Irregular Spindle Speed

[JAZZCNC]

Ok well the chinese spindle is wired Star(380v) so you need to change it to delta. This will cure your speed problem.
Remove the screws and those gold jumpers can be changed around. Set them like the pic.

Regards the Speed changing when code runs then are you 100% sure the code isn't changing the speed.? Other than that then would need to see the XML to make sure spindle is set correctly.

Regards the VFD Speed then unfortunatly it's one or the other. Yes can make speed adjustable from VFD with quick parameter change but you will lose external control via Mach3.