Brown bits appearing in white PETG print
Hi all,
My week-old self-assembled Core One+ is my first 3D printer, and I've started printing PETG. However I seem to get a few occasional wisps of what looks like brown burnt material appearing and I'm not sure what's causing it. Has anyone seen this before?
It's not so bad in the above photo because it's outside the model so I can just pull it off with tweezers, however sometimes there's a large lump of it and it gets squashed into a layer so I end up with a brown bit in one of the layer lines which looks weird on an otherwise all white object.
It almost looks like it's burned and the PETG has discoloured, however I'm using the Buddy3D PETG profile in Prusaslicer which apparently contains all the correct settings for this particular filament. I tried lowering the nozzle temperature by 10 degrees from 255 to 245 but it didn't seem to make any difference. The filament doesn't seem to be dirty, although it did arrive with a tear in the bag (no damage to the box, so the tear happened before it was packed) so perhaps some dirt has gotten in? I've printed about 200g of the 2kg spool so far, so you'd think any dirt or dust would be on the outer layers of the spool, which have long been used up, yet it still happens.
On a recent print I got quite a large brown piece come out, and I happened to be watching so I could remove it with tweezers before it was embedded into the next layer, but it was way more than you'd expect from the amount of plastic normally extruded (maybe 4cm long and looked like 3-4 strings tangled together, similar to the above photo's two strings). It's almost like it was build up from somewhere but I can't see where it would be accumulating.
I have printed a few PLA models and haven't seen anything like that with PLA. I haven't tried any other PETG spools yet, only this Buddy3D White one.
Has anyone seen this before, and knows what the cause might be?
RE: Brown bits appearing in white PETG print
You may need to clean your print path. When I purchased my printer, I was advised to purchase cleaning filament as well. Going from low temp filament to high temp filament can cause issues. A cold pull or a higher temp purge may help you.
White filaments are often tricky to print because of the high pigment load, this can cause strange issues when the melt becomes non-newtonian. Are you getting some stringing? Stringing can adhere to the nozzle and overcook for a while before dripping into the workpiece,
A torn bag suggests that filament drying is even more important than usual and moisture causes stringing too.
I suggest you reserve the white for non critical prints for a while and use darker colours while you learn the ropes.
Cheerio,
RE: Brown bits appearing in white PETG print
I am getting a little stringing but it's not particularly significant. I think you are right though and it is probably overcooked strings causing it. It's just a bit strange because I'm not missing any layer lines anywhere on the printed model so I'm not sure where the 'extra' filament is coming from.
I don't think it's a print path issue because it doesn't seem to happen with other filaments, just this white PETG from the torn bag.
I bought the white PETG cheap on sale to use for non-critical prints so it's not a problem, I was just wondering what was causing it.
RE: Brown bits appearing in white PETG print
I had this happen again after changing filaments and this time the 'brown bit' was the same colour as the previous filament. I noticed that some of the previous filament was stuck around the sides of the nozzle tip, so what I think is happening is that filament is building up around the sides of the nozzle tip during printing, overcooking, and then at some point it comes loose in a blob and lands on the print.
I'm not sure what the solution to this is, other than keeping the filament dry if it's a humidity issue. I don't have any way currently of keeping the 2kg spool of white PETG dry and I'm now noticing that after purging the nozzle at the start of the print, it always leaves a long string when the print head moves from the edge of the sheet to the middle to start the print. I'm assuming this increase in stringing is because the exposed filament is absorbing moisture, which I kind of expected given the high humidity where I live.
I have some USS Dryboxes on order so hopefully once those arrive it will become less of an issue over time.
RE: Brown bits appearing in white PETG print
I have the same fine hair-like strings and just ignore it. If it gets worse, I'll dry the filament. I do use a brass brush on the nozzle to remove any build-up, but probably not as often as I should.
RE: Brown bits appearing in white PETG print
Yeah it wouldn't bother me so much except sometimes they get embedded into the print and at best is looks bad, at worst it creates a weak point. For prototypes it doesn't matter but for finished products it's a bit annoying having to reprint a few times to get one without any defects.
I will try to remove the build up but it never builds up very much from my casual observations, and I have started prints with a clean nozzle before and ended up with these things embedded in them so it seems to accumulate enough to deposit a few times during a print, maybe once every hour of printing at a rough guess.
RE: Brown bits appearing in white PETG print
I found storage bins that have seals on the lids. A couple of 4mm quick connects, some tubing and built a dry box for TPU. It can hold 3 1KG spools. Cost about C$25. Some activated alumina desiccant and all is well.
I store all my filament in sealed storage bins in an effort to keep them dry and I live in a dry area. A friend keeps all his spools in their own dry boxes. Look at local shops for a storage bin that has seals that can hold what filaments you print with regularly. Tubing and quick connects can be purchased at a farm dealership or some hardware stores. You can order kg's of activated alumina from AliExpress for a low cost. I use stainless steel infusers to hole the activated alumina so I can just throw them in the oven when I need to recharge them.
I still recommend some cleaning filament. You may find that it is removing material that is stuck in your head. If I am printing something that needs to look good, I run some through my printer and get the gunk out.
RE: Brown bits appearing in white PETG print
It must be humidity because it's getting worse. Had two failed prints in a row because it dumped such a big wad of plastic that the next time around it knocked the whole extruder off course:
Third time I watched it and picked the gathering plastic off the hot end tip a few times during the print, except for once where it got deposited on the print - but luckily I could pause the print and bend it out of the way, so the print succeeded and I was only left with a nub sticking out that I could cut off after the print was finished.
Unfortunately being a 2kg spool it's not so easy for me to dry out but perhaps once I get my first empty spool, I'll wind 1kg of this white PETG onto it and then try to dry that out, and keep it in one of the USS Dryboxes that arrived a couple of days ago.
Thanks for the suggestions - I don't think it's anything inside the print head itself, because I recently tried a bunch of different filaments (ordered a heap of samples from Prusa) and they all printed perfectly fine without any issues at all. I think it's just this particular Buddy3D white PETG and the fact that it has been sitting exposed for a while in a high humidity environment.