Hi Andrei,

> You mean second surface only for hole? Or for area around it to?

The second surface is for the "side walls" of the hole - it would stick out and intersect the outer surface and you'd trim both surfaces with each other.

Then the area right immediately around the outside of the hole comes from filleting.



> This is not clear for me.

Basically cutting a chunk away from a larger block with a curved cutting surface something similar to this:








- Michael