I’m getting increasingly frustrated by blemishes introduced by “gunk” from left-over filament, presumably on my nozzle or somewhere nearby. It happens both with single-colour and multi-colour prints - but it’s more visible with the latter, of course. See pics below. Every now and then, there’s suddenly a small blob somewhere on my print that shouldn’t be there - often with a string attached. Sometimes I see it happen and manage to remove it manually before the next layer, but I don’t think I should be doing this. It happens with different BambuLab filaments, but I mostly print with PLA Matte. I’ve run full calibration twice, tightened the belts and calibrated flow dynamics. I have no idea why/where this stuff accumulates - and obviously no idea, either, how to avoid it. I also don’t think it has anything to do with humidity: when I dried the filament for the recommended number of hours, its weight changed by 0.3 grams (and it was an almost new roll).
H2S, printing with both regular and tungsten carbide nozzles, latest firmware installed…
Reduce flow. Just that. You need to be at the edge between under and over extrusion.
White is a nightmare.
I was used to print a white plate with magenta text. with a 0.2 so approx 20 h print. aborted a lot of them due to even a single micro bit of magenta. Yes I tried to remove them manually but solution was tuning the flow.
please note i also had to print petg at 220°c to avoid that and have a good print (slow)
From what I can tell, the filament is dry. Otherwise it would have lost weight during the drying process? Will start with the lightest colour next time - however, as soon as I get to the next layer and start with white again, there’s gunk left from the previous dark colour, I guess?
Will reduce flow and try again. Or rather, first watch a few videos about reducing flow, I guess.
you just have to reduce that number until you hit the right place. 0.98 try 0.96 and carry on wasting prints until you observe there is no extra plastic around. but then you need to check if it’s under extruding. I really don’t use calibration tests for doing this, I find them misleading and talking about models, every geometry and shape has its very own needs.
if the geometry pushes the device to print very slow details, maybe nozzle’s temperature shouldn’t be capped at filament’s max, right ?
Sure, those are made to find a middle ground, but for me, they’re too small and short to verify the formation of web like strands that develop from constantly going up and down on those ridges like a marathon. with normal prints i don’t bother tweaking too much with retraction but for plates with white especially is a must
You can choose your own color ordering, which can sometimes effect how likely defects are to show, like Gerrit hinted at. One layer of white can conceal very small wisps/imperfections, but you’ll still see big boogers if they get left behind.
One thing to also consider is dust/filament bits being blown around in the printer. If you get a painter’s tack rag and wipe down the insides of your printer you may be surprised. There can be lots of little filament wisps in there that the cooling fans can stir up and allow to fall onto a print.
Besides the other hints here, I just have some extra steps I follow in addition to cleaning the printer. I don’t clean or apply glue to the build plate until I’m getting ready to print. Putting the plate in early just gives time for any activities in the printer chamber to drop fresh wisps and dust onto it to ruin prints.
If space on the build plate allows, a prime tower helps trap any bits left over from filament swaps and purges.
Drying filament well also helps. Wet filament can try to curl as it comes out of the nozzle and can lead to bits being dragged around on your prints. If they attach to the print you get a blem. If they attach to the extruder you can get an encased extruder (example photos in the forum where it has happened to others and it is not fun to clean up).
A dirty printer is the big one and is the main source of embedded blemish issues for me. Once it got a good cleaning the numbers of blems went way down.
OK - I’ve now stood in front of the printer for almost an hour and have a better idea of what happens: the extra filament that gets attached to the nozzle comes from the prime tower. The thin threads of the old colour are created when the new colour is printed on the prime tower - see my third pic in the original post. Some of it stays put, but some of it ends up on the print. The BambuLab prime tower wiki ( Prime tower | Bambu Lab Wiki ) is a bit much for me to digest - any hints on where to start changing things so that the threads are not created?
Looks like I have a real flow problem… This was printed in vase mode - after flow rate calibration. Sigh. I bought the BambuLab printer in order not to have to deal with this kind of crap…
