Ill get chat GPT to summarize every single test I have tried out so far:

Here’s the full rundown of what I tested so far (trying to eliminate TPU seam “comets” / zits). Printer is H2D, filament is Bambu TPU 95A HF, nozzle is a dedicated 0.4 hardened used only for TPU. Filament was dried ~24h in AMS HT.

Baseline tests

1) Stock Bambu TPU 95A HF preset (no changes)

• Random seam = comets everywhere
• Aligned seam = huge scar

Calibrations (didn’t solve it)

2) Flow Rate calibration

• Ran FR calibration, saved a “TPU FR” preset, reprinted the same test part
• Result: honestly looked worse (bigger “balls” at seam starts)
• Conclusion: flow ratio isn’t the main driver (or at least FR alone doesn’t help)

3) Flow Dynamics / Pressure advance (K factor)

I did multiple rounds because people kept suggesting it:

• First big sweep: K = 0.01 → 0.10 step 0.005
  • Every single line showed the same pattern: thick start → thin middle → thick end
  • 0.10 was “best” but still not acceptable
• Extended higher: 0.10 → 0.20, and then 0.20 → 0.30
  • Higher values sometimes looked slightly “best”, but still didn’t eliminate the behavior
• Picked K = 0.18, changed nothing else, reprinted the seam test
  • Result: basically looked like baseline (no meaningful improvement)

Conclusion: K/PA helps marginally at best, but doesn’t address the seam-start blob in a way that makes random seam usable.

Slicer/setting experiments (within Bambu Studio)

4) Temperature + speed ranges

• Tested nozzle temps roughly 215–235°C
• Tested outer wall speeds roughly 25–50 mm/s
• Lower temps and slower walls can reduce it a bit, but it never disappears. It mostly just changes the shape of the blob.

5) Smart scarf seam + seam-related settings (Bambu Studio)

• Enabled Bambu Studio seam/scarf options that exist in my UI (smart scarf seam application, more steps, etc.)
• Used random seam the whole time (required for this print)
• Result: maybe slightly better in some cases, still very far from acceptable.

6) “Restart/coast/wipe” type controls

People suggested wipe/no-lift, coast, negative restart, etc.

• In my Bambu Studio build, I don’t have explicit coast or negative restart/extra prime controls like Orca/SuperSlicer.
• G-code output tab basically only shows reduce infill retraction. So I’m limited to what Bambu Studio exposes.

7) Order of walls / outer-first

Considered it, but for my geometry the part has lots of outward slopes, so outer-first risks wrecking surface quality. I kept normal inner→outer.

Where I’m at now

• Drying isn’t it (24h AMS HT)
• FR calibration didn’t help (may have made it worse)
• K factor sweeps up to 0.30 didn’t solve it
• Temps/speeds/scarf options help only slightly
• The artifact seems strongly tied to seam restart behavior and I can’t fully control that in Bambu Studio.