STL CAD Cleaner 1.0.0

Turns triangle-soup STL and CAD meshes into clean, editable n-gon models: merge by distance, flat n-gons from coplanar triangles, sharp edges and smooth shading by angle, origin to the base. Blender 4.2 LTS or newer, tested on 4.2 LTS and 5.2 LTS.

Install

1. Extension zip (recommended): stl_cad_cleaner-1.0.0.zip. Drag it into Blender, or go to Edit > Preferences > Get Extensions, open the drop-down at the top right and choose Install from Disk.
2. Legacy zip: stl_cad_cleaner-1.0.0-legacy.zip. Go to Edit > Preferences > Add-ons > Install from Disk, then tick STL CAD Cleaner.

The panel is in the 3D Viewport sidebar. Press N and open the CAD tab.

Clean a model, step by step

1. Import your model (File > Import > STL) and select it. You can select several objects.
2. Set 1 Blender unit =. STL files are almost always in millimetres, so choose 1 mm. Auto follows Scene > Units.
3. Click Preview Result. The report shows how many faces, n-gons and sharp edges you would get and the volume change. Nothing is changed.
4. Click Clean CAD Mesh. The mesh is welded, flat faces are rebuilt, straight-edge vertices are removed, sharp edges are marked, shading is set to smooth and the origin moves to the base. The report lists the result per object.
5. Check the report: the volume of a closed mesh should read +0.000%. If it warns about a volume change, lower Distance.
6. Edit: select a whole flat face and inset, extrude or bevel it. Ctrl+Z undoes the clean in one step.

Settings

Tips

• Use Preview Result first on a new kind of file: if the face count barely drops, the surface is not really flat (a scan or a sculpt) and this add-on is the wrong tool.
• Noisy export (vertices off by a few thousandths of a millimetre)? Raise Distance to 0.02 and Flatness to 0.05.
• Very fine round parts (thousands of facets): lower Angle to 0.1 and Flatness to 0.001 to keep every facet.
• Keep a copy of the original if you may want it back: Clean CAD Mesh changes the mesh itself.

Limits

• Works on the base mesh; modifiers are not applied. Meshes with shape keys and zero-scale objects are skipped and the report says why.
• A face with a hole cannot exist in Blender, so a plate top with holes becomes several n-gons around the holes.
• Curved surfaces are not turned into one smooth surface: they stay as strips of faces. Facets closer together than Angle may merge, never moving the surface more than Flatness.
• No hole filling, no repair, no remeshing. UV maps and vertex weights are not kept for welded corners (STL files have none).
• Mark sharp edges replaces existing sharp marks. A mesh shared with unselected objects is cleaned for all of them and its origin is left alone.

Troubleshooting

• Nothing changed (the face count stays the same): the units are probably wrong. Set 1 Blender unit = 1 mm.
• Face count only dropped a little: the surface is curved or noisy; see Tips.
• Report says "not watertight": the model has holes. The clean still works; use a repair tool such as Print Fix first if you need a closed mesh.

Uninstall

Edit > Preferences > Get Extensions (or Add-ons), find STL CAD Cleaner and remove it. Your cleaned meshes stay as they are.

Licence

GPL-3.0-or-later. Copyright Sonneblom Digitaal.

Changelog

1.0.0: first release.