Repair an STL file for 3D printing
Drop the model and it is repaired straight away: holes closed, flipped triangles turned the right way, duplicates and loose sheets taken out, overlapping parts merged. The open edges are shown in red before the repair, and Undo brings them back if you want to look.
Saves model files for your slicer, never printer code. Opened and sliced in PrusaSlicer, OrcaSlicer, Bambu Studio and Cura.
What gets fixed
Holes in the surface, triangles facing inwards, edges shared by three or more triangles (the slicer’s “non-manifold edges”), triangles with no area, the same triangle stored twice, inside-out parts, thin sheets with no volume, and parts that overlap one another. Small gaps where triangles almost meet are closed too — but only when they are there: a model without gaps is joined exactly as it is, so nothing that was right gets moved.
Why it keeps the shape
Many repair tools rebuild the model out of tiny cubes and wrap a new surface around them: holes close, but corners round off and the file grows. Here the holes are filled along their own edges and the rest of the surface is left where it was — on a test sphere with 338 holes and 1,623 flipped triangles, the repaired volume matched the undamaged sphere to within 0.00001 %.
Checked by a slicer
The repair was tried on 20 real broken models from the Thingi10K research collection, four for each kind of fault, and every result opened in PrusaSlicer. 17 came out with no errors at all, confirmed by PrusaSlicer and by our own edge count; in the other three, parts still touch along an edge — saving as 3MF keeps them correct.
Questions
- Fix model is greyed out in Bambu Studio on my Mac.
- Bambu Studio repairs models through a Windows-only service, so on a Mac it only links to an outside website, and on Linux there is no repair at all. Repair the model here, save it as 3MF or STL and open that in the slicer — it works the same in any browser on any system.
- STL or 3MF after the repair?
- Either opens in every slicer. 3MF stores the model exactly as it is on screen; STL stores only the corners of each triangle, so where two parts touch along an edge a slicer can read them as joined. When that happens you are told, and 3MF is the safe choice.
- My slicer still says there are errors.
- Write to us with the slicer’s message — and try saving as 3MF. Some slicers also count “errors” they have already fixed themselves on loading.
- How big a model can it repair?
- A model of 300,000 triangles takes about three seconds on a laptop. Larger ones work too; the limit is your device’s memory, not ours.