Best Practices for Importing 3DM Files into SolidWorksImporting 3DM (Rhino/3D modeling) files into SolidWorks can be straightforward, but achieving clean, editable geometry often requires preparation, the right settings, and post‑import cleanup. This article covers practical workflows, common pitfalls, and techniques to preserve surface integrity and parametric modeling efficiency.
What is a 3DM file?
3DM is the native file format of Rhino (Rhinoceros). It stores NURBS geometry (curves, surfaces), meshes, annotation, layers, and other scene data. Because 3DM commonly uses NURBS, it can carry high‑quality freeform surface data that, when imported properly, integrates well with SolidWorks’ surfacing and solid modeling tools.
Before you export from Rhino (or obtain the 3DM)
Prepare the model at the source whenever possible — this produces the best results in SolidWorks.
- Clean geometry: Remove unused layers, hidden objects, duplicate geometry, small stray curves, and internal faces.
- Check scale and units: Ensure the model units match the intended units in SolidWorks (mm, inches, etc.).
- Simplify where appropriate: Reduce excessive subdivision of surfaces and remove micro‑features that will create import problems.
- Join surfaces where logical: Where surfaces are meant to be continuous, join them into logical polysurfaces to reduce the number of separate bodies in SolidWorks.
- Bake or freeze history: If using parametric Rhino features (Grasshopper), bake to final geometry.
- Save a backup: Keep an original 3DM and an export copy for troubleshooting.
Which import method to choose in SolidWorks
SolidWorks can import 3DM files directly using File > Open (select 3DM), or you can export from Rhino to an alternative format that SolidWorks sometimes handles better (IGES/STEP). Choose based on desired outcome:
- Direct 3DM import: Maintains NURBS surfaces where supported. Good first attempt.
- STEP (.step/.stp): Best for transferring solid topology and assembly structure when available.
- IGES (.igs/.iges): Useful for surfaces but can create many trimmed surfaces; use if STEP/3DM fail.
- Parasolid (.x_t/.x_b): Best for native SolidWorks solids — requires export from a tool that supports Parasolid.
If you can control the source export, try STEP or Parasolid for parametric solid transfer. Use 3DM when preserving Rhino NURBS is important or when the model relies heavily on freeform surfaces.
SolidWorks import options and settings
When opening a 3DM (or other CAD) file in SolidWorks, the Import Options dialog is crucial.
- Import as Solid Body vs. Surface Body: If geometry is watertight, import as Solid to get solids and features. If not watertight, import as Surface for manual stitch/repair.
- Heal/Repair Options: Enable “Try to form solid” or “Perform full entity translation” where available to let SolidWorks attempt automatic fixes.
- Link to external references: Avoid linking unless you require associative updates from the original file—links can complicate file management.
- Import diagnostics: After import, run Import Diagnostics (Tools > Evaluate > Import Diagnostics) to find and fix gaps, bad faces, and invalid topology.
- Tessellation settings: For visualization exports (like STL previews) control deviation and chord tolerance to balance fidelity and file size.
Common problems and how to fix them
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Non‑watertight geometry (gaps/holes)
- Use Import Diagnostics to find and heal gaps.
- Use Surface > Knit to stitch surfaces, then try to form a solid.
- In Rhino, look for naked edges and rebuild or extend surfaces before export.
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Many tiny faces / fragmented topology
- In Rhino, merge faces and simplify surfaces (Rebuild, MergeSrf).
- In SolidWorks, use Knit Surface and Delete Face (Delete and Patch) to simplify.
-
Unexpectedly imported meshes instead of NURBS
- Ensure Rhino exports NURBS and not triangulated meshes.
- If only meshes are available, use ScanTo3D or third‑party tools to convert mesh to surfaces/solids.
-
Unit/scale mismatches
- Verify units in Rhino before export. In SolidWorks, use Options > Document Properties > Units or set units at import.
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Non‑manifold or self‑intersecting geometry
- Fix in Rhino: boolean cleanups, remove duplicates, check normals.
- In SolidWorks, use advanced repair tools (Delete Face, Knit, Move Face).
Workflow examples
Example A — Targeting parametric solids in SolidWorks
- In Rhino: Merge surfaces into closed polysurfaces where possible. Export as STEP/Parasolid if available.
- In SolidWorks: File > Open > select STEP/Parasolid; in Import Options choose “Import as solid body.”
- Run Import Diagnostics, heal gaps, and feature‑recognize where feasible (FeatureWorks can help).
Example B — Working with complex freeform surfaces
- In Rhino: Keep high‑quality NURBS surfaces; remove tiny features; ensure correct normals.
- Export 3DM.
- In SolidWorks: Open 3DM as Surface Bodies, use Surface tools (Loft, Boundary, Knit) to reconstruct or stitch and then form solids.
Tips for large or complex models
- Break the model into smaller parts before import to reduce memory use and simplify repairs.
- Import only necessary components—use layers to export subsets.
- Use lightweight preview or graphics settings in SolidWorks if display becomes slow.
- Consider third‑party translators (e.g., Rhino3D Importer plugins, Datakit) when native import fails.
Post‑import cleanup and best practices inside SolidWorks
- Run Import Diagnostics immediately then use Repair Tools.
- Use FeatureWorks or “Recognize Features” to convert geometry into parametric features where possible.
- Replace problematic imported geometry with native SolidWorks features (extrudes, revolves) to regain parametric control.
- Create configurations or derived parts for variants rather than reimporting.
- Maintain a clear naming/layering convention to keep imported geometry organized.
Automation and scripting
- Rhino: Use scripts or Grasshopper to automate cleanup and export batches.
- SolidWorks: Use macros or the API to automate import settings, run Import Diagnostics, and perform repetitive fixes.
- Consider custom pipelines for frequent transfers (e.g., a script that exports STEP with specific tolerance, then a SolidWorks macro that opens, heals, and saves).
When to consider remodelling instead of importing
If the imported geometry is too messy, or you need full parametric control, remodelling parts in SolidWorks can be faster long‑term. Indicators for remodelling:
- Highly fragmented topology with thousands of tiny faces.
- Imported surfaces that prevent creating required features (fillets, shells).
- Critical manufacturing features that must be parametric.
Summary checklist
- Verify units and scale in source file.
- Clean and simplify geometry in Rhino before export.
- Prefer STEP/Parasolid for solids; use 3DM for NURBS surfaces.
- Use proper import options in SolidWorks and run Import Diagnostics.
- Stitch/knit surfaces, fix naked edges, and rebuild topology as needed.
- Consider remodelling if import repair is more work than creating native geometry.
If you want, I can: provide a Rhino checklist script to prepare files, write a SolidWorks macro to automate import diagnostics, or review a specific 3DM and suggest fixes. Which would you like?
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