ASA print failure - part shrinking?

Bambu Lab H2 Series Bambu Lab H2C
1

Hey everyone,

Running into a weird one on my new H2C and hoping someone here has seen it. Printing a simple case in Bambu Lab ASA on the right 0.2mm nozzle, door closed, using glue stick on the textured PEI plate. The exact same model slices and prints perfectly on my X1C, but on the H2C the first chunk of layers comes out noticeably narrower than the walls above them, there’s a clear step where the part suddenly jumps out to the correct dimension. See attached pics (printed part vs. slicer rendering).

A few things I’ve already considered or ruled out:

  • It’s not corner lifting / bed adhesion. The brim and floor are firmly stuck down with glue, no curling.
  • It looks dimensional, not cosmetic, the walls really are inset relative to the bottom.
  • The X1C runs the same sliced file (well, same model, X1C profile) without issue, so the model itself is fine.
  • Using the stock H2C ASA profile for the 0.2 right nozzle in Bambu Studio.

My current guesses are either ASA shrinkage from too much active cooling on the H2C (aux fan + chamber circulation) before the next layer can lock things in, or some line width / initial layer setting in the H2C profile that differs from what the X1C uses. But I’d love to hear from anyone who’s actually printed ASA on the H2C right nozzle at 0.2mm and what their settings looked like.

Anyone seen this before? Any settings you’d recommend tweaking first?

RENDERED:

caseRendered
caseRendered1272×729 263 KB

PRINTED:

casePrinted
casePrinted655×478 134 KB

casePrinted_01
casePrinted_01727×453 48.6 KB

Thanks!

2

Thats a lot of hull lineage right there! I am assuming that’s a high wall count/high infill?

I had it recently on my H2S in ASA, where the hull line looked like that printing a huge part with very high infill and a large wall count.

3

I am using 0.08mm High Quality on both H2C and X1C, 4 wall loops, 15% sparse infill density and infill / wall overlap, All the default settings except for the support, normal (auto) and snug.

Here’s how the X1C printed:

X1C_print_3
X1C_print_3869×1199 261 KB

X1C_print_1
X1C_print_1416×902 82.4 KB

X1C_print_2
X1C_print_2264×698 28.1 KB

4

The differences between the 2 are a heated chamber, and possibly a lot of other profile settings.

the huge deviation comes from the flat surface in the part (hull line as @dann2707 already mentioned). The bridging over the infill including the additional cooling that is required because of the heated chamber brings a lot of stress there.

If you look at layer times, there is a lot of difference there.

The heated chamber and increased cooling are the main differences between the two printers causing this difference.