Rhino - Modeling Infinity Symbol

1. Move the seam in the curve away from the intersection, make a Pipe or sweep profiles to make the infinity symbol. This is a pipe.
2. Dup the surface and use SplitSrf to cut it up- delete the parts away from the intersection, leaving an X.
3. Make fillets or blends etc, according to what you need to do, between the parts. Since there are now two parts you can get curves of intersection and trim away the inside parts to make a proper shell.
4. Take the blends and trim them into the original, throwing away the 'X'.

- Pascal Rhino Newsgroup