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I have just tried to get uccnc to control the spindle spped of my dc motored lathe.

It has a potentiometer that controls the rpm normally , I removed the output pin the variable 12v signal is on and connected it and the earth pin of the potentiometer to analague 1 and analogue earth on my uc300.

UCCNC send a 0-10v signal to the circuit board inside the lathe and the speed is approx correct with a min duty % of 10 and a max duty % of 80 and it will control the speed up and down via UCCNC

The issue I have is the rpm fluctuates approx 50 rpm ( it does not do this with the original potentiometer) , I have tried the pwm frequency from 10-200 and it makes no real change.

Any ideas ?

what does the PWM frequency do ? optimium setting ?

After watching a few youtube videos I found one franco did with the centroid that had similar issues - his solution was to remove the power supply ground.

I tried that and the issue went away - also the set min/max pwn % also had to change to get the spindle spped calibrated correctly .

Do I run with the main power supply ground removed ? or do I ground the lathe to the power supply ground and reconnect it ?

Do you have a schematics of the spindle controller?

NO , I have verified the machine is earthed to ground but the board earth is not grounded.