i3 MK3S X-Axis Drag triggering crash detection  

New Member

I have an i3 MK3S, and I recently had to take the extruder mostly apart to deal with a fairly major clog. I put it back together, and it was working fine until this morning. To be clear, I have had about 30 hours of successful prints since I reassembled the extruder. However, this morning, I started a print, and while the machine was running through the auto-level protocol, it moved to the first point (basically, home), then it moved to the middle location, then when it was meant to go to the furthest right (closest to the PSU), it got about halfway there, detected a crash, and stopped.

I reset it, then attempted to move the extruder using the LCD controls, and it detected a crash again, about three-quarters of the way to the right (PSU) side. At that point, I tried to move it manually and discovered that, while it moves freely to the left, when I move it to the right, it drags considerably, and grows harder to move the further I go to the right, to the point that it's almost impossible to push it all the way to the right side.

I checked a couple posts here, and one suggested the bearings were being pinched, but I loosened all the screws holding the carriage to the bearings, and the problem persists. Plus, if there was too much pressure on a bearing, wouldn't it cause problems moving in both directions? I don't claim to be an expert in... anything applicable... but that seems to track.


Posted : 11/09/2019 6:18 pm
Noble Member

Well you identified the problem. Until the extruder moves both directions, power off, with no significant drag it will not be fixed.

You only have the motor, the bearings, and the idler to worry about. And the belt itself. Make sure nothing is dragging anywhere,

and both pulleys are centered. For test purposes only, you could try removing one bearing at a time from the extruder and see if one is at fault.

While you are in there - lube them.

Posted : 11/09/2019 6:31 pm
New Member

Okay, quick tinker makes me think the belt was misaligned. Or, more appropriately, the X-axis motor was misaligned, which was causing the belt to move and rub against the edge of the motor, which was causing friction, which was causing "crashes". I tinkered a little with the placement of the motor (mostly just adjusted the screws on the carriage), and it seems to be... better. I'm testing it now.

On that note, is there a way I'm unaware of to fix the alignment and make it much more reliable? Because I don't think I fixed the problem as much as I fixed it for now.

Posted : 11/09/2019 8:53 pm

is your X motor pulley on the correct way round, like in these pictures

YES it does appear to be the wrong way round, but this is how it was designed!!!


I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 11/09/2019 9:57 pm
New Member

I seem to have resolved the first problem by adjusting the belt, but now I'm having a new problem. Namely, the same problem in a different direction. Now, when the machine moves left (away from the PSU), the machine "crashes". The X-axis motor is properly assembled, all I can think is that there's some kind of misalignment? I don't know what's going on, but I haven't been able to print for about a week because the system "crashes" during calibration.

Any thoughts? Has anybody experienced this happening?

Posted : 02/10/2019 4:31 pm
Noble Member

Check for ANYTHING that could be stopping the extruder moving all the way to the left. That includes cable tie wraps, the cable bundle etc. All it takes is the smallest thing and it will mess it up. 

Posted : 02/10/2019 5:14 pm
Illustrious Member

Sticky bearings sounds like part of the problem.  Any time motion gets interrupted for no reason, like mid travel, bearing friction is about all it can be -- or a cable harness that snags on something.

When you built the printer, did you pack the bearings with grease or simply install them with no lubrication?

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 02/10/2019 11:10 pm

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