Model repair: how holes and mesh errors are dealt with

Why a model needs repairing

A model without holes and without self-intersection prints without problems. Such models are called manifold. Many downloaded, scanned or sculpted models do have errors though, even if they look fine in a viewer.

Errors appear during export, when bodies are merged, during scanning or when converting between formats.

What we repair

After you upload, the slicer on our server prepares the model for printing. Small holes in the mesh are repaired automatically in the process. If the error is bigger, for example a whole face is missing or the model was merged badly, we will write to you.

The repair is done by an automatic tool that closes smaller holes. It does not change the shape of the model and cannot guess what you meant. So it is not a substitute for a clean model.

How to repair it yourself

• Slicer on opening. Several slicers, such as PrusaSlicer, repair small errors automatically when they load a file.
• Blender. An add-on for checking models for 3D printing shows holes and non-manifold edges, see Blender.
• Windows 3D Builder. Offers to repair a file when you open it.
• The original CAD. It is best to fix the error where it arose and export again.

How to prevent errors

Export a single closed solid from CAD to 3MF or STL, not several overlapping ones. When merging bodies, use a boolean union, do not just push them into each other.

If you downloaded a model, open it in a slicer. It often reveals an error that you cannot see in a viewer.