Hey There Guys!

I have a 20m3 sulfuric acid tank made of polyethelene. I have a cut extruded hole on the side of the tank drawn on the front plane. I have to rotate this hole 45° from the front plane with the moving face feature.

But when I execute this command a part of the material just disappears?

Just a simple question: Why?

Can you help me with this problem?

Thank you in advance.