Filament clumping up on nozzle during prints

[Electricfuse 0]

Anyone have any idea why halfway through my prints the filament just starts not sticking to the previous layers and just starts to clump up together around the nozzle resulting in a mound of plastic around the nozzle and a a detatched print? 

[Slashee_the_Cow 284]

Firstly, when you see it start to clump around the nozzle: stop printing, grab the clump (with tweezers or something cause it'll be hot) and remove it. Let it do that too long and there's a good chance you'll clog your nozzle. The chances it'll just hit a patch and start going properly again are pretty much nil.

 

Secondly: there are about half a zillion reasons this can happen, but most of them have to do with height (specifically, the nozzle being too high above the print, or the Z offset being too low). You didn't specify your printer or what sort of thing you're trying to print (or what material, or what print settings), so it's hard to rule anything out.

• Make sure your bed is properly levelled. If it hits a part where the bed is lower, the print will go lower and the nozzle will end up too high. Even if you have a bed levelling sensor, unless you have a printer which does it all automatically (like the Ender-3 SE VE doesn't even have knobs to adjust, it relies exclusively on the sensor) you need to start with it level.
• Make sure your Z offset is set correctly: if it's a little high it'll work to start but the difference can build up. If it's a little low it'll be putting pressure on the filament which might start to build up excess material around the nozzle.
• Make sure whatever control mechanism on your printer for the Z axis (on a lot of printers it's just a stepper motor which spins a tall screw) is at the correct tension. If it's too loose the head could be moving more or less than it should every layer. If you do have the screw kind, make sure it's tight enough that (turn the printer off first so it unlocks the motor) you can turn it by hand and the gantry will move, but if you just wiggle your fingers a teeny bit it shouldn't turn or wobble.
• Check to see if your nozzle is clogged (and clean or replace it if necessary): if it is then the correct amount of filament might not get out and it'll underextrude, giving you layers that are slightly shorter than they be.
• Make sure the steps/mm for the Z axis is correct: if it's wrong your printer won't move up the correct distance every time.
• Print settings: make sure you're not asking too much of your printer (or nozzle especially). If you're trying to print layers too high or lines too wide (or worse, both) for your nozzle, it'll result in underextrusion. If you're using a large nozzle, make sure your hot end can actually heat that volume up enough as it passes through (you might have to turn up the temperature in that sort of situation).
• Model errors: if there's something wrong (either malformed model or poorly designed) somewhere in your model you might have a gap somewhere of a layer or few, if the printer tries printing over that, it won't be able to adhere to anything that far away.