Started printing this filament shrinkage test and had to leave the house. When I came back, the whole upper half of the part had shifted after the first few layers, and it left two solid blobs attached and one ball of spaghetti. The magnetic bed doesn’t appear to have moved. Part is still solidly adhered to the print bed. How did this happen, and how can I keep it from happening again?
You say you cleaned the nozzle, did you do a cold pull? Sounds like a potential clog.
Why would it be a clog if they’re over-extruding?
Not entirely sure what “cold pull” means. I unscrewed the nozzle while the machine was powered off and the hot end was room temperature. Blasted the living hell out of the nozzle with a small torch, scrubbed it inside and out with a brass bristle brush, ran one of the bristles through the end of the nozzle. With the nozzle and ptfe out, I heated the hot end to 60 C to loosen the remaining chunk of filament and pushed it out the bottom with the handle of a needle file. It came out in one solid piece. Shined a light through both hot end and nozzle individually and it looked clear.
Cold pulling is where you heat the hot end up to just past the melting point of your filament and push a bit of filament through it by hand until an inch or so comes through, then you cut the heat and let the nozzle cool down a bit, then pull the filament back through the extruder side.
This basically traps all the little bits of semi-melted plastic left behind from previous prints, and pulls them out as one big glob.
Different guides will give different advice about the temp to cool to, but basically you want it cool enough that it puts up meaningful resistance pulling the filament back out by hand but isn’t impossible.
You should probably do this on some routine, but at the very least after any clog and when you get print errors that you can’t immediately diagnose. Partial clogs are responsible for way more issues than you might think.
Did you hot tighten the nozzle while putting it back? Don’t think it caused your current failure, but cold tightening can lead to more clogs in the future.
I think layer shifts can be caused by many different things, but the first thing I’d check is that the bed carriage can move freely and there isn’t something mechanically blocking it, like a wire or a misplaced screwdriver. The second thing I’d check would be the belt and gears, so that the bed can’t move without the stepper motor also spinning.
You unscrew your extruder, heat the hotend up until you can barely push the plastic across (~170ºC for PLA, ~180°C for ABS), push a bit of it and then pull it out.
Cut the end of the filament and do it again, a few times.