This is a pointer or indicator for the Thing-O-Matic MK6 Stepstruder to show when the extruder motor is actually turning. I find it very helpful to know if/when the extruder motor is skipping steps and the easiest way is to watch the shaft rotation (or feel the filament feeding with your hand). But the MK6 shaft end is flush with the support bearing, so there was no easy way to mount any kind of flag/indicator. Up until now, I just used a piece of blue tape.

I figuired that I could use a magnet to mount a pointer. The motor shaft is about 6mm diameter, so at first, I tired a single 1/4" magnet to stick to the end....but there are some magnetic fields going through the motor shaft, so the magnet did not like staying centered on the shaft. So next I tried 3 smaller magnets in a circle, and that worked perfectly. I ended up using some 1/8" diameter by 3/8" long rare earth magnets I had left over from some other project that I bought at K&J Magnetics:
http://www.kjmagnetics.com/proddetail.asp?prod=D26. I pressed them into the printed part and it works perfectly.

This is designed for the MK6, but it may work on other models just as well. I am not sure since I do not have others.

I made 2 designs......one is a one piece design, the other is a two piece design that get's glued together with some acetone. They are functionally equivolent, just l look a bit different. I think it is a necessary upgrade to any printer.