Layer shift, crash, toolhead falls off  

RE: Layer shift, crash, toolhead falls off

Video of crash

From the side of the printer look along the line of docked print heads; are they all perfectly in line?  Any behind the line represent docks not sufficiently tightened in place - these are likely to be mis-registered at pickup and so at risk of dropping off.

Cheerio,

RE: Layer shift, crash, toolhead falls off

It isn't an issue of the tool misregistering or being picked up incorrectly.

The carriage simply crashes into the end of the x axis, which disengages the tool locking mechanism, so the tool just gets dropped on the bed. 

After chatting with prusa support, it seems the belts were over-tensioned from the factory. After correcting the belt tension, I'm running another long print to see if the problem recurs.

RE: Layer shift, crash, toolhead falls off

At around 0:15 in the video the tool is clearly going waay out of bounds, enough that the sliders contact the side gantry which pushes them leftward to unlock the tool. It shouldn't be going that far off the plate to begin with.

There was one other person that caught thing sort of thing on video but their print was going at a pretty rapid pace compared to this. Guess whatever the real cause of it was never addressed.

It happened three times today, twice while I sat and watched it.

Same gcode file and same spot each time?

I'm also getting some pretty severe audible resonance

It's a known issue. The 6.0.0-alpha firmware addresses it with phase stepping but some, including myself, have had weird issues with the firmware. You're free to give it a shot if the noise bothers you that much. If you don't get issues from it then its a magical update, otherwise you can always change back.

https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.0.0-alpha

RE: Layer shift, crash, toolhead falls off

At around 0:15 in the video the tool is clearly going waay out of bounds

At around 0:03, you can hear the motion stall out. If it is due to over-tensioned belts, I'm guessing it was a case where a large acceleration along a 45 degree angle (driven by only a single motor, unlike X or Y moves) + large friction from the belt tension caused the stepper motor to stall out. The print did complete successfully when I ran at 50% speed for the remainder of the print.

Same gcode file and same spot each time?

Yes and no. In each case, I re-docked the tool and allowed it to re-home and resume printing. The times it repeated were at around the same location, but on different layers of the same gcode.

Thanks for the heads-up about firmware V6.0.0. I was wondering what the latest release added to the stable 5.1.2 I'm running now.

RE: Layer shift, crash, toolhead falls off

Just chiming in, I started experiencing the same exact problem.  Tool hustling along, then crashes headlong into the right rail and drops the head..  Similar to your image, it was while printing a long object at a 45 degree angle on the bed.  I recently printed a very large square, took most of the bed, and had no problem so I don't think it's the object extents per se.

I just redid some calibrations, running a small print now (lubrication tools).  I'm then going to try the same print, but with the parts positioned along the other diagonal.  I'll do a belt tension check before that, thanks @MaSTLab-PI for the suggestion.

ken

RE: Layer shift, crash, toolhead falls off

It has not happened again for me, after about 20 hours of printing large parts (about 75% of the bed filled). However, I haven't yet tried re-printing the part that caused the original failure. If I feel like throwing a quarter roll of filament and a half day away, I may try re-running the same gcode with my re-tensioned belt.

ALSO, my X-gantry alignment was pretty off. I had probably 3 mm of play at the positive-X end of the gantry. I de- and re-tensioned the belts on the negative and positive ends of the X axis, respectively and was able to get a good X alignment with belt tension in the green. I have not tried the homing tower again, but it looked good last time the belt tension app showed me around 75-80 Hz. I will probably give it another go tomorrow to fine-tune.

RE: Layer shift, crash, toolhead falls off

Well my belt tension was a little loose, not much.  But I think I have a clue.

When head 1 is being used and reaching over to the right side of the bed, its harness hangs up briefly on the harness for head 2. I'm thinking that might be knocking something off when it's traveling fast.  I'll need to see if i can catch it in the act, but not sure what to do about it.

ken

RE: Layer shift, crash, toolhead falls off

When head 1 is being used and reaching over to the right side of the bed, its harness hangs up briefly on the harness for head 2.

Ah - good catch. I didn't see any harness entanglement issues, just some motor cogging during fast moves, but it seems like both issues would be exacerbated by large, diagonally-oriented parts.

RE: Layer shift, crash, toolhead falls off

If anyone else suspects belt tensioning issues, this may help you to verify belt tension: https://belt.connect.prusa3d.com/

Open the page on your phone, which will ask for permission to use the microphone on your phone. It will provide step-by-step instructions for each printer to measure belt tension based on the frequency of the belt when pulled and released, much like a guitar tuner.

RE: Layer shift, crash, toolhead falls off

This happened to me today. First time. 

It must be something that sometimes creeps into the gcode from Prusa Slicer. I closed the slicer, resliced the file with different object positions and it worked fine.