I'm getting strange behavior with Boolean Difference as per the attached file.
I'm trying to cut a notch into the U-shaped object using either of the two shapes on the right.
With the more complex shape, I can't get a notch at all.
With the simpler shape, I can get a notch, but not when it's exactly flush with the U-shaped object (I want to do it when the cutting shape is flush).
Any ideas? Many thanks!