Sudden Y axis misbehavior
I've had my MK3S for a couple months now, and it has worked beautifully, but over the weekend it suddenly started acting weirdly. The first thing that happened was that in the middle of a print the carriage suddenly rehomed itself and started printing in mid-air. After that I noticed the purge line was in the wrong place (on the front border of the grid on the bed, not on the dotted line in front of it). A self test failed on Y axis length. After going around the printer tightening up frame screws, I got it to recalibrate and it completed the next couple prints. However, tonight, I noticed the purge line was in the wrong place again, and auto-home isn't landing in the right spot... it's about 10-15mm too far to the rear. I attempted a self-test and it failed on Y axis length again.
I tightened up the screws on the y axis motor gear but that didn't make a difference.
What might be wrong? I've seen reports of Y axis issues on first-run, but this is a sudden development. The Y axis has always been rather loud on rapid movements, but has behaved fine until now and I assumed that was normal.
Re: Sudden Y axis misbehavior
I suspect a idler pulley rubbing on mount or developing bad bearing.
There is strong temptation to leave the belt connected while checking, but that can hide substantial amounts of resistance.
Check by disconnecting belt from y-carraige. Hold the two ends of the belt in your hands and run it back and forth through the idler. Feel for any catcheing. Trying to do this with things connected makes it harder to feel resistances of interesting. While belt is disconnected is also best state to check y-carriage free motion.
Re: Sudden Y axis misbehavior
Hmm. It's an enormous pain to reattach and retension the Y-belt, but I'll do it if it seems necessary. I'll probably contact support tonight to troubleshoot. I presume this is something they've encountered before.
I suspect a idler pulley rubbing on mount or developing bad bearing.
There is strong temptation to leave the belt connected while checking, but that can hide substantial amounts of resistance.
Check by disconnecting belt from y-carraige. Hold the two ends of the belt in your hands and run it back and forth through the idler. Feel for any catcheing. Trying to do this with things connected makes it harder to feel resistances of interesting. While belt is disconnected is also best state to check y-carriage free motion.
Re: Sudden Y axis misbehavior
Sorry it is a pain. Usual method requires pulling the head bed. Better alternative (but a bit late now that your printer is already on the fritz) is to flip the entire machine to service the belt.
This stand works nicely. Makes Y-belt maintenance and adjustment super easy.
https://www.thingiverse.com/thing:2386065
Maybe you can cobble together the equivalent of tow of them.
Re: Sudden Y axis misbehavior
Support suggested that I remove the belt anyway to check the pulleys. The pulleys were fine, but while I had it apart I noticed that one of the heatbed cables somehow got caught between the bed and the left side smooth rod. I think that was making the motor work harder and thus confused it. I've zip tied it out of the way (loosely so it doesn't pull too tight) and I'm recalibrating/testing now. Crisis probably averted 🙂