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Onshape import mesh: what you can and can't do with an AI 3D model in CAD
Onshape imports STL and OBJ as mesh bodies, not solids. How to use an AI mesh as a reference, and when to convert it or model in CAD instead.
2 min read
Quick answer
Can you edit an STL or OBJ mesh in Onshape?
Not as a solid. Onshape imports STL and OBJ files as mesh bodies, which you can view, position and measure against, but not fillet, shell or extrude like a CAD part. Use an AI mesh as a reference to model around, such as a mount that fits a sculpted figure, or convert it to a solid in another tool first.
Meshes and CAD solids are different things
CAD solids, Onshape's native geometry, are made of exact surfaces: planes, cylinders, splines. You can fillet an edge or shell a body because the software knows the true shape.
Meshes (STL, OBJ, GLB) are thousands of flat triangles approximating a shape. Every AI 3D generator outputs meshes. They are great for organic shapes and terrible for "make this hole exactly 5.2 mm".
When Onshape imports an STL or OBJ, it keeps it as a mesh body. Onshape staff have described these on the Onshape forum as not editable like native parts.
What a mesh body is still useful for
- A reference to model around. Import a sculpted figure and design a stand, a case or a mount that fits it.
- Fit checks in an assembly: does the organic part clash with the mechanical one?
- Measuring overall dimensions and positions.
A typical hybrid workflow
- Generate the organic part, say a character's head for a lamp, in an AI tool, and export OBJ.
- Import it into Onshape and place it.
- Model the mechanical parts in CAD around it: the lamp base, the socket mount, the screw holes.
- Export the CAD parts and the mesh separately, and print or render them together.
If you really need it as a solid
Converting a mesh to a solid works best on simple, low-polygon meshes:
- FreeCAD can turn a mesh into a solid in its Part workbench. Reduce the triangle count first. A dense AI mesh produces an enormous, slow solid.
- Fusion has mesh-to-BRep tools for the same job.
For an organic AI model, the result is a solid made of thousands of tiny flat faces. That's technically editable, but you still can't fillet "the edge of the ear". For anything that has to be precise, model it in CAD from the start. If you're starting from a drawing, see technical drawing to 3D with AI for where AI helps and where it doesn't.
Try it
Generate the organic part in Vi3W, export OBJ, and design the precise parts around it in Onshape.
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