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I built a small electronic turntable with the following components: 1- Arduino 2- Sparkfun easy stepper driver 3- Stepper motor 4- Servocity set screw hub. 5- Thrust bearing from mcmaster-carr (square turntable, found here http://www.mcmaster.com/#swivel-plates/=eltxix) 6- Perforated pieces of acrylic attached to both sides of the thrust bearing. I attached the set screw hub to one side and tied down the motor to the other side. The set screw hub is attached to the shaft of the stepper.

The problem I've been seeing is that even with nothing on it, after a quarter of a rotation or so the thrust bearing will start making noise and get stuck. I am not sure but it looks as if the bearings may be getting "squished", probably from some misalignment. The motion overall is not nearly as smooth as when I make the same connection with no thrust bearing. I tried getting a much more powerful stepper motor as well (this one: http://search.digikey.com/us/en/products/PG20L-D20-HHC0/P14334-ND/2417058, 450mNm torque), but the problem is still there.

Do you have any idea what could be going on here, and a good way to fix this?

Thanks!

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The thrust bearing is much larger in diameter than your motor shaft, so any non-parallelism of the faces of what is riding on it to the shaft will be magnified and cause binding. Set screws are generally avoided in precision mechanics because they almost invariably twist the hub at an angle to the shaft. There are better solutions using collet-like tapered mechanisms to grab the shaft. But you still may need to true up the faces on a lathe. And be very careful that your thrust bearing is concentric with the shaft. Bearing mounts can cost more to fabricate than the bearings themselves! – Chris Stratton Oct 23 '11 at 1:14
Thanks Chris - it sounds consistent with what I'm seeing, i.e. the two faces are not spinning exactly parallel to each other and I guess are being pulled together till it stops. Do you have any more information/links on this collet-like mechanism? – aed Oct 23 '11 at 3:44
Finally found it - brand name is "trantorque" they aren't cheap and you may need access to a lathe to bore out the wheel to fit after indicating it true in an adjustable chuck. A cheaper option you can consider is to use a thicker wheel that is just barely a sliding fit, so there's a longer and tighter engagement there's less ability for it to be clamped out of true. – Chris Stratton Oct 23 '11 at 5:31
Thanks again Chris! I'll do some research on that brand. – aed Oct 23 '11 at 6:32

closed as off topic by Leon Heller, Majenko, Kevin Vermeer Oct 22 '11 at 23:06

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