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Repair a .3mf with mesh errors

Bambu Studio marks the object with Error: %1$d non-manifold edges, %2$d non-manifold vertices (GUI_ObjectList.cpp), or Cura opens a Model Errors warning. The mesh has edges that do not join into a closed surface. preslice shows you where they are, and fixes one kind.

Can I print it anyway?

Often, yes. A slicer closes small gaps itself, and a stray triangle may never show in the print. Slice it and read the layer preview before you repair anything. Bambu Studio refuses some operations with "%s" part's mesh contains errors. Please repair it first. (GUI_ObjectList.cpp).

What is a non-manifold edge?

An edge where more than two triangles meet, like a fin stuck on a cube. An edge with only one triangle is a hole. A solid needs every edge shared by exactly two, so the slicer can tell inside from outside.

What does Cura's Model Errors mean?

The highlighted areas indicate either missing or extraneous surfaces. Fix your model and open it again into Cura. (SolidView.py). Cura paints the open spots red in the X-ray view. It is the same problem with a different name.

How do I find the bad edges with preslice?

  1. Drop the .3mf on preslice.co.
  2. Open the 3MF Content tab and expand Mesh objects.
  3. Each mesh has a Status row. Click non-manifold to zoom the 3D view to the bad edges.

Red lines are edges shared by more than two triangles. Amber lines and dots are holes.

What does Weld mesh fix?

A mesh saved with every corner repeated per triangle looks open to a slicer even though the surface is closed. Weld mesh merges those duplicate vertices. It only shows next to a mesh that welding closes completely:

  1. Click Weld mesh next to the non-manifold status.
  2. Click the tab with your file name, then the button that starts with Download 3MF.

The weld is a change you can undo. preslice fills no holes, flips no faces and removes no extra triangles. A mesh without the button needs a repair tool.

Which tools fill holes?

Tool Where
Bambu Studio Right-click the object, Fix model. Windows 10 and later only (GUI_Factories.cpp)
PrusaSlicer Right-click, Fix by Windows repair algorithm. Windows only
Blender The 3D Print Toolbox add-on checks and cleans a mesh on any system
Meshmixer Analysis, Inspector. No longer developed, but still runs

Repair the shape in one of these, export it, and open the result in preslice to check the status reads manifold.

What if the archive itself is damaged?

That is a different problem. If preslice says Geometry missing and names a part, the part is gone from the file and no repair tool can bring it back. See the file does not contain any geometry data. If the file will not open at all, download it again.