If it is not a mach4 problem then why when I change the pulley settings, does it affect the actual rpm?
I have no answer for that other than what it says in the manual…
"The Spindle dialog allows the configuration and setup of up to 20 spindle rages. The spindle ranges can be gears and or belt settings to allow for a change in the range of speeds available. The reason for the maximum RPM is to allow for proper scaling of the motors RPM on all ranges. The motor RPM is used by motion devices, plugins, VFD's, Lua etc for planning the proper motor RPM to get the requested spindle RPM”.
Whilst the range and the scale can be set, it is my understanding that the problem you are experiencing is one of linearity.
Tweakie.