Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 400)

Spindles
Chapter 17
17-2
In this case, cutting speed V is expressed with this equation:
V = (3.14159)(D)(N)/1000
To cut a 150-mm-diameter workpiece at a cutting speed of 200 m/min, the
spindle speed to provide the required cutting speed is calculated to be
approximately 1325 rpm using the above equation. This means that by
designating “S1325;” in a part program, cutting is conducted at a cutting
speed of 200 m/min.
When cutting tapers, which have different workpiece diameters at different
cutting points, spindle speeds need to vary during the cutting process to
maintain proper cutting speed. To compensate for this problem, the control
has a feature to allow designating the required cutting speed V, directly in a
part program. With this feature, the control changes spindle speed as the
diameter of the workpiece changes to maintain a fixed cutting speed. This
feature is referred to as the “constant surface speed mode” or CSS.
The spindle function has two modes:
Constant Surface Speed Mode (G96) maintains a workpiece’s speed
across a tool equal to a desired cutting speed dependent on the working
diameter. See page 17-3.
Constant Spindle RPM Mode (G97) maintains a constant spindle speed
equal to the programmed S-word making cutting speed independent of
the working diameter. See page 17-9.
Spindle Speed (S-word)
Use the S-word to program the spindle speed for all configured spindles.
The common S-word can be applied per spindle by associating the S-word
in the same block with the spindle directional M-codes. See page 17-12
for information about spindle directional M-codes. If no directional
M-code is programmed in the block with the S-word, then the S-word is
applied to the active controlling spindle.
CAUTION: The displayed S-word always shows the
controlling spindle’s programmed spindle speed. When the
non-controlling spindles are configured, their S-word display
must be handled by some other means. See the system
installer’s documentation for display capabilities of the active
spindle speed for auxiliary spindles.