I have a variac stashed somewhere. I have saved it for many years, just to do some foam cutting.
Well, When I need it, I couldn't find it, but I did find an old AstroFlight power pack battery charger.

I set it up with my home made bow (.014) fishing wire. and it works great. the power on this charger is adjustable, so with a little playing around I was able to get a very nice smooth cut.