ImportExport 3DM

FreeCAD Import/Export module for Rhino .3dm files. Geometry is read and written as true NURBS — control points, weights, degree, and knot vectors are preserved exactly, with no tessellation.

FreeCAD 1.1+ and rhino3dm ≥ 8.0.0 required.

Supported geometry

Import

rhino3dm type	FreeCAD result
Brep (multi-face solid)	Part::Feature via OCCT
NurbsSurface	Part::Feature with BSplineSurface shell
NurbsCurve	Part::Feature with BSplineCurve wire
SubD	Diagnostic only — NURBS not preserved by originating app
Mesh	Diagnostic only — NURBS not preserved by originating app

Export

FreeCAD surface type	3DM output
BSplineSurface	NURBS surface (control points, knots, weights copied exactly)
Plane	NURBS surface via OCC toNurbs()
Cylinder	Native r3.Cylinder primitive (or NURBS fallback)
Cone	Native r3.Cone primitive (or NURBS fallback)
Sphere	Native r3.Sphere primitive (or NURBS fallback)
Torus	Native r3.Torus primitive (or NURBS fallback)
Other analytic surfaces	NURBS via OCC toNurbs() / toBSpline()

The native-primitives behaviour is controlled by a Preferences option (see below).

Export preferences

Open Edit → Preferences → Import-Export → ImportExport 3DM:

Option	Default	Effect
Export Cylinder / Cone / Sphere / Torus as native primitives	On	Writes analytic surfaces as exact rhino3dm primitives — preserves the analytic shape and produces smaller files. When off, OCC converts them to NURBS approximations.

Requirements

rhino3dm ≥ 8.0.0 must be installed into FreeCAD's own Python interpreter.

FreeCAD 1.1 on macOS

/Applications/FreeCAD_1.1.app/Contents/Resources/bin/python \
  -m pip install "rhino3dm>=8.0.0"

Other platforms

Find FreeCAD's Python interpreter via the FreeCAD Python console:

import sys; print(sys.executable)

Then install:

/path/to/freecad/python -m pip install "rhino3dm>=8.0.0"

Installation

Manual install (macOS / Linux)

cd ~/Library/Application\ Support/FreeCAD/Mod   # macOS
# or
cd ~/.local/share/FreeCAD/Mod                    # Linux

git clone https://github.com/KeithSloan/ImportExport_3DM.git

Restart FreeCAD. The importers and exporter appear automatically in File → Open / File → Import / File → Export.

From the FreeCAD Addon Manager

Not yet listed — install manually for now.

Usage

• Import: File → Open or File → Import — select a .3dm file and choose 3DM from the format dropdown.
• Export: File → Export — choose 3DM.

Report View diagnostics

Version and progress information is printed to the FreeCAD Report View during import and export. The module version and rhino3dm version are printed at module load time.

Blender NURBS pipeline

A companion Blender extension exports NURBS geometry directly to .3dm:

Blender_Export_3DM

This enables a lossless Blender → 3DM → FreeCAD NURBS pipeline:

Blender NURBS surface / Surface Psycho patch
    ↓  Blender_Export_3DM
.3dm file
    ↓  ImportExport_3DM (File → Open)
FreeCAD Part::Feature (exact BSplineSurface)
    ↓  KS_CurvesWB Import commands (optional)
Editable NurbsSurfaceFP / NurbsCurveFP objects

Sample Rhino files

Test .3dm files are in testCases/. Additional Rhino sample files: https://www.rhino3d.com/download/opennurbs/6/opennurbs6samples

Rhino API reference: https://developer.rhino3d.com/api/rhinocommon/

Acknowledgements

• Test cases kindly supplied by Jonne Neva (cheezebreeze), EdWilliams, Sven

Developers

• Keith Sloan
• Chris Grellier

License

GNU Lesser General Public License v2.1 — see LICENSE.