shell on surface with nurb-edges (to make a surface solid)

 From:  Michael Gibson
649.7 In reply to 649.6 
Hi flashnfantasy, yes this tends to be a problem with shelling open surfaces that have corners and curved pieces.

There is one older discussion of this that has a similar example here:

If you use Edit/Separate and then shell or offset each piece separately, you can kind of see that the resulting offset surfaces do not connect up to each other smoothly:

This is a pretty tough problem, I'm not really sure what the expected result should be. I guess ideally the offset surfaces should be extended until they meet up cleanly, but this is sort of difficult to calculate in some situations. The problem is that there isn't much in this open surface case to help guide the extensions.

However, it does work well if you shell a solid - this is because when you shell a solid there is an additional surface running along one entire side that can be intersected with the extended surfaces to make the results meet up cleanly.

So in this case your best bet is to build the initial surface as a solid instead - draw some lines to close off each loop and join them, then loft to make this:

Then select the front face, the back face, and the bottom face and run shell, to produce this:

This one now has clean corners:

That works better because when processing the solid since the shelling system is able to properly extend the offsets and trim them back to one common side surface.

So in general if you have corners in your object you'll get better shelling results if you form a complete solid and then shell the solid. Probably it is best to only shell open objects when they are just one single smooth surface piece without any corners in it.

Hope this helps!

- Michael