Free online 3DM to STL converter

A 3D printer or slicer may require STL instead of Rhino’s native 3DM format. Converting also provides a mesh-based file that is easier to share with systems that do not support editable CAD geometry.

What the 3DM format is

3DM is the native file format of Rhinoceros (Rhino), developed by McNeel and supported through the OpenNURBS geometry model. It can store NURBS curves and surfaces, solids, polygon meshes, layers, blocks, annotations, materials, and object attributes. Architects, industrial designers, engineers, and other CAD users use 3DM files for editable modeling work.

A 3DM file can preserve parametric and high-precision surface information, but most printers and slicers cannot process NURBS geometry directly. The model must be tessellated into triangular facets before those applications can use it.

What the STL format is

STL represents a three-dimensional surface as a collection of triangular facets. It is supported by most 3D-printing applications, slicers, rapid-prototyping systems, and mesh utilities.

STL is widely compatible, but it does not preserve NURBS surfaces, modeling history, layers, curves, object names, colors, materials, or most other 3DM metadata. It contains an approximation of the surface, not the original editable CAD model. Binary STL files are normally smaller than ASCII STL files; use ASCII only when a specific application requires it.

How to convert 3DM to STL

Using Rhino

1. Open the .3dm file in Rhino.
2. Check the model units through File → Properties → Units. STL does not reliably carry unit information, so the receiving software must interpret the exported coordinates correctly.
3. Select the objects to export. Select all required objects with Ctrl+A, or leave the selection empty if you intend to export the entire model.
4. Choose File → Export Selected and select STL (*.stl). If no objects are selected, use File → Export and choose STL.
5. Choose binary STL unless the target application specifically needs ASCII STL.
6. Set the mesh options. Use a finer mesh, tighter distance tolerance, and suitable angle tolerance for curved or highly detailed surfaces. Avoid unnecessarily fine settings that create large files without improving the printable result.
7. Save the file, then open it in the target slicer or mesh utility. Check its dimensions, orientation, surface quality, and printability before manufacturing.

Using 101convert.com

For a straightforward conversion without installed software, upload the .3dm file to 101convert.com, choose STL as the output format, start the conversion, and download the result for free. This option provides less control than Rhino over object selection, tessellation, units, and mesh repair; use Rhino when those settings affect the final part.

Quality and compatibility checks

• Mesh accuracy: A coarse tessellation produces visible faceting and can alter curved dimensions. An excessively fine tessellation increases file size and processing time without necessarily improving printer accuracy.
• Watertight geometry: For solid printing, inspect the STL for open edges, holes, duplicate faces, self-intersections, and inconsistent face normals. Invalid geometry can cause missing regions, incorrect walls, or faulty infill in a slicer.
• Units and scale: Confirm the units in Rhino and in the receiving application. A model exported in millimeters can appear 25.4 times too large or too small if the destination interprets the coordinates as inches.
• Model scope: Export only the intended objects. Construction geometry, hidden parts, separate bodies, or overlapping objects can produce an STL that does not match the desired physical part.
• Data loss: After conversion, edits to NURBS surfaces, layers, materials, colors, and modeling history are unavailable in the STL. Keep the original 3DM file as the editable master.