Hi Sagda, here is a version of your object that has been repaired to get rid of those 3 little unjoined edges to make it back into a solid. Booleans should now behave as expected again on this one.

So one thing to watch out for is try not to make curves that are almost tangent to each other but only off by a few degrees. That kind of very shallow crease will tend to make it difficult to fillet later on.

- Michael

Hi Michael,
thanks for the explanation, fixed file and the links(this is gold for me at this learning steps), I'm having a lot of fun learning to use moi and I really love how easy to do is some stuff in terms of just create the concept.
Have a great weekend!

You're welcome Sadga and I'm glad you're having fun with MoI!

- Michael