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To preserve CAD and 3D model files, keep the native file as your master and export a neutral, standards-based derivative for long-term access — STEP (ISO 10303) for mechanical CAD, IFC for BIM, and glTF or OBJ plus the raw scan for mesh and point-cloud data. Then document the software, units, scale and export settings, and fixity-check every file. CAD preservation is harder than image preservation because neutral formats deliberately drop the parametric intelligence that makes a model editable, so a two-copy strategy is essential.
Why is CAD harder to preserve than images?
A CAD file is not a picture; it is a parametric program. A SolidWorks part stores a feature tree — extrude, fillet, pattern — that regenerates the geometry. Neutral archival formats like STEP capture only the result (the final boundary representation), not the recipe. So unlike a TIFF, you cannot fully preserve a CAD model in a single open format without losing design intent. That trade-off shapes the entire strategy.
Which formats should I use?
Match the format to the kind of model:
| Model type | Native master examples | Neutral archival format |
|---|---|---|
| Mechanical CAD | .sldprt, .dwg, .catpart | STEP AP242 (.stp) |
| Building / BIM | .rvt, .pln | IFC (.ifc) |
| Mesh / surface | .max, .blend | OBJ (+ MTL), PLY, glTF/GLB |
| 3D scan / point cloud | scanner-native | E57 (master), glTF (access) |
STEP AP242 is preferred over the older AP203 because it retains assemblies, colours and basic product-manufacturing information.
Step by step: preserving a mechanical CAD model
- Keep the native file (
pump_housing.sldprt) read-only as the master. - Export to STEP AP242 from the native application. In SolidWorks:
File → Save As → STEP AP242, with units and coordinate system confirmed. - Export a lightweight access copy in glTF/GLB so the model can be viewed in a browser without CAD software.
- Record metadata (see below).
- Checksum every file with SHA-256.
- Bag it with BagIt for transfer to your repository.
For mesh data you can convert and inspect with open tools:
bash
# convert an OBJ master to a compressed glTF access copy
obj2gltf -i pump_housing.obj -o pump_housing.glb --draco
# verify a STEP file opens and report its bounding box / units
# (FreeCAD headless)
freecadcmd -c "import Part; s=Part.Shape(); s.read('pump_housing.stp'); print(s.BoundBox)"What metadata must I capture?
CAD geometry is meaningless without context. At minimum, record:
- Originating software and exact version (geometry kernels change between releases).
- Units and scale — a model in millimetres versus inches is a silent disaster.
- Coordinate system and any datum.
- The export settings used to make the neutral copy.
- Linked drawings, BOMs or specifications.
Store this in a sidecar file next to the model, plus a checksum for each file.
Why did my STEP export lose the feature tree?
Because it is supposed to. STEP records the final solid, not the parametric history, constraints or sketches. If you reopen a STEP file you get a "dumb solid" you cannot easily re-edit. This is not a bug — it is the cost of software independence. The native master is what preserves editability, which is exactly why you keep both copies.
How do I preserve 3D scans and point clouds?
Treat the raw scanner output as the master and never re-process over it. Export E57 as a neutral point-cloud archival format, and produce a decimated glTF/GLB mesh for access and the web. Note the scanner model, resolution, registration method and georeferencing if the scan is tied to real-world coordinates — those details determine whether the data is reusable for measurement later.
What pitfalls trip people up?
- Assuming STEP is enough — it drops design intent; keep the native file.
- Forgetting units — the most common cause of unusable archived models.
- Embedding proprietary fonts/materials that don't survive conversion.
- Skipping a visual check — always render the derivative and compare to the original.
Key Takeaways
- Keep the native CAD file as the master; add a neutral derivative for access.
- Use STEP AP242 for mechanical CAD, IFC for BIM, OBJ/PLY/glTF for meshes, E57 for point clouds.
- Neutral formats drop parametric history — that loss is expected, not a failure.
- Always record software version, units, scale and coordinate system.
- Produce a glTF/GLB access copy so models view without CAD software.
- Checksum every file and visually verify the derivative before trusting it.
Frequently Asked Questions
What is the best archival format for CAD files?
For mechanical CAD, STEP (ISO 10303, .stp) is the leading neutral archival format because it is an ISO standard, vendor-neutral and preserves precise B-rep geometry. IFC is the equivalent for building/BIM models.
What format should I use for 3D scanned or mesh models?
For mesh and point-cloud data, use open formats such as PLY, OBJ with MTL, glTF/GLB for visualisation, and E57 for point clouds. Keep the raw scan data as the master and a glTF derivative for access.
Should I keep the native CAD file as well as a neutral copy?
Yes. Retain the native file (e.g. .dwg, .sldprt) as the master because it holds parametric history and features, and add a neutral STEP/IFC derivative for software-independent long-term access.
Why do my converted CAD models lose features or detail?
Neutral formats like STEP store final geometry but drop parametric feature history, constraints and assembly intelligence. That loss is expected; keep the native file to preserve the editable design intent.
How do I document a CAD or 3D model for preservation?
Record the originating software and version, units, coordinate system, scale, the export settings used, and any associated drawings or specifications, alongside a checksum of each file.
Does STEP preserve colours, materials and assemblies?
STEP AP242 supports assemblies, colours and basic product manufacturing information; older AP203 is geometry-focused. Choose AP242 when you need to retain assembly structure and visual attributes.