What we tested
| File | PrusaSlicer said | Actual problem | Result |
|---|---|---|---|
| T-shaped part: 10 mm stem, 40 mm top bar 30 mm up | Floating bridge anchors, Low bed adhesion, Loose extrusions | Clean solid; both arms overhang 15 mm | Sliced; the arms start in mid-air |
| Same part, supports on | No warning | Clean solid; both arms overhang 15 mm | Sliced with supports (52% more filament) |
| Same part, 5 mm brim | Floating bridge anchors, Loose extrusions | Clean solid; both arms overhang 15 mm | Sliced; the arms start in mid-air |
| Arm with a 2 mm tip hanging 15 mm below it | Long bridging extrusions | Clean solid; the tip starts in mid-air | Sliced; the tip starts in mid-air |
| Same part, supports on | No warning | Clean solid; the tip starts in mid-air | Sliced with supports |
| 20 × 20 × 10 mm block with a second one 5 mm above it | Floating object part, Floating bridge anchors, Loose extrusions, Long bridging extrusions | 2 shells, 5 mm apart | Sliced; the upper block starts in mid-air |
| 40 × 20 × 12 mm block | No warning | Clean solid | Sliced |
What is going on
After slicing, PrusaSlicer simulates where the print would need support and lists each problem it found under the object's name (source). The issue names are Long bridging extrusions, Floating bridge anchors, Collapsing overhang, Loose extrusions, Low bed adhesion, Floating object part and Thin fragile part. "Also consider enabling brim." is added only for Low bed adhesion on an object without a brim.
The warning is advice, not an error: the G-code was exported every time, with the overhangs printed in mid-air. A 5 mm brim removed Low bed adhesion and the brim line from the T-shaped part, but not the overhang names. The floating block also got "Empty layer between".
FixSTL reported all three parts as clean solids and counted the floating block as a second shell; it does not add supports or change the shape.
What was actually wrong
How to fix it
- Find the part named in the warning and look in the preview for overhangs, arms or tips that start in mid-air.
- Turn on supports, or rotate the part so long overhangs face up or lie on the bed.
- For Low bed adhesion, add a brim; in our test it removed that issue and the brim advice.
- For Floating object part, check whether a separate piece floats above the rest; it needs supports or a fix in the model.
- Check the file in FixSTL if you suspect stray pieces: it counts separate shells, but it does not add supports.
Source: Seen in our tests · PrusaSlicer 2.9.6 on macOS