Conversion from mesh to model generates erroneous results

[tom.davie]

App Version: 2.0.13377

Category: Serious Bug

Reproducible: Always

Platform: macOS/ARM 64/Rosetta 2

OS Version: 12.4

Severity: Moderate

Summary:

The "Convert Mesh" operation sometimes generates incorrect geometry.

Steps to Reproduce:

1. Import the attached stl file.

2. Observe the geometry at the southern end of California.

3. Use the Mesh → Modify → Convert Mesh operation, using the Parametric operation.

Expected results:

The generated Model should have identical geometry to the input mesh.

Actual results:

The resulting model has triangle fans inserted in place of correct geometry at several locations, particularly at the southern end of California

[jhackney1972 · Accepted solution]

I believe your issue can be resolved if you "Repair" your mesh first before conversion.  Model is attached.

[TrippyLighting]

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@jhackney1972 wrote:

I believe your issue can be resolved if you "Repair" your mesh first before conversion.  Model is attached.

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That might be the case, but even then, I wonder what method the OP uses to convert a mesh with over 230,000 faces into a Solid Body.

[tom.davie]

Mesh → Modify → Convert Mesh worked just fine after that, thanks.  That'll teach me for ignoring warnings thinking "ah, that's just it telling me there's a ton of triangles here".

I can't say the conversion was the fastest thing ever... but hey, I expected that.

[TrippyLighting]

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Can you explain what you are going to do with the mesh after the conversion ?

What is the end goal?

Using a CAD software for such a highly triangulated faceted mesh is not the best use of any CAD tool! 

[tom.davie]

I agree - CAD software certainly isn't the best tool for this job.  On the other hand, neither is 3D modelling software.  The goal here is to attach this mesh as a decoration to a part which I then need to manufacture.  I've really not found a good workflow in any toolchain for this kind of thing.

[TrippyLighting]

Can you be more specific about:

1. How todo you "attach" it?

2. what part you are going to attach it to?

3. How are you going to manufacture it?

[tom.davie]

The attachment involves using CSG... Which goes, about as well as you'd expect it to go.

The part is a cover for some mechanical parts, it has a couple of mounting points for brackets and bushings, but is mostly a cosmetic cover.

The plan as far as manufacturing is that it'll be CNCed out of Aluminium, but the short term is that it'll be 3D printed.

[TrippyLighting]

CSG = Constructive Solid Geometry?

If you are interest in help with hybrid workflows, then perhaps you need to be even more specific. 

[tom.davie]

Yes - correct, constructive solid geometry.

I'm actually going to go even more general, rather than even more specific (possibly as mistaken as my attempts to make any of this work).

In general, I've been playing around with attempting to create items that are both functional, sometimes mechanical items, that also incorporate artistic elements.  A lot of those artistic elements end up being rather complex geometry.  Sometimes the artistic elements end up either incorporated into functional parts, or actually genuinely functional parts.  The general theme though is that I actually need to make these items.

Figuring out how to integrate the kinds of shapes you'd more typically see in the graphics domain, and actually manufacture them is in general the task I'm trying to wrestle with, and not finding a good workflow for.

[TrippyLighting]

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@tom.davie wrote:

... and actually manufacture them is in general the task I'm trying to wrestle with, and not finding a good workflow for.

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Right!

The method of manufacture often very much determines the method of modeling or geometry.

For example it you would just want to 3D print the mesh, obviously you would not need any modeling software. You already have a mesh.

If you would want to machine the object, you also might not actually need to convert it into a BRep (solid body) , because Fusion 360 can also directly machine meshes.

If you method of attachment requires precise math of the mating surfaces, then you need to consider the manufacturing method of both objects.

There is not one single method for all situations! 

In case of the .stl file you attached you might want to re-mesh it into a quad mesh and then convert that into a T-Spline and then a BRep. there are a number of options available that include other software in the workflow.

This lends itself much more to machining the part .