Z-axis steppers and bed alignment problems

Question

I've actually solved this, but I think its still a useful question which I don't think is easy to answer with existing questions.

As soon as I'd built my ANET-A8 (Prusa i3 DIY kit), I found I was having problems with the extruder crashing into the bed. Although I thought I'd adjusted the bed leveling OK, the calibration seemed to keep getting messed up.

I tracked this down to two factors. First, I was winding the extruder head up some distance before loading the filament and starting a print. Second, at roughly half-way up the axis, the right-hand thread seemed to be getting stuck (more often when moving up than down).

What wasn't clear (and not mentioned in the building instructions) was what might cause this problem.

@SeanHoulihane There's no such thing as a "clone". The Prusa design is open-source and in my opinion, "Prusa" refers to any number of designs. — Tom van der Zanden, Nov 21 '16 at 12:54
@TomvanderZanden Thanks for clarifying - I edited the tag :) — Sean Houlihane, Nov 21 '16 at 13:10
In many open source projects the name is trademark, while the designs are copyleft, the company still wants to maintain their brand (and reputation). However, I don't know Prusa's feelings on it. — HaMMeReD, May 11 '17 at 19:16

score 6 · Answer 1 · edited Nov 21 '16 at 17:50

6

I assume you did everything according to the instructions but here is a checklist of what could be possibly wrong:

Friction - check if you can rotate/move parts without lot of resistance
Screws - check if screws on couplings are tight and they don't slide over a shaft or thread
Stepsticks - check if they are cooled properly and similar (as there are two of them)
Carriage nuts on threads - check if they do not slide out of their nests while [the x-axis] carriage goes up
Filament - check if filament unrolls without resistance which can eventually cause [the x-axis] carriage to hang.

IMO #2 and #3 are the most possible cause

edited Nov 21 '16 at 17:50

Greenonline

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answered Nov 21 '16 at 10:58

darth pixel

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`caret nut` is a new term for me. – Sean Houlihane Nov 21 '16 at 11:01
well - here is top left elem (prusa i2) where such nut sits http://3dprinter.my/cart/images/Reprap%20Prusa%20i2%20Printed%20Parts%20Black.jpg more or less the same is in prusa i3 – darth pixel Nov 21 '16 at 11:11
I don't think `caret nut` is a real word. It is probably a mistranslation. – Tom van der Zanden Nov 21 '16 at 12:53
With (2), I had the spindle and the thread pressed tight together, the coupling was unable to bend... – Sean Houlihane Nov 21 '16 at 15:46
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@TomvanderZanden - I think `caret` should actually be `carriage` – Greenonline Nov 21 '16 at 16:58
@SeanHoulihane the issue is to have screws properly screwed – darth pixel Nov 21 '16 at 17:10
@darthpixel - Would you happen to have a source for the image and the checklist? Just to check the intended meaning of `caret`. I have downloaded the Anet [troubleshooting guide](http://www.anet3d.com/English/Technical_Support/Customer_Service/109.html) but it was not mentioned in that document. – Greenonline Nov 21 '16 at 20:21
@greenonline checklist and image source, both come from my head :) let's forget this caret thing, I've just changed it in my ans – darth pixel Nov 22 '16 at 00:21

Sean Houlihane · Accepted Answer · 2016-11-21T15:44:53.670

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So after reading the instructions more carefully, ANET do cover this in their operating instructions under troubleshooting. On closer inspection, I realised that the brass nut following the right hand thread seemed to be out of alignment with the stepper at the bottom. Fiddling with the flexible coupling helped a bit, but what I needed to do was place the assembly at the tight point, slacken the 3 bolts marked SHCS in the diagram, then tighten them again. I was expecting I might need to open out the holes, or re-make the white (factory printed) part, but this wasn't necessary.

edited Nov 21 '16 at 15:44

answered Nov 21 '16 at 11:13

Sean Houlihane

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ha! so there is caret nut :) it's good to hear you've solved it (btw: my suspicion about 1. assembling according to instruction was priviledged) ;) and 2. that there is a problem was priviledged too) – darth pixel Nov 21 '16 at 11:42
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I don't think `caret nut` is a real word. It is probably a mistranslation. – Tom van der Zanden Nov 21 '16 at 12:53
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@darthpixel - I would wager that `caret` actually means `carriage`, as in _the x-axis carriage_. Mostly because of the phrase in Tom's answer, _which can eventually hang caret_, which probably should be _which can eventually hang [the x-axis] carriage_ – Greenonline Nov 21 '16 at 16:57
where did you find this under troubleshooting, I think Im having the same issue. Can't find what you are refereing to. – user6668 Apr 04 '17 at 21:38
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Found it in the A8 Operation instruction-1.1.pdf file provided on the SD card, page 66 – Cactusbone Jan 20 '19 at 12:50

score 0 · Answer 3 · answered Jan 20 '19 at 12:47

From http://3daddict.com/anet-3d-printer-common-mistakes-fix/

The motor shaft and the threading rod must have space between them in the flexible coupler.

That means unlocking the coupler from the motor shaft and moving it up a bit, in the end the threaded rod nearly touches the printer top hole instead of having like a 1cm gap. This will allow the coupler to flex, and thus should handle small misalignments of the brass nut.

That's about point 2 of @darth-pixel answer, but before locking the screws, make sure to have empty space between rod and motor shaft

Z-axis steppers and bed alignment problems

3 Answers3

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