<p>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.</p>

<p>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.</p>

<p>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).</p>

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

[{'answer_id': 3066, 'author': 'darth pixel', 'author_id': 1211, 'author_profile': 'https://3dprinting.stackexchange.com/users/1211', 'pm_score': 3, 'selected': False, 'text': '<p>I assume you did everything according to the instructions but here is a checklist of what could be possibly wrong:</p>\n\n<ol>\n<li>Friction - check if you can rotate/move parts without lot of resistance</li>\n<li>Screws - check if screws on couplings are tight and they don\'t slide over a shaft or thread</li>\n<li>Stepsticks - check if they are cooled properly and similar (as there are two of them)</li>\n<li>Carriage nuts on threads - check if they do not slide out of their nests while [the x-axis] carriage goes up</li>\n<li>Filament - check if filament unrolls without resistance which can eventually cause [the x-axis] carriage to hang.</li>\n</ol>\n\n<p>IMO #2 and #3 are the most possible cause</p>\n\n<p><a href="https://i.stack.imgur.com/4Hd33.png" rel="noreferrer"><img src="https://i.stack.imgur.com/4Hd33.png" alt="Diagram of issues 1, 2 and 5"></a></p>\n'}, {'answer_id': 3067, 'author': 'Sean Houlihane', 'author_id': 4927, 'author_profile': 'https://3dprinting.stackexchange.com/users/4927', 'pm_score': 3, 'selected': True, 'text': '<p>So after reading the instructions more carefully, ANET do cover this in their operating instructions under <strong>troubleshooting</strong>. 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 <code>SHCS</code> 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.</p>\n\n<p><a href="https://i.stack.imgur.com/5k8Wh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5k8Wh.png" alt="From ANET manual"></a></p>\n'}, {'answer_id': 8021, 'author': 'Cactusbone', 'author_id': 14275, 'author_profile': 'https://3dprinting.stackexchange.com/users/14275', 'pm_score': 0, 'selected': False, 'text': '<p>From <a href="http://3daddict.com/anet-3d-printer-common-mistakes-fix/" rel="nofollow noreferrer">http://3daddict.com/anet-3d-printer-common-mistakes-fix/</a></p>\n\n<p>The motor shaft and the threading rod must have space between them in the flexible coupler.</p>\n\n<p>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.\nThis will allow the coupler to flex, and thus should handle small misalignments of the brass nut.</p>\n\n<p>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</p>\n'}]
['https://3dprinting.stackexchange.com/questions/3065', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/4927/']