Strange behavior with Boolean Difference 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).

Please see the following file: 

Any ideas? Many thanks!
How is your notch supposed to be? From what I experience:


You need to lower down your small cube a bit, otherwise its bottom face will overlap the U bottom face and it's a problem for the Boolean modifier. Now it works well.





For the second shape, it looks like it works correctly, what problem have you encountered?