When you say "Untrim" in this case of this tube what is untrimed ? Curve? Section ? Surface ? ...
Untrim is "Separate" ?

Hi Pilou, it's this surface here that would be untrimmed, the same one that wants to get extended:



To untrim it, use Edit > Separate on it first to make it an independent single surface not joined to anything else. Then select all its edges and do a Delete. The trimming boundary will be removed and the full underlying surface will be recovered.

The other end that will not be extended needs to be retrimmed.

- Michael

OK!
And this
Extrude --> Boundary Sphere ?

Hi Pilou,

re:
> Boundary Extrude --> Sphere ?

I'm sorry I don't understand this question. The mention of a sphere above was about the Edit > Extend command, not the Extrude command.

- Michael

Sorry I have read Extrude so now i better understand! :)

Empty space does not have to stay empty

:-))

Always amazed by your support - very very helpful tips !