutting tool is mounted on the tool post and is used for removing the material from the stock.

There are various types of lathe cutting tools that can be used for performing different machining operations on a lathe.

Apart from all these components, most metal lathes also consist of mist or flood-type cutting fluid delivery system.

Types of Lathes

Apart from differentiating lathes on the basis of their size (mini, midi, and full-size), lathes are classified on the basis of their structure and functionality.

Engine Lathe or Center Lathe

These are one of the oldest lathes used for machining sheet metal and were originally driven by a steam engine, thus the name Engine lathe.

It is a horizontal machining tool that is primarily used for performing various machining operations on metals, such as turning, facing, knurling, etc.

Engine lathes are one of the most versatile lathes that are used for making metal parts for automobiles, fabrication, etc.

In this lathe, the tool is mounted on the tool post and can be moved laterally (along X-axis) and longitudinally (along Z-axis) to perform the desired machining process.

Toolroom Lathe 

A toolroom lathe is a modified engine lathe that provides higher precision and accuracy in machining operations.

These lathes are generally used for industrial applications where highly precise taper turning, threading, or grinding of a workpiece is desired.

Toolroom lathes have a comparatively smaller bed size than standard engine lathes. A gunsmith lathe is an example of a toolroom lathe.

Capstan and Turret Lathes

Capstan and Turrent lathes are yet another modification of the engine lathe and are used for large-scale machining operations where high-volume production with quick cycle time is desirable.

In these lathes, the tail stock is replaced with a hexagonal turret that holds multiple machine tools and can perform different machining operations in one go.

Capstan and turret lathes have similar functionality, with the major difference being that turret lathes can handle heavy-duty machining operations, whereas capstan lathes are ideal for lightweight operations.

Speed lathe

Speed lathes, as the name suggests, are high-speed lathes that are comparatively less powerful than engine lathes but have a higher turning speed (1200–3600 RPM).

In these lathes, the tool is placed on the tool rest and moved around manually to produce the desired machining operation.

The hand-held tool eliminates the need for various tool-holding parts like toolpost, feed screw, cross rail, etc., thereby reducing the size of the machine.

Speed lathes are also known as wood lathes and are commonly used in woodworking applications such as turning, sanding, polishing, and centering.

Using a wood lathe is comparatively more simple than other metal lathes that involve handwheel controls to position the cutting tool.

Therefore, a good wood lathe requires a high-speed and low-torque configuration to produce a smooth machined surface on wood.

Bench lathe

Bench lathes are small-sized lathes that can fit on a regular workshop bench.

These lathes offer high accuracy and are generally used in applications like grinding, watchmaking, etc., where machining of small objects is required.

CNC bench lathes, such as Proxxon PD 400, can be used for high accuracy machining of soft materials.

Semi-automatic Lathe

In this type of lathe, the operator mounts the workpiece on the chuck and sets the automatic speeds and feeds for the process.

However, automation can only be applied to simple operations like turning, threading, taper turning, etc., where complex geometry is not involved.

Therefore, semi-automatic lathe machines are ideal for mass production where simple cuts are required with a high surface finish.

Special Lathes

Apart from the traditional lathes, there are some special lathes that are used for performing complex machining operations that a traditional lathe cannot handle.

These lathes include multi-spindle lathes, multi-axis lathes, swiss lathes, vertical lathes, T-type lathes, etc.

CNC Lathes 

Computer numerical control (CNC) lathes are fully automatic lathes that can handle complex geometries with minimal human involvement.

These machines work similarly to other CNC machines and require special CNC software for operation.

They take in the design from CAD software, use CAM software to convert the design into G-codes, and then the computer system controls the movement of the tool to produce the desired cut.

CNC lathes, such as Tormach 8L, are ideal for mass production where high accuracy and quick cycle time are of value.

Depending upon their power, torque, and speed, these machines are available under different categories, such as CNC lathes for metal working, woodworking, etc.

Lathe Operations in Machining

Lathe is a versatile machine tool that can be used for performing various machining operations, such as turning, facing, grooving, threading, boring, rotary broaching, etc.

Turning

Turning is a machining process in which the tool moves along the length of the rotating workpiece to produce the desired product. This operation is used for producing cylindrical objects by reducing the outer diameter of the material until the required size is achieved.

Turning operations are generally performed in two manners: rough turning and finish turning.

During rough turning, the primary aim of the process is to remove the material and attain the required size.

Whereas in finish turning, there is comparatively less material removal and the primary aim is to achieve a high surface finish.

Turning operations can also be performed to produce different shapes on a cylindrical workpiece, such as step turning, taper turning, chamfer turning, contour turning, and form turning.

The tool used for performing this operation is known as a turning tool.

A rough turning tool has a tool geometry ideal for removing the maximum amount of material, whereas a finishing turning tool is designed to remove less material with a high surface finish.

Facing

Facing is the machining process in which the cutting tool removes material from the leading face of the workpiece. This operation is generally performed to reduce the length of the workpiece and produce a smooth face, perpendicular to the rotating axis of the workpiece.

A facing tool is used for this operation.

During this process, the tool is moved radially inwards to the workpiece thickness, thereby removing material and reducing the workpiece length.

The tool is mounted on the tool post that moves perpendicular to the rotating axis and removes the material from the face of the workpiece.

Grooving

Grooving is similar to facing but is performed at variable lengths of the workpiece to remove the material up to a certain depth, thereby producing a groove. The tool is moved radially into the workpiece to produce the groove, and the width of the groove is dependent upon the tool size.

However, if the edge of the cutting tool is plunged into the workpiece until it reaches the center, the part of the workpiece separates from the stock and drops off on the lathe bed.

This process is known as parting and is used for cutting cylindrical workpieces at desired lengths.

Grooving can also be performed on the face of the workpiece by placing the cutting tool along the longitudinal axis of the lathe.

The longitudinal movement of the cutting tool determines the depth of the groove, and the process is generally known as face grooving.

A grooving tool is used for this operation.

It consists of a cutting head that removes the material in a particular pattern, depending upon the shape of the tool head.

Knurling

Knurling is the process of creating serrated patterns on a cylindrical workpiece to increase friction and provide a better grip. Apart from providing grip, it also enhances the aesthetic value of a workpiece. A knurling tool consists of one or more wheels with the desired pattern embossed on their surface.

These wheels are pressed against the rotating workpiece and the pattern is rolled into the surface of the material.

Threading

Threading is the process of removing material to produce a spiral pattern on the outer surface of the workpiece. Each element of the spiral pattern is known as a thread, and a threading pattern is generally defined by the thread angle and the distance between adjacent threads (pitch).

Threads can also be cut on the internal surface of the workpiece, such as nuts used in a nut-bolt assembly where the nut has internal threads and the bolt has outer threads.

The process of cutting internal threads on a workpiece is known as tapping, and is generally performed by inserting the tool in an already drilled hole and removing material from the inside.

A thread cutting tool is mounted on the tool post and moved along the length of the workpiece to produce the desired threads.

Whereas, when cutting internal threads/ tapping, the tool is generally mounted on the tail stock and moved axially inwards and outwards of the already drilled hole.

Drilling

A typical drilling operation consists of a high-speed rotating tool that plunges into the workpiece to produce a hole of desired diameter. However, in lathe drilling, the workpiece rotates at high RPM and a non-rotating cutting tool plunges axially into the surface of the workpiece to produce the desired hole.

A drilling tool is a multi-point cutting tool that is mounted either on the tail stock or on the tool holder of the lathe machine.

Boring

Boring is similar to drilling, but instead of removing the material to make a hole, boring expands the internal diameter of an already drilled hole. This process can also be used to perform internal turning operations like step turning, taper turning, etc.

A boring tool is a bar-shaped cutting tool with a cutting head that removes material to enlarge a hole.

Modes of Work Holding on a Lathe

The operations performed on a lathe consist of a rotating workpiece and a moving cutting tool that removes the material from the workpiece.

However, lathe operations can be of three different types, depending on the workpiece holding.

Face Work

When the workpiece is clamped on one end and free on the other end, like a cantilever beam, it is known as face work.

In face work, the workpiece is mounted on the spindle at the headstock end and the cutting tool has access to the curved surface and a face of the workpiece.

Generally, this type of work holding is used when performing facing operations.

Face work configuration is not recommended for applications where strong radial cutting force is to be applied on the workpiece.

This is because, applying strong force at the leading end of the workpiece can result in breaking or dismounting of the workpiece from the chuck, thereby damaging the workpiece.

Between Centers

Between centers configuration is generally used when working on long workpieces.

In this technique, the workpiece is clamped at both ends by headstock and tailstock to provide greater support for the entire length of the workpiece.

This configuration is ideal for working on long workpieces, or for applications where strong cutting force is to be delivered radially.

Eccentric Turning

Eccentric turning is when, during the process, the workpiece is re-mounted on the spindle with a new axis of rotation, parallel to the previous axis.

The new axis of rotation is set by manipulating the jaws' arrangement of the chuck that holds the workpiece.

This process produces a non-symmetric product with various cross-sections that are individually symmetric.

Generally, this type of work holding is used for producing camshafts.

Applications of a Lathe

The versatile nature of lathes makes them ideal for various applications that involve machining of material to produce axisymmetric workpieces.

Heavy-duty lathes such as engine lathes, turret lathes, automatic lathes, etc. are ideal for metal machining applications and are generally used for making various automobile parts such as camshafts.

A bench lathe is used for machining small size applications such as watches, jewelry, medical equipment, etc.

Similarly, high RPM speed lathes are ideal for applications that involve machining of wood.

These machines can create woodworking items that are symmetric around an axis, such as cylindrical legs for furniture, bowls, etc.

Apart from these, a lathe machine can also be used to perfectly align two cylindrical parts for joining operation (welding).

Special CNC lathes with a higher axis system can also be used for producing complex engravings on the surface of the workpiece.

Things to Consider Before Buying a Lathe

There are various things that you should consider when buying a lathe that suits your requirement.

Size

The size of a lathe is generally denoted in A x B format, where A is known as "swing" and denotes the vertical distance between the center of the headstock and lathe bed.

It determines the maximum radius of a workpiece that can fit on that lathe for machining.

Whereas B is known as "bed size" and denotes the horizontal distance between the headstock and tailstock.

The bed size determines the maximum length of a workpiece that can fit on the lathe for machining operations.

For example, a lathe machine with a size of 10 x 20 can fit a workpiece with a maximum radius of 10" and a maximum length of 20".

Furthermore, it is also important to consider the footprint of the lathe machine to ensure that it fits the available space in your workshop.

Speed, Torque, and Power Configuration

The speed, torque, and power configuration depend upon the material, size, and weight of your workpiece.

Generally, when working with wooden workpieces that are small and light in weight, it is recommended to have a high-speed lathe with relatively lower power and torque.

Similarly, when working with large and heavy objects (like metals) is your primary requirement, it is ideal to have a lathe machine with high torque and power to rotate the heavy workpiece.

Therefore, on the basis of their speed and power, lathes can be classified as wood lathes and metal lathes.

Although it is difficult to have a perfect configuration suitable for all requirements, most lathe machines provide a speed control level that changes the speed, power, and torque configuration to best suit your application.

This ability to control the speed and power makes it possible to use a wood lathe for machining soft metals and vice-versa, but at the cost of quality and accuracy.

Material Capability

Material capability of a lathe is an important factor that should be considered when buying a lathe.

It is generally dependent upon the power, speed, and torque configuration of a lathe.

A lathe with high torque can produce better machining results on metal workpieces compared to a lathe with a faster spindle speed which is ideal for woodworking.

Furthermore, the machining capability of a lathe is also dependent upon the degree of freedom (number of axes) of the lathe.

A lathe with a higher axis system can machine complex geometries with higher precision and quick cycle time.

Belt Drive or Direct-Drive Spindle

The transmission used for driving the spindle plays an important role in determining the performance of a lathe.

Belt drive is one of the most commonly used transmission systems in lathe machines.

However, when compared to a direct drive, a belt drive provides slower speed variations and lower power output.

A typical belt drive will take almost twice the time taken by a direct-drive spindle to reach a speed of 0-3000 RPM.

Tools Required for your Application

Apart from considering the cost incurred in buying the lathe, the tools required for your application can also affect the budget of your lathe machine.

Generally, carbide turning tools are recommended for high material removal, smooth surface finish, and long life.

CNC Lathe vs Traditional Lathe

When buying a lathe machine, it is important to consider the type of lathe suitable for your application.

There are various different lathes that are used for different machining scenarios.

After selecting the suitable type of lathe machine, it is also important to consider the choice of a CNC lathe.

A CNC lathe is generally more expensive than a traditional lathe but can provide higher accuracy and repeatability.

Therefore, for applications that require machining of complex geometries with high accuracy, it is recommended to go for a CNC lathe.

Furthermore, CNC lathes are a good investment for future applications where mass production of products with quick cycle time can be desirable.

Frequently Asked Questions (FAQ)

What are the three main types of lathe?

The three main types of lathe machines are center lathe, benchtop or mini lathe, and CNC lathe. Center lathes can further be classified into engine lathes and speed lathes. Whereas CNC lathes include all types of metal lathes with a computer system to automate the machining process.

Can we use a bench lathe for machining metals?

Yes, a bench lathe can be used for machining metals. However, these machines are comparatively less rigid than center lathes and are therefore ideal for machining soft metals like brass, aluminum, copper, zinc, and other non-metal materials.

What is the difference between a Capstan lathe and a Turret lathe?

Capstan lathe is a lightweight lathe ideal for machining soft materials, whereas a turret lathe is ideal for heavy-duty machining. In a turret lathe, the tool post can be moved along the lateral axis, which otherwise can't be moved laterally in a Capstan lathe. Moreover, Turret lathe is ideal for working on larger workpieces compared to a Capstan lathe.