Strange problem with Closed Brep export as STL

Grasshopper
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I’m helping a new GH user learn how to use GH for 3D printing, and this is his first real project.

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This is a Closed Brep that, when exported as an STL file for 3D printing, loads up in the slicer with 8 non-manifold edges. When the slicer repairs this the result is quite strange:

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I’ve tried all sorts of things to fix this, but nothing works. After baking the Closed Brep Rhino’s Surface Tools/Show Edges/Naked Edges tool shows nothing. Neither does the Show Manifold Edges.

I’ve made quite a few things thatused individual pieces joined together with SUnion and never had a problem with exported STL files, but there’s something quirky about this one. I just can’t figure out what it is, so I’m hoping someone here will see something I’m missing.

piTFT v2-bb1.gh (33.1 KB)

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I think the offset curve or its input is the issue. Ideally, you’d want the main shape to be deconstructable into flat surfaces and fillets. Or you need to tweak the mesh settings.

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piTFT v2-bb1_meshbrep.gh (31.9 KB)

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Thanks Martin - I thought the problem might be with the meshing of the GH definition. But I had no idea what to do about this. For me meshes have always seemed like a bit of black magic.

I didn’t mention that when the GH Closed Brep is baked and then exported from Rhino as a 3MF file the problem doesn’t happen. Of course I have no idea why this is, but I’m beginning to think that the methodology (code) used to generate STL files is so old (obsolete?) that it should no longer be used with any current CAD/CAM software. I’ve stuck with the STL format simply because “it’s what I’ve always used”; consequently I’ve never really thought about updating to newer technology. I guess we all need to try harder to update our thinking along with the tech we use.

I appreciate the time you took to re-do the GH definition. Your method is what I’d call very non-intuitive - but that’s coming from someone who started with GH more than 6 years ago and is totally self taught. I just think about the geometry - and not the code behind it - and as a result it’s not unusual for me to fall into this type of rabbit hole.

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Glad I was able to help.

With 3MF, it’s likely just different meshing settings. I find it challenging to decide what is ‘right’…