Easy/cheap way of halving the mains fequency in order to halve the speed of a single phase electric induction motor?

The problem is to slow the speed of an electric grinder down so that it does not burn woodturning HSS chisels during sharpening. I thought of full wave rectifying the mains and feeding it to a so-called "H-bridge" consisting of four SCR's. The SCR's on the top and bottom opposing sides are triggered together as pairs. Each pair of SCR's are triggered for two consecutive half cycles and so on. Might this work?

Dr.Bill7 years ago
I used a 600 watt dimmer switch to slow my fan to any speed I want.
Wyle_E8 years ago
Grinders don't have synchronous motors, so you don't need to control the frequency. You can try a thyristor speed control. The simplest solution is to grind only for a second at a time, cooling the blade in water between hits. The best is a large, low-speed wet wheel, but those are hard to come by. High-speed steel woodworking tools shouldn't need grinding unless you need to change the shape of the cutting edge. You usually sharpen them by hand, on an oilstone or ultrafine silicon carbide paper.