Hi Paolo - the hood.3dm file that you posted is pretty much a different kind of problem than that previous one.

You have probably seen that you get the same kind of pinched tip result in Rhino as well with that curve arrangement.

That's caused by having pretty different shapes and lengths of curves be forced to collapse together into a "pole" point.

The shapes vary quite a bit in curvature, the ones on the sides are drawn out to be longer and the one in the middle bends more sharply at the end. With all of those coming together into a single point you basically end with a kind of averaging effect which produces that kind of shape.

Instead of trying to force curves with differing shapes together into a single point, it tends to be better to build a larger extended sheet that does not pinch together, and then use trimming to cut it off to make its final edge rather than trying to surface directly along a kind of an irregular juncture.

The sort of general technique that you're using there of building things only directly off of the final edges is something that can tend to work more easily with sub-d modeling rather than with NURBS modeling, when the pieces are all supposed to be smooth with one another.

- Michael