Convert 3DM to STL
Rhino to STL for 3D printing, converted in your browser and written in millimetres by default — the unit every slicer assumes.
What breaks when you convert Rhino 3DM to STL
The scale trap that ruins prints
STL declares no units, and every slicer on the market assumes the numbers are millimetres. A Rhino file authored in metres therefore arrives one thousand times too small: a 1.8 m sculpture turns up as a 1.8 mm speck. We default this conversion to millimetre output for exactly that reason, and the report states the final dimensions so you can check them before you slice.
Open or non-manifold Breps make an unprintable STL
A slicer needs a closed, watertight solid. Rhino will happily model surfaces that do not enclose a volume, and converting those produces an STL with holes that Cura or PrusaSlicer will reject or silently repair into something you did not intend. Run the SelOpenPolysrf and Check commands in Rhino first; fixing it there is far easier than diagnosing it in the slicer.
Render mesh density is your print resolution
The saved mesh is what gets printed, so a coarse display mesh becomes visible faceting on a curved surface — most obvious on cylinders and fillets, which come out as flats. For anything with curvature, raise the mesh settings in Rhino before converting rather than trying to smooth the result later.
Everything except geometry is discarded
STL stores triangles and nothing else: no materials, no colours, no textures, no layers, no object names. This is the format working as designed rather than a failure of the conversion, but it does mean a multi-coloured Rhino model arrives as a single anonymous shell.
Questions
- What units should I choose?
- Millimetres, unless you have a specific reason not to. Slicers assume millimetres, so that is the setting that makes a 100 mm object print at 100 mm.
- Is the output binary or ASCII STL?
- Binary. It is a fraction of the size of ASCII for identical geometry, and every slicer reads it.
- How do I know the model is watertight?
- This converter does not check, because a browser cannot repair the model for you either. Use Rhino’s Check and SelOpenPolysrf commands on the original before converting.
- Will colours from my Rhino model survive?
- No. STL has no way to store colour. If you need colour for printing, convert to GLB or OBJ instead and check that your printer’s workflow accepts it.