Okay so I’ve readjusted the belts’ tension this morning. The X belt was a bit loose and the Y belt was a bit too tight, strangely enough. Both in the green though. So I set them to the middle of the range. Good thing I checked anyway because all the screws on the X motor mount were so loose they were on the verge of letting go completely.

And since I was at it, I cleaned the entire enclosure and re-lubed the rails and the linear bearings.

However, I don’t think the printer faulted because of any of this: I checked where the hard limit was in X and Y and found that the nozzle came right at the edge of the previous prints that failed on the left and on the top:

Image

Image

At this point, I’m convinced the printer got lucky twice when it printed that print right, and when it didn’t, it was the result of the carriage hitting the limits when the motor(s) overshot the extreme positions a bit. I re-sliced that print to leave some margin with what PrusaSlicer believes are the limits of the printing area and I came to a perfectly printed set of parts today. And the new set I started 2 hours ago seems fine too.

So I think the lesson here is that PrusaSlicer is a bit too optimistic with how large you can print, both in X and Y. It pays not to believe it too much.