kenton.h
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Z-axis "stuttering" and moving unevenly

Mar 14, 2019 8:32 pm

Was working perfectly well for a number of prints, then I powered it back up to print something and the Z axis was out of calibration. I tried recalibrating and noticed that the Z-axis was sort of "dancing" -- stuttering on the first slow motion, then catching up to relevel the axis (sort of) but still losing ground against the other side. I swapped the stepper connections and the problem is only on the left-side stepper. Also, I can move the left-side stepper lead screw with my fingers and slight force which I can't with the right. Just got this printer last week -- am really disappointed its failed this fast.

vintagepc
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Re: Z-axis "stuttering" and moving unevenly

Mar 14, 2019 8:36 pm

Check the conical dust caps you had to thread all the way down the Z screws. Make sure they are not binding against the motors.

kenton.h
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Re: Z-axis "stuttering" and moving unevenly

Mar 14, 2019 8:47 pm

Sorry, that was the first thing I did. They are backed off about 1 cm right now, just so I can be sure they aren't binding. Second thing was to release and re-tighten the trapezoid nuts on the threaded nuts and to release and re-tighten the top caps (I actually ran them with no tension one round to make sure they weren't binding. Given that I can move the left axis when its energized, I suspect that there is a shot coil in the stepper but I'd be thrilled to find it isn't that.

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tim.m30
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Re: Z-axis "stuttering" and moving unevenly

Mar 15, 2019 12:14 am

Also check the top brackets ... debris or even a misprint in the cup at the top can cause stumbles. Rare, but possible.

Also - a bad bearing on that side can also be the culprit.

vintagepc
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Re: Z-axis "stuttering" and moving unevenly

Mar 15, 2019 12:35 am

If you've checked all these things, your best bet is then probably live chat in the prusa store. If it is a bad motor (or other part) they'll get you sorted.

kenton.h
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Re: Z-axis "stuttering" and moving unevenly

Mar 20, 2019 4:25 pm

Answer was: blown coil in the left Z stepper. red-blue infinity, black-green 8.2 ohms. Prusa sending a replacement.

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tim.m30
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Re: Z-axis "stuttering" and moving unevenly

Mar 20, 2019 9:48 pm

Let us know how this works out. A motor with a bad coil won't (in theory can't) rotate / step from one position to the next. So it'd never actually move the axis up or down. A broken wire or connector that is intermittent is much more likely.

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