Hello guys!

I'm trying to create a thickness to a Joined Surface using the Offset->Shell-command (see attached 3dm file below).
But I don't really understand how to command works, it just gives me this mess:

Would be very grateful for some pointers on how I can make this work

Cheers
Nick

Hi Nick, unfortunately the surface thickening mechanism in the geometry library that MoI uses is pretty limited - it can only really thicken a single surface or one that has right angles in it, not one that has has surfaces meeting at all different angles like you've got there. Those cases add a lot of complexity because pieces that meet all at different angles will make a type of "branching vertex" result. The library does not deal with that case at all unfortunately, it assumes that each vertex in the original shape matches to just one vertex in the offset one. The thickening can work better if you are starting with a solid rather than an open surface, that's a pretty different process.

- Michael

You can kind of get an idea how it's complicated in especially in areas like this:



If you run Edit > Separate on that first and then do a shell of all the individual separated pieces, you'll see that when each piece is individually thickened, the "side walls" between the original and the offset are not really aligned with each other in any good way:




That's the part that's pretty different with doing a thin-wall shell of a solid instead of an open surface, with a solid the "side walls" come from surfaces of the original solid rather than needing to be totally cooked up.

- Michael

re:
> Would be very grateful for some pointers on how I can make this work

Is there any way for you to make it into a solid rather than starting with an open surface like that? That's one thing that may help.

The other thing you could do to make progress would be to use Edit > Separate on it to break it apart into individula surfaces, then use Offset or shell on those individual pieces which will succeed and then work on extending planes so they intersected each other, use Construct > Curve > Isect to intersect those planes to get extended boundaries and then build new planes from those boundaries.

Or you might look at some other CAD programs like maybe ViaCAD Pro might potentially have a better surface thickening function than MoI currently has, if you import your model into there that might work.

- Michael

Thank you Michael for great explanations and suggestions!

"Is there any way for you to make it into a solid rather than starting with an open surface like that? That's one thing that may help."

Hmm well...actually the reason I wanted to create the thickness in the first place was because I messed up the form and wanted to recreate that previous state when it was a solid. So I broke it apart and kept the faces that were correct and thought I would be able to puzzle it together somehow.

"Or you might look at some other CAD programs like maybe ViaCAD Pro might potentially have a better surface thickening function than MoI currently has, if you import your model into there that might work."

I did try in OnShape, but it wasn't able to compute either. I'm going to download the demo version of ViaCad and see if it works there.

"The other thing you could do to make progress would be to use Edit > Separate on it to break it apart into individula surfaces, then use Offset or shell on those individual pieces which will succeed and then work on extending planes so they intersected each other, use Construct > Curve > Isect to intersect those planes to get extended boundaries and then build new planes from those boundaries."

Haven't been able to pull this off yet, I'm gonna keep trying though. This seems like a very useful function, I didn't know about it! Thank you for yet another lesson in MoI :)

Hi Nick, well I'm not really sure what kind of result you're looking for... is it something like the attached model?

That was made by copying over edges and flattening them, then lofting between them, with the hole filled in by drawing in some lines and using Construct> Planar:



If you then take a solid like this into OnShape or ViaCAD you would have a better chance at shelling it using the large planar face as the opening, if you wanted a thin-wall object you'd probably need to build something like the attached version first in order to produce the final shell.

- Michael