This might be of interest if the VFD's on a lathe - I've hooked up a slider pot on the cross-slide, so the spindle speed increases as you get to smaller diameters. I've found it make a big difference to the finish when facing/parting-off.
The parts are all pretty standard stuff, the slider's sprung to the minimum position and a stop on the cross-slide hits a lever which in turn moves the slider off minimum as you approach the spindle axis - result is "almost-constant surface speed", a bit like the big boys have on their CNC machines
The max and min pots set the range the slider changes the speed through, by setting the voltage at the max and min ends, maximum to just above half-speed on the "max" pot, Zero to a bit below half-speed on the "min" pot.
This assumes your VFD wants a 10K pot, if a different value, just scale all the resistance values!
Just my ha'pennorth,
Dave H. (the other one)
