G96 – Turn on Constant Surface Speed (CSS)

This command is used to enable Constant Surface Speed (CSS) mode in lathe version.

Syntax & Parameters

  • G96 followed by D & S values.
  • D Value - This is to set the maximum spindle RPM that the spindle can achieve in CSS mode as the tool gets closer to the center.
  • S Value - To set surface speed value. The units will be the current machine units in use. Metric uses meters per minute. Imperial uses feet per minute.

Example program

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

  • In the above example CSS mode is enabled with a surface speed of 200 meters per second and the maximum RPM is set to 12000.
  • The X axis starts at X 20 from the center and moves towards the center at a feed rate of 80mm/min. Spindle speed starts at a calculated 3185 rpm and the speed increases the closer it moves to the spindle center. It reaches the specified maximum of 12000 rpm 5.2mm from the center at which time the speed remains at 12000rpm until the X axis reaches the final position of 1mm.

INFORMATION: Units are defined as either inches or mm depending on your machines setup or G20 or G21 command in use.

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

INFORMATION: When CSS turned on in your Gcode program and Auto Spindle ticked in the F1 screen, pressing feed hold will not stop the spindle and it must be stopped and restarted manually.