What we tested
| File | PrusaSlicer said | Actual problem | Result |
|---|---|---|---|
| 40 × 20 × 12 mm block, one square flipped | Auto-repaired 2 errors | 2 flipped faces | G-code identical to the clean block |
| Same block, turned inside out | Auto-repaired 192 errors | All 192 faces flipped | G-code identical to the clean block |
| Thingi10K 1004826 by mz4250 (CC BY-SA) | Auto-repaired 38 errors | Flipped faces, 1 non-manifold edge; FixSTL repaired it to a verified solid | Same filament before and after repair (579.08 mm) |
| Thingi10K 285366 by whpthomas (CC BY-SA) | Auto-repaired 40 errors | 20 zero-area faces, 20 non-manifold edges; FixSTL repaired it to a verified solid | Same filament before and after repair (207.14 mm) |
| Thingi10K 52310 by Typhoon69 (CC BY-SA) | Auto-repaired 5021 errors, then 1334 open edges | 141 shells, 5,742 self-intersections; FixSTL repaired it partly | Sliced with empty-layer warnings from 10 mm up, before and after repair |
What is going on
The count is the sum of five statistics from PrusaSlicer's STL reader: degenerate facets, edges fixed, facets removed, facets reversed and backwards edges (source). A model turned inside out counts every triangle.
100 of the 200 public test files showed it. 43 had no open edges left afterwards, and FixSTL repaired 36 of those to a verified solid. Since 2.4 this repair runs on STL files only, not on 3MF, AMF or OBJ (release notes).
What was actually wrong
How to fix it
- Hover the warning icon. If there are no remaining errors, slice and check the preview.
- If open edges remain, check the file in FixSTL to see whether they are holes, internal walls or a sheet.
- Repair and re-import; the icon should be gone.
- If the count is in the thousands, look for overlapping or loose parts in the layer preview.
Source: Vendor source code · github.com · PrusaSlicer 2.9.6 on macOS