I’ve been trying to address this underextrusion issue with not a whole lot of success. As far as I can tell it’s a slicer or bambu hw/fw issue when going around corners.
I created a simple I-beam model which I’m printing without top layers so I can easily see the wall layers. In the “long” straight sections (the whole thing is ~35mm long) the extrusion is good, but when going around corners there are gaps similar to those seem in the photo above.
Here is what 3 samples look like (ignore the black dots, they’re an attempt at getting the camera to focus on the samples instead of on the background):
- left sample: ASA, 0.6 nozzle, “0.3mm strength” preset
- middle sample: same except that one half has a modifier with “flow ratio: 1.2”, I can’t tell which it was, i.e., not effective
- right sample has a modifier for the lower half with all speeds reduced to 10mm/s and it looks significantly better to me
The 3mf file for the right two samples is available for download
It seems to me that there’s a real problem when the walls go around corners and it seems to me that the print head needs to briefly slow down to allow the filament to actually fill the corner. Looking at it more precisely, these walls are laid down going counter-clockwise around the shape and it looks to me like the gaps are just before the actual corner. I suspect that the movement after the corner pulls the filament that was extruded before the corner across the corner in a diagonal. Dunno whether this is a slicer or firmware issue.