Hi Martin, for your example file you might want to use Loft for that kind of thing, place a top point in the same plane as the last loft profile and use Loft Style = Loose to get a revolve-like rounded tip:






I looked into it a little bit more and it looks like it might be possible to get an exact rail revolve to work with a path like this, it looks like it's possibly a limitation of the geometry library but one that may be fixable. I'll investigate it some more.

- Michael