Quote Originally Posted by shikano53 View Post
Harbor Freight makes a variable speed controller for a router tool. However that being said; A dimmer switch, potientiometers, router type speed controls only work with universal, brush type motors. A grinder, if memory serves, use an induction motor.
So, yes these will work; but at your or my risk.

The best is a variable frequency drive but by then you might as well just purchase the variable speed grinder/polisher.


correct, while there are workarounds such as a variac- would work for speed- with all of these you are suffering loss of power with loss of RPM. What you would do best with is a tri phase, DC perm mag, even an old treadmill motor and controls. So you get constant power under torque- I confess I didn't read what were building, but I saw a grinder and if you need the power of a grinder motor- you need to pick the right motor first for speed control to not limit your power.