Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 756)

Chapter 30
Using a 9/Series Dual--Processing System
30-16
Figure 30.5
Multi-Start Thread When Same Start Point Is Used
Process 1
1st Threading Pass
Process 2
2nd Threading Pass
If both processes key off same
marker pulse, then multi-start thread
results.
Marker
12600-I
Use this formula to calculate the amount the start points must be offset:
Shift = q / 360 * F
Where:
Shift -
is the amount the start point of the threads should be offset
q -
the angular distance around the spindle between the two processes
(always measured in the direction of spindle rotation)
F -
the length of the thread lead
For example, assuming your cutting tools are on directly opposite sides of
the spindle,
q
would be 180 degrees. If the thread lead were 20 threads per
inch, F would be 1 / 20. The shift would then equal:
Shift = 180 / 360 * 1/20 = .025 inch.
In cases where the second process is not exactly 180 degrees opposite the
other process, consider the above equation for the direction of spindle
rotation. This consideration is made by always measuring
q
in the
direction of spindle rotation.