The G96 command is used to enable Constant Surface Speed (CSS) mode on lathe machines.

When CSS mode is active, the controller automatically adjusts the spindle speed so that the surface speed at the cutting point remains constant as the tool moves closer to or further away from the spindle centre.

Syntax & Parameters

The G96 command is followed by D and S values.

The D value defines the maximum spindle RPM that the spindle is allowed to reach while operating in CSS mode as the tool moves closer to the centre.

The S value defines the surface speed. The units used depend on the current machine units. Metric systems use metres per minute, while imperial systems use feet per minute.

Example Program

N10 G21
N20 G0 X50
N30 G96 D12000 S200
N40 M3
N50 G1 X1 F80

In this example, the machine units are set to millimetres, and the tool is positioned at X50.

The G96 command enables CSS mode with a surface speed of 200 metres per minute, and the maximum spindle speed is limited to 12,000 RPM.

As the X axis moves towards the centre at a feed rate of 80 millimetres per minute, the spindle speed continuously increases to maintain a constant surface speed.

The spindle speed starts at approximately 3,185 RPM and increases as the tool approaches the centre. When the tool reaches approximately X5.2, the spindle reaches the specified maximum speed of 12,000 RPM. From this point onwards, the spindle speed remains capped at 12,000 RPM until the X axis reaches the final position of X1.

CAUTION: Please be aware that the CSS spindle speed does not work with G95 Feed Per Revolution. Using G96 & G95 together may cause unexpected results if used incorrectly. For more information please see G95