create a shell

 From:  Michael Gibson
2426.4 In reply to 2426.3 
And by the way, the reason why this other one next to it worked fine:

Is because the path bends more gradually there and the size of the profile is smaller than the curvature of the path, so it avoids that "folding over itself" problem that I showed earlier.

Hope that helps to make some sense of what you were running into at least!

- Michael