Randomly shifting Z axis during print MK3
Hi, I have Prusa i3 MK3 kit for about 6 weeks now. Printer counter shows around 21 days (500h) overall print time, so not a little. But strange things are happening in last days. The z axis randomly digg 5mm into print and cause fall of the thing and some kind of fillament ejaculation in space. I'm not sure what is wrong because right now the problem occurs at the calibration stage and digg into the sheet. I proceed the calibration again without any complication, everything works well and print quality is almost perfect, maybe littlebit overextrusion.
1. first this occur a few days ago, print through the night and this surprise at the morning. At first i tought the print has dropped but then I saw the nozzle digg like 3-4mm into the print (second image red rectangle).
2. happening again 3 day later, I thought it is because the design - it is like wine glass - i have to use brims. But the print again shows some digging. (this was printed many times without problem with same fillament).
3. today the printer was just about find home before print and I heard some wired clicking, the hotend (215°) was actually digging to the surface of the printbed sheet! So i reset it and i saw that left leadscrew is 5mm below the right one (axes shifted). Failure stats are also not very convincing.
I have to say again, 500h without problem. Maybe I'm doing something terribly wrong, is there any way how to diagnostic this? I'm sure that the digging cause the print fall, not the other way. Fillament diameter 1.75x1.76, PLA devil design Violet.
What do you think? Thanks! Michal