A Rhino model is usually a .3dm file. CADProps does not open 3DM. Renaming it to STEP, IGES or STL does not convert the Rhino document, and it can hide the fact that you still have the native file.
To inspect the shape without Rhino, ask for an export that matches the next task. Rhino documents often contain NURBS surfaces, open polysurfaces and meshes in the same file. The export format decides which of those you receive.
Pick the export from the job
| Next task | Ask for | Limit to expect |
|---|---|---|
| CAD or CAM that wants precise geometry | STEP, if the Rhino model is a closed solid or a polysurface the exporter can translate | Feature history is not a Rhino object list |
| A surface workflow that already uses IGES | IGES | Area can exist when a closed-solid volume does not |
| Printing or a mesh-only viewer | STL, with the unit and mesh tolerance written down | STL does not declare a reliable physical unit |
| Keep editing the Rhino model | The original 3DM, in Rhino or another 3DM reader | This site is not that reader |
Open STEP in the STEP viewer, IGES in the IGES viewer and STL in the STL viewer. STEP vs IGES and STEP vs STL explain why those files are not substitutes for each other.
Units and closure fail in different ways
Rhino models are often modelled in millimetres, but the file you receive may not say so in a way the next program trusts. Check one known dimension after import. A 25.4 ratio is the usual inch/millimetre warning. Do not scale by eye until the view looks familiar.
A closed polysurface can support a solid volume. An open set of surfaces can still have area and a perfectly convincing shaded picture. Do not record that volume as zero. Record it as unavailable until the sender exports a closed solid or you accept that the task only needs surfaces.
STL is a triangle mesh. CADProps assumes millimetres for STL and OBJ coordinates because the mesh does not reliably declare a unit. Mesh dimensions, area and volume are approximate, and volume requires a closed, consistent mesh. Do STL files have units? is the scale check. A finer mesh is still not the original NURBS surface.
What the export will not keep
Rhino layers, object names, render materials and construction history are not a promise of any neutral export. A STEP or IGES file can carry geometry and still drop the layer structure you use to find parts. An STL drops the NURBS surfaces entirely.
If the Rhino file is a set of loose surfaces rather than one solid, say that in the request. An exporter that joins them automatically may close gaps the designer left open.
A practical handoff
- Leave the 3DM unchanged.
- Ask for one export format, the model units and whether the body is supposed to be closed.
- Open that export in the matching viewer above.
- Measure one known length.
- Use volume or mass only after closure and units are confirmed. Mass needs a density you choose.
- If the export is wrong, ask for a new export from Rhino. Do not repair a mesh and call it the Rhino master.
This is a way to review an agreed derivative. It is not a Rhino license and not a 3DM converter.
Original article: CADProps · https://www.cadprops.com/guides/open-3dm-without-rhino/