Fusion
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John Hackney, Retired
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I am not sure but I do not think Fusion 360 is the proper application to accomplish what you desire. I will let others more versed in manipulation of STL chime in.
John Hackney, Retired
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@bryn.parrott wrote:
As mentioned, the object has already been converted into a F360 Solid Object.
I mentioned the fact that it started as a Mesh STL because that would indicate that it has thousands of faces (because its fully curved) and alsomost no flat surfaces. Thus some obvious ways to do this are ruled out.
1. Converting a organic triangular mesh directly into a solid model is a bad idea for a number of f reasons.
2. A triangular mesh exist has zero curvature and consists entirely of perfectly flat triangles.
Use Autodesk Meshmixer!
@bryn.parrott wrote:
Great response. I'm doing this because I have no choice. Fusion 360 mesh tools are 'ah-hem' agricultural at best.
See comments regarding Meshmixer below.
Being on macOS unfortunately limits choices. Trying to manipulate triangulated meshes unfortunately limits choices even more.
If I remember correctly, Meshmixer was developed by a single individual and that Individual and the software were acquired at some point in time by Autodesk. That developer is no longer working for Autodesk and development has stalled. Now a subset of the Meshmixer functionality has been transferred into Fusion 360, but unfortunately a lot of the very useful functions such as thickening and unwrapping are still missing.
I still maintain what I posted. The chances to get this thickened using the solid modeling tools are slim to none.
I would also think that Blender isn't the right choice for this. Meshmixer has a toolset specifically developed for dense, triangulated meshes.
Blender is predominantly a polgyon and Sub-D modeling and animation tool that works best with quad meshes.
You might find a workflow for triangulated meshes in the sculpt tools in Blender.
A scanned triangular mesh does not have any topology in a mathematical sense. That exactly is one of the problems!
I feel you have either not listened or not understood what we have posted.
@bryn.parrott I will make one last attempt to explain why what you are trying to do is not simple. Just because the need you have with the models is simple to verbalize does not actually mean it is simple to implement.
As you describe your model is a scanned mesh. That mesh consists entirely of triangles. Each of those triangles has a surface normal, which is a vector perpendicular to the surface of that triangle. Thickening and shelling simply offsets the surface along that surface normal by the specified amount.
Triangulated meshes and in particularly scanned meshes that likely have a good bit of noise in the data, meaning relatively sharp angles between the triangles. When the surfaces are offset by too much, these "sharp" angles cause triangles to collapse, or create self-intersecting geometry.
99%+ of thickening and surface offset operations that fail, fail because of that!
CAD software under the hood represents 3D geometry as analytic geometry or NURBs surfaces when they are arbitrarily curved. In solid modeling software those surfaces are stitched together into a BRep. Those are mathematically precise descriptions of geometry, with topology and without finite resolution.
Triangular meshes have two problems. They have finite resolution and no topology. That is the reason they cannot just be converted into curved CAD surfaces.
When a triangular mesh is converted directly into a solid body, each and every of these triangular facets is converted into an analytical surface, which is computationally much more taxing than a mesh representation. As such this is rarely a recommended workflow.
However, regardless whether you try to simply thicken a mesh ( for example Shrink/Fatten in Blender) or try or thicken a BRep CAD model , the issue is collapsing geometry and self intersections. Based on over 30 years of professional use of CAD and other 3D modeling software I can say that this isn't unique to Fusion 360.
What is unique to Fusion 360 is that Autodesk has started transferring some functionality from Meshmixer into Fusion 360. That transfer is far from complete and AFAIK does not include the mesh specific functions for offsetting and thickening triangular mesh geometry.
Also, Meshmixer was developed independently of CAD software and specifically to deal with triangulated mesh geometry.
That is the reason we recommended Meshmixer.
Of course there are other possibilities to create what you are looking for,
The triangulated mesh can be re-meshed into a quad mesh, which then can be converted into a T-Spline and then BRep/Surface model. Then one could possibly use the shell function. But there are multiple caveats and gotcha's with such workflows.
For example, in order to be able to offset a surface you need to limit curvature (to avoid said self intersections) so it might be necessary to smoothen the mesh, either as a whole which might result is loss of detail, or locally which is very labor intensive and usually requires multiple iterations.
That is exactly what the nice and helpful support engineers at Autodesk are dealing with, and why they have not yet found a solution.
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