Hi Olga - your cutting surface tube has some badly formed areas where it is folded and crossed-over itself ("self-intersections"):







That kind of surface where it folds back and pushes through itself will cause problems with operations that need to do surface/surface intersection calculations such as the booleans.

In order to get a boolean there you'll need to create a tube that doesn't have that kind of self-interesecting area, either you'll need to create a more gently curving path curve that does not have a bend in it tighter than the radius of the circle for the tube, or you will need to build your tube in some sections instead of doing it all in one go.

- Michael