Hey Neale, if you have Mach3 with your VFD can you tell me what parameters you have on the Motor Tuning page for the spindle? I have: Stepsper=1, Velocity=120, Accel=4, Steppulse=2. Dirpulse=2. Some say these settings have no effect on PWM and some say the same but suggesting the Accel/Velocity should be about in the middle of the scale for each