Convert 3DM to OBJ

Many 3D editors, game engines, renderers, and mesh-repair tools require a polygon mesh rather than Rhino's native .3dm format. Converting creates an .obj copy for those applications, but it replaces editable NURBS geometry with tessellated polygons.

What the 3DM format is

.3dm is McNeel Rhino's native format for CAD and 3D modeling. Rhino is used in product design, architecture, jewelry, industrial design, engineering, and fabrication. A 3DM file can contain NURBS curves and surfaces, solids, meshes, layers, blocks, annotations, construction geometry, and appearance data.

NURBS surfaces store mathematically precise curves and surfaces; OBJ does not store that geometry directly. The conversion must therefore create a polygon mesh from each supported surface.

What the OBJ format is

.obj is an open, text-based polygon format supported by Blender, Autodesk 3ds Max, Maya, many renderers, game-engine workflows, mesh-repair applications, and 3D-printing software. An OBJ can store vertices, texture coordinates, vertex normals, polygon faces, and references to a separate .mtl material file.

OBJ is useful for broad compatibility and mesh-based editing or rendering. It does not reliably preserve NURBS surfaces, parametric history, Rhino dimensions, layers, blocks, annotations, or native editing operations. Materials and textures may require the accompanying .mtl file and image files, and support varies between importers.

Convert with Rhino

1. Open the .3dm file in Rhino. Turn off or hide unwanted layers, remove construction geometry, and check that the required objects are valid.
2. Select the objects to convert, then choose File → Export Selected. To export the entire model, use File → Export and follow the exporter options.
3. Choose Wavefront OBJ (*.obj) and specify an output filename.
4. Set the mesh quality in Rhino's OBJ export or mesh options. Use a finer mesh, smaller tolerance, or lower maximum angle for curved, reflective, or highly detailed surfaces. Use a coarser mesh for previews or smaller files.
5. Enable vertex normals and texture coordinates when the destination supports them. Export material references if appearance data is needed.
6. Open the OBJ in the target application and inspect scale, shading, normals, gaps, object groups, and textures. Keep the generated .mtl and image files with the OBJ, using the paths expected by the importer.

Rhino is usually the best desktop option because it reads 3DM natively and gives direct control over tessellation. A current Rhino evaluation or licensed installation can perform the conversion; licensing terms and evaluation limits can change.

Convert without Rhino

For a one-off conversion, online services such as CloudConvert or CAD Exchanger Web may accept .3dm and export .obj. Upload the file, choose OBJ, select mesh quality when available, start the conversion, and download every supplied output file. Confirm the result in a 3D viewer or mesh editor before relying on it.

Online converters can omit unsupported Rhino objects, layers, materials, textures, or construction data, and usually provide less control over tessellation than Rhino. Do not upload confidential or customer-owned CAD files unless the service's current retention and privacy terms are acceptable. CAD Exchanger Desktop is a separate commercial option to check when a local workflow is required and its current 3DM import and OBJ export support meets the project needs.

Quality and compatibility limits

Tessellation controls the result. A coarse mesh makes curved surfaces visibly faceted and can remove small features; a fine mesh increases polygon count, file size, memory use, and import time. Set tolerance according to the model's units and intended use: a tolerance suitable for a small millimeter-scale part may be excessive or unsuitable for a building model.

OBJ has no universally enforced unit declaration. Coordinates are written to the file, but the receiving application may interpret them according to its own scene units. Measure a known dimension after import and rescale the mesh if necessary.

Inspect face orientation and topology after conversion. Reversed normals can produce dark or invisible faces, while gaps, non-manifold edges, and self-intersections can affect rendering and 3D printing. Recalculate or flip normals and run mesh-repair tools when required. A watertight NURBS solid does not guarantee a watertight exported mesh.