Shell command works very confusing

[dorkehelme]

Good evening!

I'am learning the Fusion360 actually, and I'd like to design a snail for 3D printing. The last part of the object is not easy to manage anyway...

I've two design approaces, by the No.1 the shell command works perfect, by the No.2 it will NOT! The bodies are almost the same, the 2nd has even smaller angle.

The software does not give any advice unfortunatelly, which parameters are probably wrong or what should I do to make it work... It is very crazy...

Thanks for any help!

[TrippyLighting]

First I would try to fix the yellow highlighted features in the timeline.  You likely deleted features in the timeline these yellow features depend on.

It is most likely that the reason for this behavior can be found in the way these parts were designed, so having a complete timeline showing how that was done, will probably help to solve this riddle.

BTW, in general, scaling is an operation that isn't often used in CAD

[dorkehelme]

The yellow features are irrelevant, I've cleard up the design for sharing.
If I build up the object from sketch, the result is the same, the "shell" is not working. I think it is a software bug, there are a lot of annoying things in this software unfortunately...:(

Scaling is important if I'd like to print object in different scales!

[TheCADWhisperer]

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@dorkehelme wrote:

I'm learning the Fusion360 actually, and I'd like to design a snail for 3D printing.

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@dorkehelme 

What does the Speaker in the file have to do with designing a snail?

I recommend that you:

1. Start over in a clean file.

2. Create your first sketch and then immediately Attach your file here for comments before continuing on to the first feature, next sketch.

3. Repeat #2 until design is completed.

[dorkehelme]

I think if I have a "lofted" object with "Fit Point Splines" as guide lines, the angles at the ending surfaces are very important. Unfortunately I don't know how the software calculates the transformations and I have no usable feedbacks from it, except "could not create a valid result" But why??

[laughingcreek]

as you create the shell to the outside your creating intersecting geometry, which fusion generally doesn't care for.  sometimes it can solve it, but at some point it fails.  you can see this starting to happen in the the shell pic of body1 that you posted.

[dorkehelme]

Yes, it is just as well. The software likes it or not, I have no idea when it does or gives an error message. This is very-very annoying... This is why I say (among other things), it's a software with a lot of bugs! I think I must looking for another tool, Onshape or so...

[TheCADWhisperer]

@dorkehelme 

Follow my advice and all will be fine.

You will benefit from step-by-step training.

[dorkehelme · Accepted solution]

My conclusion: intersecting geometries by the shell command must be avoided at all costs, because of the software can NOT handle this situation correctly! Perhaps in the next releases will be better...;) Thank you!

[TrippyLighting · Accepted solution]

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@dorkehelme wrote:

My conclusion: intersecting geometries by the shell command must be avoided at all costs, because of the software can NOT handle this situation correctly! Perhaps in the next releases will be better...;) Thank you!

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That conclusions correct. Most beginners of ANY CAD software learn this quickly. 

It is very unlikely that a new release will improve this behavior as these modeling operations are handled by the geometric modeling kernel. ASM (Autodesk Shape Manager) the geometric modeling kernel used in Fusion 360 is also used in Autodesk Inventor, the flagship CAD product of Autodesk.

I tried the shell command of your geometry in ZW3D 2020 which has a very modern geometric modeling kernel and there shell operation filed there as well for the same reasons. Predictable!

Then I tried this in SolidWorks 2023 and it failed there also. SolidWorks 2023 uses the most recent release of the Parasolids geometric modeling kernel and so does Onshape, Shapr3D, Plasticity CAD and many other CAD systems.

You can of course try to continue banging your head against the wall when trying this in other CAD systems, but my suggestion would be to simply learn proper modeling techniques. 

I don't really know @laughingcreek's professional history but he is a pretty formidable CAD modeler.

@TheCADWhisperer has 40+ years of professional history with CAD tools, several certifications with market leading CAD software and has taught thousands of student CAD and Engineering  at Penn State University over a career spanning decades.
I have worked with CAD and other 3D modeling tools professionally for over 30 years.

If you want to learn, we are here for you. You'll just have to learn to listen ...

[JeanFlower]

It seems we have evidence that there is something about this model that makes this particular shell troublesome.  The shell computes its result working from the surface and curve definitions that make up the model.  If you can supply a design file that has the loft inputs complete, then we could seek out a deeper explanation.  (looks like your 'cleaned up' file removed the loft definitions so we can't see those input curves and loft settings)