Hi Bob, I'd think you would want to do a sweep there, but currently the edges don't really match up directly with one another, like for example you'd want this edge to span all the way across:



Currently that edge does not meet up with the other ones, there is a significant gap between their ends:



If you could post a 3DM file with just the curves you are sweeping and the all raggedy result from it, it would be easier to give you some advice on what's going wrong with that - it's difficult for me to pick out these things from your full model file that has everything in it.

Are you maybe selecting multiple edges all across the same station for the profiles? That will make for bad results because Sweep thinks that each profile curve that you give it should be one station along the rails - if you have multiple segments selected it will try to use each one of those as a station independently. You've got to join things like that up into a single curve so that you have just one profile curve per station along the rails.

Here's an example (also see attached 3DM file) where the curves are ready to sweep - select the profile, then run Construct > Sweep and then pick the other 2 curves as the rails:



The more narrowed down you can make your example the easier it is to give you advice on it, so for example if you have a question about why a particular sweep is weird, if you extract just the geometry that's directly involved in producing the sweep and the weird result and then post only that, I'd be able to figure out what you are running into a lot easier.

- Michael