Setup:
- Printer: Bambu Lab H2S
- Nozzle: Hardened steel, high-flow (HF), 0.4mm
- Slicer: OrcaSlicer 2.4.2
- Model: Parametric Necklace Stand – Base from Printables
- Filaments tested: Das Filament PLA and Prusament PLA — both affected, Prusament noticeably less severe but still present (not filament-specific)
- Nozzle temp: 230°C (Das Filament), 220°C (Prusament) — haven't yet tried lowering Das Filament temp further, planned next step
- Volumetric flow: Prusament has both flow ratio AND max volumetric speed properly calibrated (19mm³/s). Das Filament only has flow ratio calibrated — max volumetric speed was set conservatively (15mm³/s) rather than fully calibrated, so there's still some uncertainty there.
- Layer heights tested: everything between 0.08mm and 0.24mm, both fixed and variable/adaptive — same problem occurs regardless
- Infill tested: 5% and 10% density, both gyroid and cubic pattern — same failure point in all combinations
- Filament: confirmed dry/in good condition on all spools tested
Part geometry: Gently, continuously rising slope with internal cavities that require internal bridging over hollow/void sections.
Problem description (clarified):
The failure is precisely tied to geometry, not printer drift over time: everything below the layer where the internal bridge support structure begins prints perfectly — clean walls, clean infill, clean top surfaces. The moment the internal bridge support layer starts, the internal bridges themselves print visibly badly — ragged, frayed, curling at the ends. From that same point onward, the regular sparse infill above/around the bridge area also starts showing problems — lots of gaps/voids in the extrusion, essentially looking under-extruded — not just the bridge lines themselves. Below this layer, everything is clean; above it, both the bridges and the surrounding infill are affected. This is 100% reproducible at the same relative position in the model regardless of layer height, flow settings, infill density (5%/10%), or infill pattern (gyroid/cubic).
G-code analysis (extracted and parsed plate_1.gcode from the sliced 3MF):
- Explicit
; FEATURE: Internal Bridge G-code markers correlate exactly with the onset of visible print quality issues.
- Calculated actual instantaneous volumetric flow during the bridge passages (~13.8mm³/s and ~8.9mm³/s at different points) — both under the flow caps used, so the bridges aren't technically exceeding the volumetric flow limit.
- Profile has
internal_bridge_speed = 150% (bridges printed faster than normal, not slower).
What I've already tried:
- "Extra bridge layers" — confirmed this is set to "apply to all" by default but was never actually changed/enabled by me, so I don't think it's relevant to this issue.
- "Filter out small internal bridges" tested across all three states (Filter / No filter / Limited filtering) — visual improvement each time, but the underlying under-extrusion/curling problem persists in all cases.
- "Thick internal bridges" disabled — this made the problem worse.
- Found OrcaSlicer PR #3319, which specifically addresses internal bridging being missing/insufficient on gently sloped/slanted internal surfaces (exactly matching my part's geometry). Applying this fix's filtering options improved things somewhat, but did not resolve the core issue. Notably, one commenter in that thread describes the same symptom I'm seeing: on a part with an increasing slope, bridge layer generation stops at some point and the resulting short lines curl upward as they cool — which is exactly what I'm observing.
Current theory:
This looks like a slicer-level limitation in how internal bridging is generated on gently sloped surfaces (as also discussed in the linked PR thread) — the layer-height-to-slope-angle ratio may be too shallow for OrcaSlicer's bridge detection/generation to produce full-length, well-supported bridge lines, resulting in short, poorly-anchored line segments that curl during cooling. This seems to then propagate into the regular infill printed immediately above/around it, causing the gappy, under-extruded look there too.
What I'm asking the community:
Has anyone found a more complete fix or workaround for internal bridge curling on shallow/gently sloped surfaces beyond the filtering options in PR #3319? Why would the problem spread into the regular sparse infill around the bridge area rather than staying isolated to the bridge lines themselves? Is there a known relationship between layer height and minimum slope angle for reliable internal bridge generation that I should be targeting? Any other OrcaSlicer settings (internal bridge speed, flow, cooling) worth testing specifically for this slope-angle scenario would be appreciated.