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« on: July 30, 2022, 09:23:43 AM »
Your speed readings for each speed except the two highest are all close to 22% high.
The PMDX-107 used with most VFD's can normally achieve a speed setting accuracy of 5% or better over most of the range.
First, make sure that you have the default slot for pulley 0 configured in Mach4 to Min RPM of 0 and Maximum of 24000 (or 24001 if Mach complains when you select 24000). These numbers are used by Mach4 to calculate the PWM percentage. The case of protecting the spindle from cooling problems is normally covered by the motion controller plug-in overriding the minimum PWM. The PMDX motion controllers allow this, but I am not sure how this would work for a SmoothStepper based system.
I suspect that your VFD or its internal settings are scaling the input voltage by +22% and the two highest speeds are being limited by the maximum 400 Hz range of the VFD.
You could try using Mach to request some speed safely below the limit, say 18000 and then use the CAL pot on the PMDX-107 to get 18000 at the spindle. Not sure how this will affect the maximum speed you can reach, but it should cure the +22% over most of the range.
Alternatively you can dive into the gain or span settings in your VFD's parameters, but this can get complicated and confusing quickly. If you go this route be sure to document your VFD's parameters before changing them. It might also be informative to see if any of these parameters are not currently set to their factory defaults. Lastly if things are really messed up you can use the VFD's reset to factory defaults option.