OBJ to 3MF

An OBJ is a text file of points and faces with no unit and no print settings. preslice opens one as it is, and Convert to 3MF saves a .3mf that has both.

How do I turn an OBJ into a .3mf?

Drop the .obj on the viewer, or click to browse. It opens in 3D View. Click Convert to 3MF in the file list, and bracket.3mf appears beside bracket.obj and opens. If a bracket.3mf is already in the list, the new one is bracket (2).3mf. The size is in millimetres.

Which parts of an OBJ come across?

The shape and its objects. Each o line in the file becomes one object in the .3mf, with the same name. Quads are split into two triangles each. Colours and textures in the .mtl file are not read, so the .3mf has no colour. Paint it in your slicer.

Why is my model 25.4 times too small?

An OBJ stores bare numbers with no unit, and preslice reads them as millimetres, like every slicer. A part drawn in inches comes out 25.4 times too small. Check the Size row under the mesh in 3D View before you convert: if a part you drew 100 mm wide reads 3.94, scale it by 2540 % in your slicer. See a model opens at the wrong size.

Why is my model lying on its side?

Blender points up along Y by default, and a slicer points up along Z. preslice copies the numbers as they are, and so does PrusaSlicer's OBJ reader, which reads each v line into x, y, z with no axis swap. Rotate the part 90° in the slicer, or change the up axis in the exporter and save again.

Where do the print settings come from?

Nowhere, at first: an OBJ carries none, so the new file is geometry alone. Open Convert, pick a slicer, and the file gets that slicer's default printer, filament and process settings.

Can I edit the OBJ first?

Yes. The Raw tab shows the OBJ as text. Fix a name or an o line there, then convert. See Raw.