Hi Mala,

re:
> The boolean operation works for the point but not for the 3...hmmm´...why?

A couple of different things - one is that your base object is not a solid so you will probably need to use Edit > Trim to cut it instead of booleans. Booleans are based on determining which pieces to keep and which to discard based on what solid volume they are contained inside of. When your base object is not a solid it will have difficulty doing that job.

Then also looking at the underside of your object, it's not good to boolean objects that are barely skimming over the same surface area, for a boolean it's better for objects to push through each other by some amount instead of barely skimming each other:



- Michael