CNC Lathe | G96 Code | Constant Surface Speed (CSS) (Quick Guide)

In this article, we describe how to use G96 code for constant surface speed in CNC lathe machines with all details and examples.


G96 Code Introduction

In this case surface speed is set by S. The spindle speed is calculated so that surface speed is maintained as specified in correspondence with tool position. Even when the work piece diameter is changed, the CNC changes the spindle speed so that cutting speed remains constant. This is called constant surface speed function, with G96 code.

Code G96 indicates the constant surface speed in m/min. i.e. S value programmed after G96 is considered as meters / min.

This is quick guide for G96 command. You will be able to write CNC Program after read this post but if you want more information or all details, please have a look:
“CNC Lathe | G96 Code | Constant Surface Speed”

G96 Code Example

N5 G96 S500 ; 500 m/min
N10 G96 S200 ; 200 m/min

The CNC calculates the spindle speed for the current turning diameter in accordance with the programmed cutting speed.

The speed value stored under S, remains unchanged until a new speed value is programmed. i.e. S value programmed is modal.

When CSS is used the work co-ordinate system must be set so that the centre of rotation meet the Z-axis (X=0).

G96 is modal. It cancels with G97.

Things to Know

  • The surface speed for a block containing rapid traverse is calculated on the basis of the end point.
  • When the power supply is turned ON, the maximum spindle speed is not set ; hence the speed is not clamped.
  • G50 S0 indicates speed is clamped at 0 rpm.
  • The “S” value specified in G96 mode is unaffected by G97 and hence is restored when returned to G96 mode.
  • The surface speed specified in G96 is for the program path and not for the position with tool.

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