Hi ioVideoMaker,

re:
> - sweep with one rail creates a hashtag like surface? why??

Can you please post the .3dm file that you are showing in the video?

But my guess without being able to examine the actual geometry is that it's because you have a non-planar path.

A one rail sweep on a path with sharp corners will attempt to produce mitered corners by extending each section and intersecting them with each other but that can be problematic if you have a path that is not either all planar or made up of lines only.

If you can please post the model file that goes along with your question it can help a lot to better understand what you are running into and give better suggestions.

Probably what you want to do there is trim the surface with your curves, then extrude the middle surface piece.

Thanks,
- Michael