Hi nos - instead of using Sweep for this case, I'd probably try to do an extrusion that has some initial sharp edges and then use Fillet to round them off, something like this (also see attached 3DM file):



With that method you can be pretty free to adjust the bottom profile to different forms.


The problem with using sweep in this way is that sweep functions by basically dragging a profile along the 2 guide rails - in a certain sense it is a sort of tubular construction mechanism since it generates a shape by a series of cross sections. When you have the ends collapsing down especially at a 90 degree angle to each other it kind of becomes an unnatural situation for a tube - it kind of creates a sort of tension in the shape.


Another way to kind of describe the problem that you were seeing with sweep is imagine trying to sweep between these 2 shapes like this:



Because the sweep action works by dragging the profile while marching along each of those curves, trying to sweep with something like this as the rails will generate profiles that connect to each other like this:



So you can see that there's kind of a mess where some profiles sort of backtrack over top of the previous ones just one side, and each kind of messy area corresponds to a place in the wiggly curve where it changed direction to come in at a 90 degree angle towards the other rail.

So that kind of 90 degree angle turn towards the other rail is something that is kind of problematic just with the general mechanism of Sweep, especially when you actually exceed 90 degrees...

- Michael