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I could have sworn I read somewhere that when printing with TPU to make sure the part cooling fan is blowing. But I just did a quick Googling and couldn't find anything stating such on Matter Hackers or All3dp.

I currently don't have a part cooling fan attached (waiting for square nuts to come in). I've been able to get by printing PLA without the fan. I'm curious if this is going to be a major obstacle with TPU.

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  • $\begingroup$ In my experience printing PLA without cooling is an utter mess of warping/curling corners, so my guess would be that if the stuff you're printing is such that you're happy without a fan for PLA, you'll probably also be happy without a fan for TPU. But I haven't printed with TPU yet (just modified-PLA flex materials) so I don't think I'm qualified to give a real answer yet. Incidentally I have my first roll of TPU arriving tomorrow to play with, so if I find anything interesting I'll post an answer for you afterwards. $\endgroup$ – R.. GitHub STOP HELPING ICE Jan 23 at 22:05
  • $\begingroup$ By the way, you could just print the square nuts you need to attach the fan....except that you're going to have a hard time printing that kind of detailed part in PLA without a cooling fan. 🤪 $\endgroup$ – R.. GitHub STOP HELPING ICE Jan 23 at 22:06
  • $\begingroup$ TPU seems to need about as much cooling as PETG in my experience: A bit doesn't hurt, but none is also just fine. $\endgroup$ – towe Jan 24 at 7:16
  • $\begingroup$ My preliminary result with TPU seems to be that you want low cooling fan, if any, so you're probably ok without it. Too much fan seems to preclude not layer bonding, but bonding of adjacent wall lines. I'll follow up with a real answer after more testing though. $\endgroup$ – R.. GitHub STOP HELPING ICE Jan 24 at 21:26
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You'll probably be fine printing TPU with no fan. I just started printing with TPU, and did a lot of test prints to find out what settings work. Fan made little difference. With hotend at 230 °C, which I started out with, 0-20% fan was fine. I eventually increased temperature to 250 °C, which made extrusion more consistent and allowed me to reduce linear advance K-factor somewhat, and at that temperature having a bit more fan (I'm using 40% now) seems to help the material hold its shape, but it mainly made a difference at higher print speeds (over 35 mm/s) where the motion of the nozzle was "pulling on" the still-very-soft material just extruded. At 30 mm/s and below, fan still doesn't seem very important.

All of this is likely to vary somewhat with the properties of your machine. However I think it's safe to say you should be able to find a combination of print speed and temperature that make it possible to get by with no fan.

Follow-up: Upon further experimentation with TPU, I would say you really don't want any fan at all, except possibly for bridges. I've found significant distortion to shape just from air pressure from the fan, and at higher speeds the fan makes the print brittle just like what happens with PETG. Layers of TPU really seem to want time to melt together to bond, and without a fan blowing on them they don't seem to lose their shape during that time.

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  • $\begingroup$ This is pretty consistent with my first print too. The only real problem I had was with bridging. The file (a phone case) has two gaps to bridge for the charger and mic hole. I assume that once I set up cooling those bridges will be better. $\endgroup$ – Lux Claridge Jan 27 at 14:20
  • $\begingroup$ @Lux: Same problem here. ~40 mm bridge was good, only one string drooping. Credit card length bridge did poorly though. Probably should experiment with supports & use Cura's support tree to handle these bridges. $\endgroup$ – R.. GitHub STOP HELPING ICE Jan 27 at 16:03
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Sharing fan percentages like in this answer is only helpful if you use the same printer model, cooling fan and cooling duct. As there are many 3D printers and many cooling fans, ducts and solutions, this cannot be readily adopted to every 3D printer.

So, in such a case I would rely on the manufacturers of the filament e.g. the flexible filament I use has settings for different printers listed here. TPU is not very prone to warping. The general rule for cooling of TPU is found to not use it for the first 2 layers and after that proceed with a moderate cooling flow. What that value is for your printer is left as an experiment. Several test/calibration print designs exist (e.g. for bridging) to test this out. It is said that a little cooling aids in better aesthetic prints (finer details) while less cooling results in stronger layer adhesion and thus stronger prints.

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