I found a homemade disk sander at a garage sale. It looked like it would be possible to use it for grinding tools. It was not reversible, so I decided to open it up and find the start winding and disconnect it from the run winding. This turned out to be possible, but the wiring was tight and the connection posts were broken. I pulled out the board that the posts were anchored in, and ended up shearing off a screw. This thing was pretty old. Eventually, I was able to rebuild the board with a modern fiberglass epoxy scrap electronic PCB from a defunct power supply. The motor could now be run in reverse by hand switching the start winding connections. A triple pole double throw toggle switch with disconnected center position worked great for this. Unfortunately, after putting everything together and sticking a zirconium paper sanding disk to the plate, it ran really out of balance It was shaking so much it was probably not possible to grind a tool, but it ground a 1/2" mild steel bar quickly.
To experiment with the balance, I screwed a stainless steel hose clamp around the hub, and captured a large nut. This worked really well. I am now making some better balancers after looking at some of the recent posts. Looks like you need two to adjust the extra degree of freedom for the distance of the mass from the center. I'm surprised that I didn't notice the wobbling when I bought the sander. I guess I was just happy to see it run.
To experiment with the balance, I screwed a stainless steel hose clamp around the hub, and captured a large nut. This worked really well. I am now making some better balancers after looking at some of the recent posts. Looks like you need two to adjust the extra degree of freedom for the distance of the mass from the center. I'm surprised that I didn't notice the wobbling when I bought the sander. I guess I was just happy to see it run.
