Overlapping inner perimeter walls when scaling the model

[davidshin172]

Version

2.2.0

Operating system type + version

Arch Linux

3D printer brand / version + firmware version (if known)

Ender 3 + SKR Mini E3 v1.2 + Marlin 2.0

Behavior

• There seems to be a certain scaling percentage where inner permiter walls end up overlapping: In the above image, there are two inner perimeters that overlap (As signified the "ridge" in the middle). This causes the wall area to be thicker than intended, leading to a bulge like so (This is at 68 percent): I managed to catch the printer going around the wall 4 times per layer, so it doesn't seem to be a visual artifact.

Steps to Reproduce

1. Open attached project file.
2. Note that the object is scaled at 75%.
3. Slice the object.
4. Note that the inner perimeters on the top layers are overlapping.
5. Turn scale down to 67%.
6. Note that the area previously covered as inner perimeters are now gap fills

Project File (.3MF) where problem occurs

overlap.tar.gz

[davidshin172]

Here's the 67% one: Note the lack of bulge in the wall area (Bulge at the bottom is something I'm dealing with for this printer).

[ssill2]

The bottom bulge on this is not particular to the any printer as I understand it. The issue is documented heavily here:

https://forum.prusaprinters.org/forum/original-prusa-i3-mk3s-mk3-how-do-i-print-this-printing-help/buldge-when-print-reaches-solid-layers/paged/1/

I'm really hoping this gets some attention.

[mikeev261]

Still seeing this happen in PrusaSlicer 2.5.x and now 2.6.x.

Usually occurs with a layer change such as when infill stops, or there is a gap held up by supports (as others have noted):

Here's an example: