It's located in my dad's workshop which is in the basement. Originally none of the outlets in his shop were on a GFCI but I changed that. :thumbsup:
Peter,
When does the 10% speed occur ?
As you increase from 0% speed to 10% speed ?
or
As you decrease from 100% speed to 10% speed ?
It was my passing thought that the EMI, being of much higher frequency than the 60cycle,
might leak through and out of the mill at a higher rate than the 60cycle.
That being because Electrostatic Coupling (capacitive coupling) is greater for higher frequency signals.
Is there any grease on the mill ? Could be conductive, or contain metal shavings.
Are there any metal shavings on the mill ?
Metal shavings could be conductive, and could contribute to capacitive leakage at EMI frequency.
Have you tried changing the cord-plug ? Check for strands of wire fraying.
My VOM has both milli-Volt and micro-Amp ranges. Have you tried such a VOM ?
Have you tried monitoring the voltage at the mill using an oscilloscope. ?
When your mind and all else is failing, Shoot in the Dark !
Try something different.