I’ve been trying to print some things in TPU, using a fairly soft 85A TPU, and I keep having under extrusion.

I’ve already reduced speeds to max 25mm/s, and reduced retraction. My printer uses a direct drive extruder, and as far as I can tell, it’s grabbing the filament just fine. I’m printing at 240°C, using my default 0.4mm volcano CHT brass nozzle.

  • @bigredgiraffeEnglish
    6•8 months ago

    Make sure your filament roller doesn’t have too much resistance as well. Since TPU stretches linearly way more than any other filament if it does have a lot of resistance then the extruder won’t be able to pull more filament until it overcomes that resistance and the stretch and it ends up physically thinning out the filament. Just a thought, hope it helps!

    • @nezbyteEnglish
      3•8 months ago

      Great tip! I spent a long time chasing issues with TPU only to realize the spool to extruder section was the culprit. Bypassed the runout sensor and put the spool on bearings to fix the issue.

    • @[email protected]OPEnglish
      1•8 months ago

      Yeah i noticed that right away, it’s sitting on a roller with bearings, not sure I can give it any less resistance without actively unwinding filament as it’s used.

  • [email protected]English
    3•8 months ago

    It’s been a while since I last printed TPU.
    I think I’ve always had to set a slightly higher flow rate for TPU, probably because it always compresses a bit when pushed by the extruder.
    My TPU roll printed somewhat colder than yours at about 220C.
    I usually start with a very low speed (15-30mm/s), retraction completely off, cooling fan very low (25%).
    Tune the flow rate and speed then add a tiny amount of retraction (<1mm).

    YMMV

    • @[email protected]OPEnglish
      2•8 months ago

      I completely forgot about flow rate, increasing that completely fixed the issue. Thanks!

      • [email protected]English
        1•8 months ago

        Great! Good to hear.
        Don’t forget to turn it back down with less springy filaments.

        • @[email protected]OPEnglish
          2•8 months ago

          I have seperste filament profiles for everything, so these changes only affected my “TPU 85A” profile

    • [email protected]English
      1•8 months ago

      I always kinda hated printing with TPU, it was am absolute nightmare on my old printrbot.
      It’s much less so on my prusa, but I’m still used to avoiding it whenever I can.

  • sylver_dragonEnglish
    2•8 months ago

    For me, completely disabling retraction helped out a ton. It went from a stringy mess to mostly clean prints. Other than that, slow speeds and finding the right temperature for my printer/filament got my prints pretty nice.

  • FuglyDuckEnglish
    2•8 months ago

    zero retraction, dry the filament out (If It’s not a short-notice print, I’ll dry it out in a food dehydrator the night before, timing it so it comes out just as I’m starting the print.). Slow it down. Slow it down some more.

    If the under extrusion is constant, try checking the filament’s diameter on the roll, if that’s fine, try upping the flow just a bit. TPU is fairly squishy and stretchy at the same time, so it may need tweaking. Also, consider running a temperature calibration tower.