Converting a 3D scan into solid object

[Peter_Schmidt]

Hi everyone,

my goal is to make a hand orthosis of a 3D scanned hand. This orthosis should then be used for finite element analysis. So I imported the 3d scan (stl file) into rhino. First I used the command quadRemesh to get a better mesh. After that I used OffsetMesh to add a wall thickness of 3mm.
This works fine so far. My next step was to use meshToNurb and export it as .step file which is needed for the finite element analysis software. And now the problem begins. When I import the .step file into Fusion360 and cut it in half my orthosis is completely filled with material like in the picture below:

Fusion360 recognises two bodies, but both are filled. And it is also not possible to subtract the inner part from the outer part. Is there anything I am doing wrong in Rhino? I would be very grateful if you could help me to solve my problem!

[davidcockey]

No guarantees but try this:
After converting to polysurfaces using MeshToNURB:
NonmanifoldMerge
CreateRegions
Then export.

Unless NonmanifoldMerge and CreateRegions is used Rhino considers one surface inside another as two separate objects.

I don’t know what happens when the merged object is exported as .step file, nor how Fusion will treat it.

[lander (CAD CAM CNC)]

@Peter_Schmidt

then be used for finite element analysis. So I imported the 3d scan (stl file) into rhino. First I used the command quadRemesh to get a better mesh. After that I used OffsetMesh to add a wall thickness of 3mm.
This works fine so far. My next step was to use meshToNurb and export it as .step file which is needed for the finite element analysis software. And now the problem begins. When I import the .step file into Fusion360 and cut it in half my orthosis is completely filled with material

@Peter_Schmidt

Fusion360 recognises two bodies, but both are filled.

Finite element analysis FEA requires a mesh. Fusion most likely will be turning the step/stp into a mesh at some point, otherwise the calculations will be infinitesimal.

The “filled” illustration you see is possibly just a section-view graphic effect, and not actually a ‘filled’ situation. I can’t think of a single 3D format that has such a characteristic as being ‘filled’. Voxels might be the only thing that could come close. I used to think breps were ‘filled’ but I was mistaken. Nurbs ‘volumes’ might have something like that, but I doubt it.

It’s most likely similar to a hatchmark illustration of a section view.

If there’s actually ‘two bodies’ then you imported something else too by accident? Even then there’s still no format I can think of that would actually be filled. It’s probably just Fusion graphic.

Just import an .stl into Fusion, and feed it a mesh.

Yes it’s possible that Fusion is converting the stp/step behind the scenes into a mesh without telling you in order to prevent infinite calculations, similar to Rhino’s render-mesh.

Instead of using Fusion you may consider:

Intact.Simulation for Rhino Grasshopper – Intact Solutions, Inc.

[Peter_Schmidt]

Thank you all very much for your answers. As my attempts in Fusion were not successfull because the mesh never looked smooth I continued with Rhino.
First I cut off the fingers and elbow part. Now I had an open shell and with offsetMesh and solid = yes I was able to achieve my result.
After using the commands David recommended I was able to export a smooth geometry that looks fine in Fusion. So hopefully my colleague will be able to do his analysis.

Thank you all for your help!