Mesh Repair & Conversion
Fix non-manifold meshes, convert formats, and prep STLs for slicing.
The downloaded STL with holes, flipped normals, or impossible geometry — the slicer will either crash or print mush. Mesh repair tools sit between Model Libraries and your FDM Slicer. For format conversion (STEP↔STL, voxelization, decimation) the same tools usually do double duty.
Repair / heal automatic
- ★ Microsoft 3D Builder — free, Windows; one-click "repair" that fixes ~80% of broken STLs in seconds. The fastest path when an STL won't slice.
- ★ PrusaSlicer / OrcaSlicer "Fix through Netfabb" — Windows-only built-in repair (calls into Netfabb's free service). One menu click, surprisingly effective.
- Microsoft Print 3D Repair Service — older API behind PrusaSlicer's "Fix through Windows".
- Netfabb Free (Autodesk) — closed source, free desktop tool retired in newer versions; Netfabb online still works through PrusaSlicer.
- MakePrintable — closed source, paid hosted service; useful when desktop tools fail.
- Formware Repair — niche, paid; very capable on hard cases.
Manual / power-user mesh editing
- ★ MeshLab — open source (GPL); decimation, smoothing, boolean cleanup, coordinate transforms, scientific-grade filters. The default FOSS heavyweight.
- ★ Blender — open source (GPL); Edit Mode + 3D-Print Toolbox add-on (built-in) gives you manifold checks, intersection detection, hole filling. The most-used "I'll just open it in Blender" tool.
- Meshmixer (Autodesk) — closed source, free, abandoned in 2021 but still works on Win/Mac. Selection-based smoothing and hollowing remain unmatched for some workflows.
- Plasticity / Fusion 360 — direct-modeling solids; convert mesh to BRep where possible, then heal as a solid.
- 3-matic (Materialise) — paid, professional, medical/dental; mentioned for completeness.
- ZBrush / 3D-Coat / Mudbox — paid sculpting; power tools for organic mesh repair.
STL ↔ STEP / parametric conversion
- ★ FreeCAD Mesh → Shape workflow — convert STL to STEP in FreeCAD via the Mesh + Part workbenches (approximate, not parametric, but usable). Free.
- CADExchanger — paid (cheap one-time), accurate STL↔STEP / IGES / X_T conversion.
- Fusion 360 "Mesh to BRep" — closed source; works well on simple meshes; limits on triangle count in personal use.
- Online: imagetostl, anyconv, Convertio — quick web converters; data-privacy concerns for proprietary models.
Decimation / simplification
- MeshLab Quadric Edge Collapse Decimation — gold standard.
- Blender "Decimate" modifier — fast, good results.
- gltf-transform
optimize— for glTF/GLB pipelines; see 3D / WebGL. - Simplygon — Microsoft's mesh-simplification SDK; commercial.
Format & sanity utilities
- ★ admesh — open source CLI; STL repair, scaling, mirroring, format conversion. Tiny, fast, scriptable.
- stl2pov / stl2off / stl2obj — single-purpose CLIs for batch jobs.
- Open3D — Python lib; programmatic mesh I/O, registration, filters.
- PyMesh, trimesh — Python mesh-processing; common in CAD/CAM scripts.
- MeshLib (Python) — actively developed Python mesh ops; modern alternative to PyMesh.
Resin-specific mesh prep
- ★ UVtools — open source; resin-side mesh-and-layer fix-up. See Resin Slicers.
- Lychee / ChiTuBox auto-repair — built-in repair pass before slicing.
- Meshmixer "Make Solid" — old workflow but still common for hollowing miniatures before resin.
Boolean / CSG operations on meshes
- ★ manifold — open source; the modern fast mesh-boolean library, used as a backend by JSCAD, OpenSCAD experimental, Onshape, and others.
- libigl — research-grade C++/Python mesh booleans.
- CGAL — heavyweight; underlies many tools.
- OpenSCAD with manifold backend — booleans up to 100x faster than the legacy CGAL backend.
Hollowing / drainage / infill prep (resin)
- ★ Lychee Slicer hollowing — see Resin Slicers.
- ChiTuBox Pro hollowing.
- Meshmixer "Hollow" — legacy but excellent.
- UVtools "drainage helper" — adds drain-hole pixels to sliced files.
Pick this if…
- Broken STL, just make it work, on Windows: 3D Builder, or "Fix through Netfabb" inside PrusaSlicer/OrcaSlicer.
- Default FOSS power tool: MeshLab or Blender (3D-Print Toolbox add-on).
- Need to convert STL back to a parametric solid: FreeCAD or CADExchanger.
- Batch / scripted repair pipeline: admesh + trimesh / Open3D.
- Resin hollowing or drain holes: Lychee, ChiTuBox Pro, or Meshmixer (legacy).
- Fast mesh booleans in code: manifold.