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Mach3 has a bug in the initial commanded spindle speed under PWM control. It manifests itself as resulting
in a higher initial speed than that requested.
For example, on my lathe, if you request S500 the spindle will go to 643rpm. If you then perform either of the
following actions, the speed will come back to the requested 500rpm:
1. Press Spindle Speed Override Reset Button, or
2. Issue another S500 command from Mach3 via DRO or MDI
Subsequent requested spindle speeds are then true until you stop the spindle and start again.
I don’t know if this bug exists under Step and Direction Controlled spindles because all my machines use
PWM and they all exhibit this problem. It has nothing to do with Smoothstepper because one machine is not
controlled with a Smoothstepper and it behaves exactly the same.
My workaround for this bug is to ensure that the following G Code example (or equivalent) to start the spindle
is inserted into all of my cnc programs:
M3 S500 (Request Start Spindle CW at 500rpm but it goes to 643rpm)
G4 P1 (Wait for 1 second)
S500 (The spindle then comes back to 500rpm)
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