Intermediate step to convert STL mesh to shape?

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joey_dBol
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Joined: Sun Nov 28, 2021 10:12 pm

Intermediate step to convert STL mesh to shape?

Post by joey_dBol »

Hello,

I have several relief carvings that are in stl format. Following the usual steps to go from the mesh to a solid that freecad can process for tool paths fails every time. I've used several tools (including freecad) to analyze and repair the mesh, which all seem to complete successfully, but freecad still hangs at 99% while sewing the faces. I let it run for over a day but still sits at 99%. I recently discovered meshmixer which had no problem creating a solid from the mesh, however my problem now is finding the correct format to export the geometry such that freecad can import it and make tool paths. The available formats to export from meshmixer are: .3mf, .amf, .dae, .ply, .smesh, and .wrl (ignoring the stl variants, and obj). Any idea which one would work with freecad? By trial and error I've tried .wrl, and .dae with no luck. Any advice is welcomed. Thanks in advance.
TheMarkster
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Re: Intermediate step to convert STL mesh to shape?

Post by TheMarkster »

Attach one of the files if you can.
wmayer
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Re: Intermediate step to convert STL mesh to shape?

Post by wmayer »

I've used several tools (including freecad) to analyze and repair the mesh, which all seem to complete successfully, but freecad still hangs at 99% while sewing the faces. I let it run for over a day but still sits at 99%.
The step to create a shape from a mesh takes a lot of time and memory if the number of triangles is too high (depends on your hardware). In v0.20 the algorithm has been optimized a lot so that it should be accomplished much earlier by using less memory.

However, with this function you don't get a proper CAD model. All what you have is a 1:1 conversion of a triangle into a surface. If you e.g. have a set of triangles to describe a cylinder you won't get a single surface but still the same number of surfaces as triangles.
I recently discovered meshmixer which had no problem creating a solid from the mesh
The term solid has nothing to do with the data structure to describe a geometry. Solid only means that your model is watertight.

The point of the function to create a shape from a mesh is that you get a B-REP model so that the CAD kernel can work with it.
domad
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Re: Intermediate step to convert STL mesh to shape?

Post by domad »

Greetings to the Community!
The clarification of @wmayer (!) Is very thorough and professional.
However it would be appropriate to do what @TheMarkster recommended, if the file is over 1 Mb use a cloud service (remember to make the download free / open) and post the link.
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joey_dBol
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Re: Intermediate step to convert STL mesh to shape?

Post by joey_dBol »

Thank you all for the fast responses. I apologize for the delay in responding, I didn't set up notifications and didn't realize my post was accepted and ppl were responding. This is the preprocessed (decimation, analyze/repair, remeshed) version that I try to create the shape from.

https://drive.google.com/file/d/1g2sk__ ... sp=sharing
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joey_dBol
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Re: Intermediate step to convert STL mesh to shape?

Post by joey_dBol »

I'm not sure what I did differently this time around, but I ran the same procedure and it completed mesh->shape successfully in ~5hrs. It may, or may not be related, but I did update gmsh this morning before trying again. In any case, thank you so much for the responses.
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