Hi Pilou,

> I have a trouble: how do you make the the curvated surface
> after make the "flatten" curves and offtseted them?

That's by doing an "Untrim" on one of the original surface pieces.

Take one of the original curved surfaces, delete all the other ones, use Edit/Separate so you are dealing with just a single surface.

Now select all the edges, and hit delete to remove them and recover the full underlying surface - that's how I got back the original larger curved surface to trim.

The original is wide enough in one direction to cover the new larger outline, but not in the other direction where I added the lines.

- Michael