Medical Molding - Problem with Boolean Split

Hello Dear Rhino Users:

I am relatively new to rhino and trying to create a medical mold with using Rhino’s flexibility. Rhino has served my purpose incredibly well so far. But I have an important set back. I have a shape that I created with medical Imaging as STL file type.

I took the offset of Initial shape and fitted it in a box, then I took the Boolean difference (cutting obj. was the offsetted initial shape) after that I needed another Boolean operation to cut the mold in to two pieces.

I needed a vertical cut but it is not a straight vertical cut, kind of an S shaped cut. So I created the S shaped surface and tried the Boolean Split and it failed. But when I do the same thing with the initial shape it worked. But I need to split the offsetted version

Hello - your offset object is full of self-intersections. If you run Intersect on the two objects and wait a bit while it figures it out, you’ll see the resulting curves are… messy.