How to Measure Drill Press Speed

My new drill press was a big improvement over my old 8″ Delta.  It has many great features and didn’t cost too much.  But I soon noticed a problem.

I noticed something strange about the speed chart under the top belt cover.  It represented a 5 tier pulley setup, but the drill actually has a 4 tier pulley.  That made it impossible for me to determine the actual speed of the drill.  I could still judge the relative speed, but not the actual speed and this really bugged me.

I needed a method to measure the speed of my drill press.  I have an oscilloscope  and I realized with a little rigging… I could use it to measure the speed of my drill.

First I coiled some wire on a nail.

I stuck a strong small magnet on the chuck and clamped the coiled nail near the chuck, so that the magnet would spin past the coils of the nail.

Eureka!  Once I hooked up the coiled wire to the oscilloscope and turn on the drill press… The magnet induced a small current in the wire that appeared on my scope.

Now all I needed to do, was to employ my college degree (BSEE) and calculate the RPM of the drill.

I repeated the measurements for the entire range of the belts on the spindles.  Then I graphed the results.   It’s interesting to see how non-linear the graph is.  I stuck the new chart on my drill and now I have a very exact reference for my drill speeds.


  1. Jon Hague
    February 20th, 2010 at 19:14 | #1

    Pretty smart Alan. I would have just been annoyed that I did not know it.

  2. Alex
    March 22nd, 2014 at 03:34 | #2

    I cruised to your site via a Google link to your shed design beneath your deck. I assumed that you were an engineer based on your ingenuity and attention to detail, the oscilloscope was a dead give away that you’re a fellow EE. Nice work, keep it up.

  3. Jack
    March 15th, 2016 at 16:27 | #3

    Awesome! Not even MacGyver would think about such thing =)

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