Thank you for considering this issue.
I am trying to 3D print a handle that will have a wire running through. As such, I have two meshes to make this handle hollow on the inside: the outer mesh is sculpted (complex) the other mesh is a simple geometric form that is meant to be the inner form of the handle. I have attached images to make this clear.
So far, I have tried to Join them using the Boolean Direct Union operator, but to no avail. The outer form is complex, so it has many vertices. That makes it difficult to join edges or vertices.
My problem is that I want to have this sculpted mesh as the outer form of this object, and the geometric hollow cylinder as the inner form of this object, but I have found no way to combine these two without manifold issues for 3D printing. Ultimately, I need a .stl file for this object.
Any advice would be very much appreciated.