RPM sensor / digital tachometer probe

This probe can be used as the counterpart to your digital optical tachometer. They measure RPMs by changes of light/dark, normally reflective stickers are supplied to attach them to your spinning thing you want to measure.

This design can be used for drill chucks, 3-jaw chucks or similar.

Print the two parts oriented as they come from the STL file in different colors, the smaller one (¼ circle) with high reflection (white oder any light color) and the other one (¾ circle) with low reflection (black or any dark color) and simply glue them together.

PLA with 20% infill will do the job.

Diameters are 10mm/30mm, the shaft is 45mm long, overall length is 55mm. But you can resize them as needed in your slicer.

To measure your RPMs just point your tachometer to the large lower surface or to its circumference, both will work.