"two variable speed controls in series and it didn't seem to work"
Nope, it won't; those are just very basic SCR controllers, the first one in series would "chop up" the incoming AC voltage, second one would likely NEVER trigger; it'd be cheaper to just not plug the tool in; same result... Steve
BTW, I have one of the ancient (about 50 years old) Craftsman electric die grinders somewhere, haven't used it in decades. too heavy/awkward for much precision - my REAL 5 horse 80 gallon DevAir keeps up with the 3 cheapo air grinders OK. IIRC, the electric was a LOT quieter tho