Free online 3DM to FCSTD converter

What the 3DM format is

3DM is the native Rhinoceros 3D file format, based on McNeel’s openNURBS technology. Rhino creates 3DM files for NURBS curves, surfaces, solids, meshes, layers, blocks, materials, annotations, and other modeling data.

You commonly encounter 3DM files when receiving industrial-design, architectural, jewelry, or product models from Rhino, Grasshopper workflows, or applications that support Rhino’s geometry library. A 3DM file can contain editable Rhino objects and scene organization that are not directly represented in a FreeCAD document.

What the FCSTD format is

FCStd is FreeCAD’s native document format. It stores a FreeCAD document, including its object tree, properties, sketches, Part or Part Design features, constraints, and imported geometry.

FCStd is appropriate when the model must be opened and edited in FreeCAD. Saving imported geometry as FCStd preserves the resulting FreeCAD objects, but it normally does not recreate the original Rhino feature history, Grasshopper definitions, layer structure, or parametric relationships.

How to convert 3DM to FCSTD

Recommended workflow through STEP

STEP is generally the most dependable intermediate format for transferring Rhino solids and analytic or NURBS surfaces to FreeCAD.

1. Open the .3dm file in Rhino.
2. Select the objects to transfer. Hide construction geometry, annotations, meshes, and unwanted layers if they are not needed.
3. Use File → Export Selected and choose STEP (*.stp; *.step).
4. In Rhino’s STEP options, use AP214 or AP242 when available, retain solids as solids, and check the unit setting against the original model.
5. Open FreeCAD and select File → Open, then choose the exported .step file.
6. Inspect the imported objects in the 3D view and tree. If required, use the Part workbench’s geometry-checking or refinement tools.
7. Save the document with File → Save As and choose FCStd (*.FCStd).

The resulting file is a FreeCAD document containing imported B-Rep shapes. It can be measured, positioned, combined, cut, and used as the basis for further FreeCAD operations.

Direct import in FreeCAD

Some FreeCAD builds include a 3DM importer, while others do not. Try File → Open with the original .3dm file. If FreeCAD reports an unsupported format or imports incomplete geometry, use Rhino to export STEP instead; importer availability depends on the FreeCAD version and how it was built.

Convert online

You can convert the file on 101convert.com for free without installing software: select the 3DM input, choose FCStd as the output format, upload the file, run the conversion, and download the resulting document. Open the downloaded .FCStd file in FreeCAD and verify the geometry before using it for manufacturing or detailed editing.

Quality, compatibility, and limitations

• STEP normally transfers Rhino solids and surfaces more reliably than direct 3DM import, but it does not transfer Rhino’s modeling history or Grasshopper logic.
• Rhino meshes exported through a mesh format such as STL or OBJ remain mesh data in FreeCAD; they do not become precise editable solids automatically. Use STEP for CAD solids whenever possible.
• Layers, blocks, text, dimensions, materials, render settings, and object-specific metadata may be lost or only partially mapped. Rebuild these elements in FreeCAD when required.
• Check the model units after import. A unit mismatch can make a correctly shaped model appear at the wrong scale.
• Run a geometry check on critical parts. Small gaps, self-intersections, trimmed-surface problems, and unsupported Rhino objects can produce missing faces or invalid solids.
• FreeCAD’s saved document contains the imported result, not a reversible record of the original 3DM conversion. Keep the original 3DM and intermediate STEP files with the FCStd archive.