Hi all, I have been on a journey of designing and 3d printing gaskets. This is the first time I have printed TPU. I have a Bambu P1s and am using Bambu TPU 90A filament. At first I had issues with under extrusion around features and excessive stringing using the bambu profile despite the flow dynamics calibration, etc. I started playing around with speeds and referenced some other available successful profiles. I was able to mitigate stringing and am getting smooth results with great extrusion. One problem remains and it are these little nubs left behind on various places in the part. They correlate to the path the nozzle takes when printing. I am going to attach screenshots of the parts and list the settings and what I have tried. I would appreciate any insights for those more well versed in TPU. It is interesting because with PLA and PETG I never had to touch anything speed or retraction related. I figure TPU is one of the more changeling beasts.
- Performed multiple cold pulls, no sign of debris
- Dried: 10+ hours at 70C in Sunlu S4
- Retraction: increased to 1mm
- Speeds: lowered, see screenshots
Those are some pretty clean tpu prints imo. Not much stringing.
I’d just trim them a little bit with a deburring tool.
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How are you printing? Through the back spool holder?
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How are you drying your TPU?
Thanks for the response, wasn’t sure if I was splitting hairs, but I always try for perfection haha.
I am printing directly from the dryer. It is plumbed into the Bambu 4:1 adapter. I am aware there is concern of the force required. I feed it through a very gentle bend, least path of resistance, and I undid the clips on the Bowden tube for the cable chain. I have printed for hours so far and never had the extruder slip from what I can tell. Here is a photo of my setup. The spool is in the front most spot on the left hand side.
In the Sunlu s4 at 70C. I am printing while actively drying as well.
I think that is most likely your issue is that it is getting kinked in the pfte tube. I see that your setup may not fit this, but if you can move things, I printed this, and I havent had a single tpu fail since! https://makerworld.com/en/models/1046490-top-spool-holder-for-x1c-p1p-p1s?from=search#profileId-1032429
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ohhhh.
okay see, tpu doesn’t like ptfe tubes. the A1 series has an advantage because it doesn’t have any turns or curves and you can just feed tpu directly into the machine without a tube if need be,
back in the old days we used to put a couple drops of machine oil/lube on one of those round cotton facial pad things and then use a clip and run the filament through it so it would pick up a small amount of oil to enable sticker/rougher filaments to slide through tubes and go around curves but its become much less of a thing in modern 3d printing times. bit of a tangent but… eh.
personally i would just eliminate most of the ptfe tube when printing tpu and just rawdog that stuff as far as it’ll go before entering the machine on some sort of external spool holder. ideally it’d be from directly above (again, see: advantage of A1 series) but i know that isn’t always feasible.
That is pretty nifty. So if it was hanging up in the ptfe tube, wouldn’t it exibit signs of under extrusion? These nubs seem to be excess filament left behind during traveling. I have enabled a retraction length of 1mm but haven’t messed with retraction speed or anything of the sorts. I also saw other enable wiping but not sure how that would help. Could you explain on what you see exactly and how that could be snagging? I am interested in learning more about the mechanics and such. Thanks!
its less the “snag” and more the “snap back” when the stress on the filament prevents it from stretching any further.
the snag is the problem but the result is that it goes from underextruding for a few moments (and so the printer compensates) and then the filament snaps into position like an elastic band, overloading the nozzle.
so it goes from too little filament to too much filament to too little filament to too much filament.
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Appreciate the response. Similar to below would the filament exhibit signs of under extrusion if it was snagging? Why do you think the nubs are due to snagging? I’d like to learn more. To me it almost seems like leftover filament when traveling despite the retraction height being 1mm. It is weird it only happens at these points.
That makes a lot of sense. How does the printer exactly tell if it is under extruding? I have noticed the spool does not spin as smoothly as hard filament and can spin all at once after tension has built up. I really would like to be able to print from the dryer actively to keep it dry. Do you think running a separate line directly from the dryer down above into the print head would work?
i’m not exactly sure; i know it checks nozzle pressure during its warm-up/calibration sequence but i don’t have details during a print.
its just that tpu when stretched is less filament and then when it snaps back and suddenly has enough filament is generally when things start getting messy.
Appreciate the info, I’ll try direct feeding it with a tube next, if it persists then no tube, etc. Process of elimination.
is it possible to drill a hole in the shelf above and use a couple inches of straight (no curves) ptfe tube and/or a PC4-M6(? is that the right size?) connector/filament buffer so you can just place the spool on a holder on the shelf above the machine and feed it straight down?
Sorry to suggest potentially damaging a shelf via drilling a tiny hole but y’know.
Not a bad idea, I have no issues blasting a hole through it, I bought this thing on marketplace specifically for this setup. It has a big roll up door which is cool too. I could try feeding the dryer through that way as well, then external spool holder if all else fails. I have extra tube but the Bambu tube is better and has a larger ID which results in less friction. The Sunlu tube is narrower.
I wish you the best of luck then!
TPU is one of the more finicky filaments to print with and you seem to be doing quite well for yourself in terms of wrangling it in. There’s loads of people who refuse to touch the stuff.
My only other suggestion is that if you can’t eliminate the curves/bends in the ptfe tubes to maybe consider getting the “TPU for AMS” by Bambu. I’m kind of a frugaly jerk and so ordinarily I wouldn’t suggest such a thing but if you don’t mind that its kinda firm for a TPU then you might have better luck with it taking turns/bends since its, well, designed for an AMS.
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It might, but not very likely. It is probably slowing down slightly in the sharpest part of the bend in the tubing, not enough to stop it completely, but enough for it to cause your issue. Tpu is also prone to that if it is not quite dry enough. I tried printing while drying as well, and it looked awful. Hope this helps!
Gotcha, I’ll try a direct feed as a test. To be clear I dried it in advance, then continued to run the drier while printing as it is very hydroscopic and could begin to pick up moisture even after an hour. My hours is stays pretty humid 53-56% thanks to oversized AC.
