Hi Bruno, another thing you might try is to use the long curves as the profiles for the sweep and the short curves for the rails. The reason to try that is that it can be easier to control how the profiles connect to each other by their segment structure. For example here I've rebuilt the corner areas to make them single segments structured like this:



Then if joined together and used as profile curves for the sweep, it will result in those areas being matched with each other and that will probably help get a better shape in those tighter bend areas:



If you look at the surface control points generated from this method in those corners, it looks like this:



That looks pretty good, with things more evenly spread from one station to the next, the things that cause poor quality surfaces are when the stations are kind of diagonally slanting or crossing over each other because of bunching.

- Michael