Lathe Axis Explained with Graphics

From traditional 2-axis lathes to expensive 6-axis CNC lathes, the number of axes in a lathe vary quite a bit.

The flexibility of a lathe to perform operations depends upon the number of axes of the machine.

Modern CNC lathes have multi-axis systems that make it possible to machine complex geometries with quick cycle time.

This article presents a detailed graphical guide about the axis system of lathe machines.

Axis System in a Traditional Lathe

A manual Lathe's axis system generally consists of 2 axes, where the tool moves front-back along X-axis (laterally) and left-right along Z-axis (axial). However, modern CNC lathes can have up to 6 axes, where X, Y, and Z are the linear axes, and A, B, and C are the corresponding rotational axes.

A typical lathe consists of a chuck and spindle assembly that holds the workpiece and rotates it at high RPM.

The tool is fixed on the tool post that moves along the X and Z axis to perform the desired machining operation.

A two-axis lathe can perform operations such as facing, turning, tapering, knurling, threading, boring, drilling, etc.

Although two-axis lathe machines can perform almost all the turning operations, lathes with higher axis systems can perform similar tasks with greater accuracy and in less time.

Different Axes Used in CNC Lathes

Axis	Function
X-axis	Depth of cut (front/back of the workpiece)
Z-axis	Axial movement of the cutting tool (left/right)
Y-axis	Perpendicular to X and Z (Up/Down movement)
A-axis	Rotation around X-axis (Roll)
B-axis	Rotation around Y-axis (Pitch)
C-axis	Rotation around Z-axis (Yaw)
U-axis	Parallel to X-axis (increment/decrement in X-direction)
V-axis	Parallel to Y-axis (increment/decrement in Y-direction)
Z-axis	Parallel to Z-axis (increment/decrement in Z-direction)

Computer Numerical Control (CNC) lathes are an advanced version of traditional lathe machines in which a computer system controls the various feeds and speeds of the machining operation.

Operating these CNC machines requires good design skills to prepare the design, and a CNC software that will convert the design into corresponding G-codes.

These G-codes convey the information to the controller system and impart movement along the desired axis.

There are a total of 9 axes involved in advanced CNC systems, which include three linear axes, three rotational axes, and three incremental axes.

Linear Axes

Linear axes consist of the basic X, Y, and Z-axis that guide the movement of the cutting tool along the vertical, horizontal, and depth of the workpiece, respectively.

The X, Y, and Z-axis provide a CNC machine with 3 degrees of freedom, which means that the tool can move around freely in the XYZ plane.

Basic CNC lathe uses a 2-axis system (X and Z-axis), similar to the traditional lathe, and can be used for automation of basic lathe operations.

Rotational Axes

Rotational axes provide the ability to rotate the workpiece or the cutting tool along the X, Y, or Z-axis, and these axes are named A, B, and C-axis respectively.

A-axis is the rotary axis corresponding to X-axis, and the movement of the tool along A-axis is known as "roll".

Whereas B-axis is the rotary axis corresponding to Y-axis, and the movement along this axis is known as "pitch".

Similarly, C-axis is concerned with the rotation about Z-axis, and the movement along this axis is known as "yaw".

These axes generally provide a 180° rotation to the tool in their respective planes and add to the degree of freedom available on a CNC machine.

A CNC lathe with the flexibility to rotate the tool around these axes can produce complex geometries with higher precision and faster cycle time.

Incremental Axes

The incremental axes system consists of U, V, and W axes that are used for the ease of CNC programming.

Unlike other axes, the incremental axis does not provide any additional degree of freedom to the machine.

These are secondary axes and are considered parallel to the linear X, Y, and Z-axis system.

The U, V, and W-axis are used to provide increments while positioning the tool along the X, Y, and Z-axis, respectively.

Multi-axis CNC Lathes: Axes Explained

Apart from the traditional 2-axis lathes that use XY and UZ axis systems, there are various modern CNC lathes that can have 3, 4, 5, and even 6-axis systems.

These machines are used for performing complex machining operations with quick cycle time and high precision.

3-Axis CNC Lathe

A 3-axis CNC lathe consists of a cutting tool that can move along the conventional X and Z-axis with an additional movement along the Y-axis.

This adds to the degree of freedom of the machine and allows the CNC system to position the tool in the XYZ plane.

Generally, most of the good CNC lathes for metal working consist of a 2 or 3-axis system.

Applications of 3-Axis Lathe

The addition of Y-axis enables extra movement of the cutting tool, thereby facilitating easy machining of curves and contours.

This type of 3-axis lathe also provides the ability to integrate an automatic tool changer with the CNC machine.

The tool post moves along the XYZ plane and positions itself for automatic tool change operation, which facilitates quicker machining and enhances productivity.

4-Axis CNC Lathe

A 4-axis CNC lathe consists of X, Y, and Z axes along with a rotational C-axis.

This type of lathe can perform versatile operations and supports automatic tool change.

Generally, when using the rotary tool (C-axis), the workpiece is kept stationary and the rotating tool removes the material, thereby transforming a 4-axis CNC lathe into a milling/drilling station.

Applications of 4-Axis Lathe

The rotational C-axis enhances the functionality of the machine and allows it to perform milling and drilling operations on the workpiece.

This type of CNC lathe is also known as multi-tasking lathe or hybrid lathe, as it can perform the operations of a lathe and a mill.

The high-speed rotating tool can be positioned anywhere in the XYZ plane to remove the material from the desired position.

4-axis CNC lathes can cut and mill on the side of the workpiece, and perform engravings on curved surfaces. These lathes can be used for the manufacturing of gears.

Therefore, it enhances productivity by increasing the speed and functionality of a CNC lathe.

5-Axis CNC Lathe

A 5-axis CNC lathe can perform 3 linear movements and any two of the three rotational movements.

Generally, these machines consist of XYZAC or XYZBC axis system and can access the workpiece for machining from 5 different sides.

These machines are extremely precise and can produce almost any complex shape with a quick cycle time.

Applications of 5-Axis Lathe

The ability to control the tool and access the workpiece from 5 different axes enables it to perform almost every milling and turning operation on a single machine.

It is best suited for producing complex and intricate components that would otherwise require frequent re-orientation of workpiece if performed on a 3 or 4-axis lathe.

6-Axis CNC Lathe

6-axis CNC lathes are complex machines that can perform almost any machining operation.

These machines can access the workpiece from 6 sides, which makes it possible to produce any complex shape without the need for stopping the process to re-orient the workpiece.

6-axis lathes are rarely found because a 5-axis CNC lathe can satisfy all the manufacturing needs with high accuracy and cycle speed.

However, these machines can be found in extremely sophisticated manufacturing units that work on medical and space exploration projects.

A 6-axis CNC lathe is an all-in-one machine that can perform the operations of a lathe, mill, drill, etc.

Programming of 6-axis CNC machining process is an extremely complicated task and requires an extremely skilled machinist to design the process.

For a better understanding, the various movements of a 6-axis CNC lathe can be visualized in the video below.

UVW vs XYZ Axis System in Lathe

Programming a CNC lathe involves positioning the tool by using G-codes.

These G-codes define the coordinates in the XYZ plane to position the tool precisely, thereby performing the desired machining action.

The tool can be positioned in the workplace by using positional coordinates or by the incremental coordinate system.

To understand the difference between UVW and XYZ axes systems, we first need to understand the difference between positional and incremental coordinates.

Positional coordinates and Incremental coordinates

Positional coordinates place the cutting tool with respect to the datum point or origin point.

Whereas, incremental coordinates position the cutting tool with respect to its current position.

For example, let's consider the example below, where we use positional coordinates to perform the following task.

Here, G90 activates the positional coordinates system and G21 sets the units to millimeters.

Next line, S450 M04, sets the cutting speed and rotation direction of the tool.

The command "G00 X20.0 Y20.0" indicates rapid movement of the tool to position 'A', where X and Y coordinates are 20.

Next, we indicate the machine to keep the Y-axis coordinates constant and move the cutting tool to position 'B', where X coordinate, with respect to the datum point, equals 40.

Similarly, we move the cutting tool to position 'C', where X-axis coordinate, with respect to the datum point, equals 60.

Then we end the process by stopping the spindle and calling it to the origin point 'O'.

Similarly, we can perform the same task by using incremental coordinates.

In the first line, G91 activates the incremental mode and G21 sets the dimensional units to millimeters.

The next line, S600 M03, sets the cutting speed and direction of rotation.

Then the G-code, G00 X20.0 Y20.0, positions the tool where the X and Y coordinates equal 20 (position 'A').

Unlike positional mode, here we move the tool to position 'B' by giving an increment of 20 units in the X-direction.

Similarly, we move the tool to position 'C' by giving an increment of another 20 units with respect to its current position (B).

It must be noted that absolute and incremental programming are modal in nature.

This means they remain active unless you program the other one to be initiated.

Therefore, in next line, we use G90 command to activate the positional coordinate system and end the process by stopping the spindle and calling it to the origin point.

UVW and XYZ Axis System

The UVW axis system works similar to incremental mode but provides the advantage of using both, positional and incremental coordinate systems in combination.

This simplifies the programming and saves time by eliminating the need to make complex arithmetic calculations to position the tool with respect to the origin point.

Generally, a two-axis CNC lathe uses the XZ and UW coordinates for programming the machining process.

Programming by using UW coordinates is called incremental programming, whereas programming using XZ coordinates is known as absolute programming.

This can be understood by considering the example of a CNC lathe performing a turning operation and making grooves on the surface of a cylindrical workpiece.

For this operation, positioning of the tool can be achieved by using both, incremental (U, W) and positional (X, Z) axis systems.

The coordinate X42 will position the cutting tool at the leading edge corner (A) of the workpiece.

Then we can use the coordinates Z-60, U-2 to perform the turning operation and reach point B.

Followed by U-15. W-10 to perform the turning operation and make the desired groove on the surface of the workpiece.

Similarly, we can use Z-80, U10 to position the tool at C, followed by U-10, W-10 to make the second groove on the workpiece, and then Z-150, U15 to perform turning operation and reach point D.

Therefore, using the combination of XZ and UW axis systems simplifies the process and saves the time of calculating absolute coordinates for every positional increment in the machining process.

Frequently Asked Questions (FAQ)

What is the degree of freedom (DOF)?

Degree of freedom (DOF) defines the maximum number of independent movements that a machine can perform. Generally, the degree of freedom of a machine is equal to the number of axes it can travel.

What is the maximum number of axes that a CNC can have?

A typical CNC machine can have a maximum of 6-axis system. However, certain CNC machines consist of 2 heads with individual 6-axis system on each. Therefore, making it a 12-axis CNC machine.

What is a swiss lathe?

A Swiss lathe is a complex lathe machine that houses a 5 or higher axis system. This machine can perform various different operations in a single go, without the need to stop the operation for tool change.
Such lathes can perform operations such as turning, threading, milling, drilling, boring, knurling, etc., on very small workpieces that are generally used in the watch industry.