# Z-axis steppers and bed alignment problems

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.

• Is it correct to use the prusa tag for clones? Nov 21 '16 at 10:47
• (thanx for creating it) Nov 21 '16 at 11:00
• @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. Nov 21 '16 at 12:54
• @TomvanderZanden Thanks for clarifying - I edited the tag :) 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. May 11 '17 at 19:16

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

1. Friction - check if you can rotate/move parts without lot of resistance
2. Screws - check if screws on couplings are tight and they don't slide over a shaft or thread
3. Stepsticks - check if they are cooled properly and similar (as there are two of them)
4. Carriage nuts on threads - check if they do not slide out of their nests while [the x-axis] carriage goes up
5. 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

• caret nut is a new term for me. Nov 21 '16 at 11:01
• well - here is top left elem (prusa i2) where such nut sits 3dprinter.my/cart/images/… more or less the same is in prusa i3 Nov 21 '16 at 11:11
• I don't think caret nut is a real word. It is probably a mistranslation. Nov 21 '16 at 12:53
• With (2), I had the spindle and the thread pressed tight together, the coupling was unable to bend... Nov 21 '16 at 15:46
• @TomvanderZanden - I think caret should actually be carriage Nov 21 '16 at 16:58

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.

• 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) Nov 21 '16 at 11:42
• I don't think caret nut is a real word. It is probably a mistranslation. Nov 21 '16 at 12:53
• @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 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. Apr 4 '17 at 21:38
• Found it in the A8 Operation instruction-1.1.pdf file provided on the SD card, page 66 Jan 20 '19 at 12:50

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