I bought what used to be called a router speed controller for less than $20 online. They sell the same one at harbor freight too, but was out of stock. It works really well to slow down my 4 1/2 inch angle grinder. I don't need it running wide open unless I'm trying to grind off a lot, or cutting. Slowing down my sanding discs makes them easier to handle for finishing, plus they last longer, with less heat, and a whole lot quieter. I've been using my Milwaukee variable speed grinder which is much bulkier, and this speed controller works great on my smaller, light angle grinder. Wire wheels last years, instead of days when slowed down a bit. I actually bought the speed controller to slow down the air flow on my Hobbyair 2 fresh-air respirator. It blows way too much air, noisy, and makes the air warm. I can now slow it down, and use it hooked up to my welding helmet with the hose strapped to the chin area blowing fresh air in at a gentle breeze if I want. The speed controller can be used on most "universal" corded motors that use brushes. Not for use on an induction motor like on your drill press.
Last edited by 4100 Fire Truck; Fri Jan 18 2019 01:57 PM.
I didn't know until just now, they have single-phase variable frequency drives(VFD) on the market for induction motors. That would be slick on a drill press, or buffer, etc. https://www.ato.com/single-phase-vfd
I use the same type of speed controller on my 1/4" capacity electric die grinder, which also serves as a light-duty tool post grinder for my lathe. It's sort of like a Dremel tool on steroids and it uses 1/4" shank grinding wheels and carbide burrs. It's a lot more versatile than the air die grinders I've had back when I was doing a lot of porting and polishing of race engine cylinder heads. Some of the speed controllers are more efficient than others. In general, "You get what you pay for!" Jerry
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I made one years ago using a rheostat. Analog dial type light dimmer. I installed it in a receptacle box, male end of a drop cord fed into to it, female end out. I've been using it for years to control the speed of my dremel, 4 1/2 grinder, buffer/polisher.....etc.....