Secant surfaces won't join

So I’m trying to make a tube go through a closed surface, and join them in a single surface.

I have a closed cylinder representing a Submarine pressure hull and another cylinder, closed on the outer end, representing a torpedo tube. I have trimmed the hull inside the tube in order to make the hull for the torpedo tube. And when I want to join my tube and my hull, Rhino returns the following error : “Unable to join surfaces or polysurfaces.”. Any idea ?

Please find example file attached
example_sub_hull.3dm (107.5 KB)


Hi @loic.lefebvre98
In order to use join, you need to have open (aka naked in Rhino-lingo) edges that coincide, so in this case you need to split the smaller tube with the big one, and delete the part you don’t need - then use join into a closed polysurface. It might be worth going through the level 1 (and level 2) manual, so that you fully understand when and how to use trim, split, join, booleans etc. These are some of the most basic, but also most important, tools in Rhino.
HTH, Jakob

Hi Jakob,

I have done this before and it works indeed, but for export purpose (and structural calculus after) i also need the inner part of the smaller tube…

Hi - as Jakob pointed out, you cannot join surfaces that don’t have coincident naked edges.
Meshes can be joined into non-manifold objects.

Hi @loic.lefebvre98
The you need to either mesh the parts first and join them into a disjoint mesh (if you need mesh or use NonmanifoldMerge, if you need NURBS (and use IGES for export, as STP doesn’t support Nonmanifold IIRC. But beware that many subsequent operations will fail on the Nonmanifold object.
HTH, Jakob

Thank you for you answers !