I have a Crafsman 8" variable speed grinder that I purchased on the cheap (60.00), when I first started using it, I set the dial to 1800 and started the grinder. It started up great and keep the speed for a couple seconds and then jumped up to full bore. I tried turning the dial on the grinder, but now it just runs at full speed no matter what I do. My question is, does anyone know what might have happened and/or how to fix it? I am thinking about getting a dimmer switch to plug the grinder into just so I can get it back to the lower speed. This is the grinder... https://www.sears.com/craftsman-professional-variable-speed-8inch-bench-grinder-21162/p-00921162000P