What makes a Prusa lose its z-height calibration?
Working with a Prusa MK3s and it works fine most of the time. I was using it yesterday morning and it was doing OK, then it crashed on a job, some pieces lost adhesion and everything else I tried failed in the same way. Loose, stringy first layer, no adhesion at all. I have cleaned/scrubbed/sanded the print bed to surgical grade, and made a couple more attempts this afternoon. It seems to be working now after a bit of Live Z adjustment but I find it baffling that this all comes down to eyeballing a moving object. If the PINDA is set right, shouldn't there be a programmable offset for the print nozzle used on the material or other specs?
Anyway, I am trying to work out where the problem is here, if it's the print bed heat being unstable (yes, I use an IR gun and no, it's not wrong, because I am not using it to get exact temps but to verify that heat is uniform across the print bed, not varying from 60°C to 40 something, as this one does), or if it's the material not being laid down properly/poor Z-height. My luck, it could be both.
I expect that a properly setup machine should just run, not lose Z-height calibration, but my first layer tests after working on the print bed told another story. I still have no idea what a good result is for that…90° corners, yes, but that last part: should it be a solid or should I see lines of filament/gaps? I'd rather see something that made it clear.
So what is going on here? This is a school machine I brought home to sort out, as it was having the same problems there and no one had the bandwidth to deal with it. Not sure I do after a couple of weeks of this.