3MF to STEP

preslice saves a .3mf as STL or OBJ, not STEP. A .3mf holds triangles (3MF Core Specification), and STEP holds exact surfaces, so a CAD tool has to rebuild the solid.

Can preslice convert a .3mf to STEP?

No. Save the mesh as STL or OBJ in preslice, or open the .3mf directly in one of the tools below.

How do I convert a .3mf to STEP in Fusion?

1. Insert, Insert Mesh, and pick the .3mf. It arrives as a mesh body.
2. Right-click the mesh body, Mesh to BRep.
3. File, Export, and pick STEP.

Mesh to BRep turns each triangle into a flat face, so a curved part becomes thousands of facets. The free personal licence limits some mesh tools, so check yours before you start.

How do I convert a .3mf to STEP in FreeCAD?

1. File, Import, and pick the .3mf. FreeCAD reads it as a mesh.
2. Switch to the Part workbench and use Part, Create shape from mesh.
3. Use Part, Convert to solid on the new shape.
4. Select the solid, then File, Export, and pick STEP.

The result has the same facets as the mesh, and a large mesh takes a while.

What does the copy lose?

Every print setting, the plate, and the slicer's paint. STEP keeps the shape. To keep the settings, keep the .3mf as well.

Can I get a smooth STEP back?

Not from a mesh. The curves were cut into triangles when the .3mf was made. Ask the designer for the original STEP, or redraw the part in CAD using the mesh as a reference.