Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 401)

Spindles
Chapter 17
17-3
The S-word units represent revolutions per minute (RPM) in most cases.
Only during CSS programming are the S-word units different. While CSS
mode is active, the S-word units represent surface feet per minute. Only
the controlling spindle can change its S-word mode from RPM to CSS.
The G96 command maintains a constant cutting speed (programmed by the
S parameter) by monitoring the cutting tool’s position with respect to the
center line of the spindle.
In the G96 mode the S-word is used to program the cutting speed. Actual
units for the S-word are surface meters per minute in metric or surface feet
per minute in the inch system. To maintain a cutting speed of 200 m/min,
for example, write the program as:
G96 S200;
G96 mode must also first be enabled by programming an M58 code. See
the notes on CSS on page 17-6 for details. The G96 code is modal and
remains active until it is cancelled by the G97 code or disabled with an
M59 code.
Important: When changing from G97 to G96 mode, if an S-word is
specified in the G96 block, the cutting speed changes to the value indicated
by the S-word. If no S-word is contained in the G96 block the control uses
the current cutting speed of the tool as the CSS cutting speed. The spindle
speed then changes relative to the tool position to maintain this CSS
cutting speed.
Important: The system installer determines in AMP what axis is used to
determine the cutting diameter. The programmer has the option of
changing the diameter axis by programming a P-word when in the G96
mode. P-words range from P1 to P9. A P-word to change diameter axis
may be programmed in any block where in the G96 mode as long as that
block does not contain a dwell. Refer to the system installer’s
documentation for details on what P-word programs the axis that is
perpendicular to the part diameter. Normally the P-word is not
programmed for CSS. If not programmed the system installer’s default
axis is used. This manual assumes the X axis determines the cutting
diameter.
Your system installer determines CSS axis assignment in AMP. You can
change the CSS axis by programming a P-word (P0 through P9) in the
G96 block when activating CSS.
17.1.1
Constant Surface Speed
Mode (G96)