Converting 3DM to SolidWorks: Step‑by‑Step WorkflowConverting Rhinoceros (.3dm) files to SolidWorks can be straightforward if you understand the formats, prepare your geometry properly, and follow a systematic workflow. This article walks through the entire process: file preparation in Rhino, selecting the right export/import options, handling NURBS vs. mesh data, repairing geometry, re-creating features where needed, and best practices to avoid common pitfalls.
Why conversion can be tricky
- .3dm (Rhino) stores both precise NURBS surfaces/curves and polygon meshes.
- SolidWorks is a history-based parametric CAD system that prefers watertight, manifold geometry and either native solid bodies (from NURBS) or high-quality meshes for reference.
- Direct feature translation (sketches, parametric features) is rarely preserved automatically — most conversions transfer geometry only, not design intent.
- Units, tolerances, and surface continuity issues can cause failures or poor-quality solids after import.
Short fact: The .3dm file often contains NURBS surfaces; SolidWorks imports these as generic surfaces or solids, not native parametric features.
Overview of the workflow
- Inspect and prepare the Rhino model (units, layers, naked edges).
- Decide target geometry type: solid bodies (preferred) or surfaces/meshes.
- Export from Rhino to a compatible format (native .3dm, IGES, STEP, or Parasolid for NURBS/solid data; STL/OBJ for meshes).
- Import into SolidWorks using appropriate import options.
- Repair geometry and knit surfaces into solids if necessary.
- Rebuild features or create new SolidWorks parametric geometry as needed.
- Validate and finalize the model (check units, mass properties, and manufacturability).
Step 1 — Inspect and prepare in Rhino
- Set the correct units: match SolidWorks units to avoid scale issues.
- Run Analyze > Edge Tools > ShowEdges to find naked edges (open seams). Aim for zero naked edges on parts you want as solids.
- Use Inspect > ShowRemeshed to see mesh density if the model contains meshes.
- Clean up duplicate surfaces, tiny edges, and degenerate faces. Use commands: Purge, Join, MergeAllFaces, and Rebuild if necessary.
- If the model is made of many small surfaces, consider using Rhino’s MatchSrf and Join to improve continuity.
Practical tips:
- If you need a solid in SolidWorks, ensure surfaces are joined and form a closed volume in Rhino.
- If converting complex freeform surfaces, consider simplifying unnecessary detail that will not transfer usefully into a parametric CAD workflow.
Step 2 — Choose the best export format
Options and trade-offs:
- STEP (.step, .stp): Good for transferring solids and NURBS-based geometry. Widely supported. Often the safest for assemblies and multiple bodies.
- IGES (.igs, .iges): Useful for surface data and NURBS but can produce more fragmented surfaces. Use when STEP fails.
- Parasolid (.x_t, .x_b): Native format for Parasolid kernel; excellent for solid data and preserving topology where supported. SolidWorks supports Parasolid well.
- Rhino (.3dm) direct: SolidWorks can open .3dm files (depending on SolidWorks version), but behavior may vary; some versions handle NURBS better than others.
- STL/OBJ: Exports meshes only — use when the target in SolidWorks is for visualization, CFD, or FEA meshes, not parametric modeling.
Short fact: STEP and Parasolid are generally the best choices for transferring solid NURBS geometry into SolidWorks.
Step 3 — Export from Rhino
- For STEP/IGES: File > Export Selected > choose STEP/IGES.
- For Parasolid: File > Export Selected > choose Parasolid (.x_t or .x_b).
- If you keep .3dm: ensure Rhino layers and object types are tidy.
- Export settings:
- For STEP: choose AP214 for color/assembly needs; AP203 for simpler geometry.
- For IGES: preserve tolerance and maximum chord height for curves/surfaces.
- For Parasolid: use default compatibility; binary (.x_b) is smaller, ASCII (.x_t) is more interoperable for troubleshooting.
Recommended export tolerances:
- Match Rhino model tolerance to SolidWorks document tolerance. Typical tolerance: 0.001–0.01 mm for precise parts; 0.01–0.1 mm for visual models.
Step 4 — Import into SolidWorks
- Open SolidWorks, then use File > Open and pick the exported file (.step/.iges/.x_t/.3dm). For assemblies, open as assembly.
- In the Open dialog click Options before opening and set import behavior:
- For STEP/Parasolid: choose “Import as solid body” if possible.
- For IGES: consider “Import as surface bodies” if solids fail.
- For .3dm: SolidWorks’ Rhino import will convert surfaces; use “Try to form solids” if available.
- Check “Heal faces” or “Try to form solid” options when present.
- For mesh formats (STL/OBJ): use File > Open > select file type and then the Import Options to set tessellation quality.
Common import issues:
- Disconnected faces, small gaps, inverted normals, and multiple coincident faces.
Step 5 — Repair and knit geometry in SolidWorks
- Use Import Diagnostics (Tools > Evaluate > Import Diagnostics) to find and fix gaps and bad geometry. Use “Attempt to heal” and manually delete/repair problem faces if automated healing fails.
- For surface bodies: use Insert > Surface > Knit to combine surfaces and check “Try to form solid” to create a solid body.
- Close small gaps with Fill Surface or Boundary Surface. Use Trim and Extend Surface for larger mismatches.
- For assemblies: use Move/Rotate to align parts; use Combine or Boolean operations for multi-body parts where needed.
Example fixes:
- If Knit fails because of tolerance mismatch, reduce model complexity or re-export with tighter tolerance from Rhino.
- Use Split Line or Delete Face + Patch for tricky topology cleanup.
Step 6 — Rebuild parametric features
- Imported solids are dumb geometry (no features). Rebuild critical features:
- Create new sketches on faces to recreate holes, fillets, chamfers, and boss features.
- Use Convert Entities and Intersection Curve to derive geometry from imported surfaces for accurate placement.
- Use FeatureWorks (if available) to recognize features automatically; results vary and often require manual correction.
- For sheet-metal parts imported as solids, use Convert to Sheet Metal or recreate flanges with proper bend allowances.
Practical example:
- For a housing imported as a single solid, create new sketches for mounting bosses and use Extrude/Cut features rather than editing native geometry.
Step 7 — Validate and finalize
- Check units, mass properties, center of mass, and section views to ensure integrity.
- Run interference and draft analysis if part will be manufactured.
- Save a SolidWorks part (.sldprt) or assembly (.sldasm) with a clear naming convention and version notes describing the import source and any repairs done.
Common problems and quick remedies
- Gaps/naked edges after import: Try tighter export tolerance from Rhino, use Import Diagnostics, or manually fill surfaces.
- Too many small trimmed surfaces: Rebuild or simplify surfaces in Rhino before export. Use MergeAllFaces and Rebuild.
- Failure to form solids: Export to Parasolid or STEP instead of IGES; ensure surfaces are watertight.
- Loss of color/metadata: Use STEP AP214 to include colors; some metadata won’t transfer—document it separately.
Best practices summary
- Use STEP or Parasolid for solids; IGES for tricky surfaces; STL only for meshes.
- Match and verify units/tolerances before exporting.
- Clean and join surfaces in Rhino so solids import as solids.
- Use Import Diagnostics and Surface Knit in SolidWorks to repair imported data.
- Recreate parametric features in SolidWorks rather than trying to convert geometry into features automatically.
Useful commands checklist
Rhino:
- Purge, Join, MatchSrf, MergeAllFaces, Rebuild, ShowEdges, Export Selected
SolidWorks:
- File > Open (with Options), Import Diagnostics, Knit Surface, Fill Surface, FeatureWorks, Convert to Sheet Metal, Mass Properties
Converting .3dm to SolidWorks combines careful preparation, the right file format choice, and systematic repair and rebuilding inside SolidWorks. When you follow the steps above and prefer STEP/Parasolid for solids, the process becomes reliable and predictable even for complex freeform geometry.
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