Hi Barry,

Many thanks for helping me out with the model! I'm trying to re-create what you did, just to make sure I understand how it works. Does this sound about right? (And of course, anyone else is welcome to jump in and help too!)

I've attached my clean 3DM curves again.

1. I offset the profile curve at the top, so now I have both an inner and an outer profile curve.

2. Then I Sweep each of these profile curves using the same two rail curves (see vertical ones in my screenshot).

3. That gives me both an outer and an inner surface — with or without Caps on the ends.
3a. If I enable "Cap Ends", then Moi3D only adds a Cap at the top. The bottom is still open. Is there a way to cap both ends automatically?
3b. Maybe related to the above, but I can't seem to manually cap the bottom hole after the Sweep. Any idea why?

4. I noticed you added those double lines at the bottom. How were they used in your process?

5. And from here I'm kind of stuck again.