Steve,
We have a simple solution.
Instead of trying to calculate the real spindle RPM you can simply inquire on it. Calculating is fine but has so many outside variations to figure in. If you use the example in the TIMER.FIL file as found in the Default CBK file you will find a command called SPINDLERPM which gets the real-time true RPM even if the cutter is being bogged down into heavy material or wearing out.
After getting the RPM you can move the needle gauge, graph bar or update a numeric display with the actually RPM. You may set the timer interval in milliseconds.
TIMER.FIL
SPINDLERPM \1
GAUGE1 \1
Tech Support
CamSoft Corp.
(909) 674-8100
support@camsoftcorp.com www.cnccontrols.com