text: Y axis crashing on every print after full calibration with wizard – Assembly and first prints troubleshooting – Prusa3D Forum
  Y axis crashing on every print after full calibration with wizard
  This all started when a 4 hour print failed after about 3.5 hours for no apparent reason; printer reported a crash. Resuming the print would not help anything; before the printer would actually start extruding filament it would report a crash again. So I figured I might need to recalibrate the printer.
  I've done the full printer calibration via wizard multiple times now - everything reported perfect condition, perpendicular axes, no errors, no gruesome crashing sounds. First layer calibration correctly starts with homing the extruder at the front left edge of the heatbed, prints the nozzle calibration line thing slightly outside the marked print area at the front left edge of the heatbed, then prints the zigzag and stuff exactly as you would expect.
  However, once the calibration is through, every print I start (all generated gcode from latest PrusaControl) will produce an Y axis crash because the printer moves the bed all the way to the front in the beginning and prints the nozzle calibration line in the *back* left edge of the heatbed. After it is done with that it apparently attempts to move the Y axis even further towards the front, which makes the belts jump and produces horrible sounds. I halt the printer at that point because I don't want it to do more damage that it already has done.
  After I stopped and rebooted the printer at this point, when I check the position of the Y axis in the settings (heatbed still moved all the way to the front) it reports a positive value close to zero and lets me manually crash the axis even further by rotating the knob towards positive Y.
  Is this issue known, and how do I fix it?
  Some calibration stats that might be required...
  Belt status: X 276 Y 247
  Y distance from min: left 10.02mm right 9.99mm
  Measured skew: 0.01°
  0;0 point offset: X -4.04mm Y -0.48mm
  Firmware: latest 3.5.1
  Kit version; delivered and assembled 2 days ago
  Posted : 09/01/2019 4:17 pm
  Re: Y axis crashing on every print after full calibration with wizard
  there are no endstops on the mk3 the firmware senses for resistance to movement and assumes that to be the end of travel,
  if there is something jamming a bit, this may cause a false indication and give the issues you mention...
  to test, lift the Extruder up using the lcd control panel,
  then try sliding the Y axis fully backward and forward, the motion should be smooth with a little resistance from the stepper motor, it should not be jerky
  Posted : 09/01/2019 4:33 pm
  I assume yes, but I'd like to make sure... does stepper motor resistance that increases and lowers like a sine wave while pushing the plate back count as "jerky"?
  And if yes... how do I fix it? Simply increase belt tension on Y axis?
  I'd also sort of wonder why the self test step in the calibration wizard did not report a loose belt?
  Posted : 09/01/2019 4:35 pm
  difficult to answer , is the sine wave period hundreds of times per centimetre movement or one or two times per full Y axis movement?
  Easiest way is to loosen the Y axis toothed gear, and disconnect the y Axis from the stepper motor, then any resistance left, is in the Y axis....
  the resistance could be poor lubrication, failing bearings , poor alignment of bearings, (did you make sure the lines of balls were correctly orientated when you assembled the parts?)
  or it could be problems with the cable management.
  or .... something else.
  Posted : 09/01/2019 5:13 pm
  Neither the one nor the other extreme. Maybe 20-25 times across the whole axis.
  I did make sure the ball bearings were aligned exactly as described in the assembly guide. The first one on a rod in + shape, the second one in X shape. Even took them out of the plastic part a few times because they kept rotating slightly as I pushed them all the way in. I also closely followed the assembly guide on cable management. It doesn't look like there are any cables in the way of the Y axis parts below the heatbed.
  I found some employee blog post on "good" values for belt tension ( https://prusacommunity.com/your-belt-status-and-you/ ) and am currently iterating through tension adjustment and self tests to get closer to the values suggested (255-270). After one self-test, I tried loosening the Y axis toothed gear as you described and checked for resistance - interestingly it was much stronger than with the toothed gear tighened in the beginning, but as I moved the bed back and forth a couple of times it started to become much smoother. And even after re-tightening the toothed gear again, it stayed this smooth.
  Currently running another self-test, then trying to start a print. I'm optimistic!
  Thank you a lot for your fast and detailed answers so far!!
  Posted : 09/01/2019 5:28 pm
  Last self test after adjustment reported belt tension of X=277 and Y=284.
  Started printing the file I got my instant Y axis crash. This time it did drop the nozzle calibration line of filament in the front left corner of the print bed again, as expected. Hope it runs all the way through with no errors. PrusaControl estimated a print time of around 1 hour, which is less than the 3.5 hours before the other print I initially mentioned suddenly failed, but at least it's not ultra short. Will report results.
  Since this thread might be found by others with the same problem later on, I'll add some more detail in one spot which I believe could be important (reassuring you actually have the same problem): Of course I did not start with that 4 hour print right after assembly and very first calibration!
  I have (successfully) printed a good bunch of smaller parts with this printer already before the issues started: two replacement printer parts which I damaged during assembly (45 degree nozzle fan, cracked screw hole / headbed cable shroud, one nut socket wore out), the prusa logo, a self-designed letterbox sign and one of those extruder motor motion visualizers which are featured on the blog and I believe in some official video as well.
  Since I, with my nonexistent experience with 3D printers (the Prusa is my first), can only guess and try to apply logic, it didn't make sense to me that the initial couple of prints were fine and only later started to fail. I felt like if the source of my problems really was that I tightened the belts too much during assembly, then the initial prints would have had to fail as well. (Or, even better, the self-test would have reported it). Guess I was wrong there.
  Posted : 09/01/2019 6:19 pm
  GRIZZ liked
  Print finished successfully!! No crashes!
  Just checking, Julian, did you tighten one grub screw against the flat on the motor shaft?
  Posted : 09/01/2019 11:20 pm
  I tightened both screws in the toothed gear as described in the assembly guide, i.e. one of the two exactly perpendicular to the flat surface on the motor shaft. I might have tightened them a bit too much during the initial assembly. After yesterday's fixing and calibrating, I re-tightened them a little looser (but still without any give).
  Watching my printer via webcam right now, printing since over four hours already without any error 🙂
  Posted : 10/01/2019 12:29 pm
  just a minor addition after I had the same experience, perfect prints for few hours and then Y axis crashing, not solved by any calibration.
  in fact, by checking screws, I found out the hotbed thermistor câble came in the way between Bed support frame and axis, creating a resistance on one size (hence the error "check Y axis length" when attempting calibration.
  i did not heard of such problem before, simply fixed by zip.
  other than that, I am totally happy with MK3 s kit performance, amazed !
  best regards from Paris / Mike
  Posted : 20/05/2020 6:59 am
  since i had the same issue i will tell you how i fixed this. I disassembled the y-achsis so i could pull out the rods from the bearings and re-aligned them perfectly. I also noticed a lack of lubrication and added some, even tho the printer had less than 50 hours.
  Next i figured out the idler at the back side of the printer was too close to the stepmotor so i gave it a little more distance.
  After reassembly i noticed everything went much smoother and see the y-axis crashes were gone.
  So i guess due to thermal expansion during the print ( i use the lack enclosure ), the fits of idler and rods+bearings were too tight and started to create friction and lead to a crash.