Why does the shell tool remove geometry from the other side of my model?

[garywoodhouseweb]

Let me preface this post by saying that I am a beginner with Fusion 360, however I have been using other 3D design tools for a long time.

I have a fairly simple hexagon model, split roughly into two halves. I want to add a hollow pocket into one side of it which is currently solid. The other side has some details essentially opening it up, with a couple of 'legs'. When I add the pocket to two faces of the solid half using the shell tool, I notice that the other side of the model begins to get geometry removed, proportional to the inside thickness of the shell. I've shown this in the recording below.

How can I prevent this from happening, and contain the shell to only the solid section of the model, and not the legs?

https://autode.sk/3jEJRjB

[jeff_strater]

@garywoodhouseweb - can you share the model here?  It seems that there might be some geometry here that is not apparent from the video.  Thanks.

[garywoodhouseweb]

Sure, here you go.

Thanks for the assistance!

[jeff_strater]

thanks for the model.  Yes, there is something definitely weird with that shell.  Shell is not supposed to do that.  Might take a bit of research to get an answer...

[garywoodhouseweb]

Thanks Jeff, I appreciate the help.
I'll await your findings.

[garywoodhouseweb]

For what it's worth, I found a workaround to the issue. I would sure like to know why the issue was occurring in the first place though.

https://autode.sk/3gZGWAp

[mango.freund]

hello @garywoodhouseweb  the "shell command" involves the entire body. To prevent this, I separated it and only reunited it after "shell".

greetings mango 

[garywoodhouseweb]

Thanks for the input Mango. This is the workaround I ended up using as well. See my screencast for my somewhat less clean attempt 😛

[TrippyLighting]

I looked at your model and I think what is tripping Fusion 360 is the particular area where the overlap between the center cutout and the patterned instances create an opening in the two legs:

If you change the width from 17.4 to say 17.2 that opening is not created and shelling works fine.

[jeff_strater]

@garywoodhouseweb - the original model did reveal a bug in the shelling algorithm, which the kernel team will investigate a fix for.  But, please use @TrippyLighting's fix.  I suspect that same area of the model is what trips up the shell algorithm.

[davebYYPCU]

There are a few more dimensions in this sketch that don’t match the exercise, 

original was 7 mm tall, not 7.10 mm.  Depth of cut should be 10 mm, but have not check the file, as my version did not break through.

Might help.....

[TrippyLighting]

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@davebYYPCU wrote:

Might help.....

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How ?

[davebYYPCU]

 Might help is my signature, because I can’t say what the reader is going to do with my information, 

This article appears to be similar to a recent Autodesk Youtude video.  There are a few altered dimensions in that sketch, so, there may be other changes that influence the break through, you highlighted, that did not eventuate from the supplied dimensions.  I can check the file later in the day, but my contribution 

Might help....

[TrippyLighting]

Fair enough. I misread the intention of your post!