The mill uses a set of pulleys to set the speed. Normally you would look at a chart showing speeds and what setting to set the pulley to. The problem I ran into was that I did not have the owner's manual to the mill. The mill was made quite a few years ago and this version is no longer produced. I could not find an owner's manual online because of this. A tachometer would be an easy way to see what speed it is running at, but I didn't have one and didn't want to spend money on something I will only use once.

My solution was to tape a couple magnets onto the end of a drill bit. I used two--one on each side so it would be somewhat balanced. I then wrapped electrical tape around it to make sure they would stay on. To make the sensor I wound some wire around an allen wrench. I attached the leads to an oscilloscope and measured the waveform to determine the speed it was rotating at. Then I recorded the speed and what pulley setting it was on.