Hi Andrei,

> Why does booleand diff does not work after I made fillet?

It's hard to analyze geometry problems by just looking at screen captures, can you please post the 3DM model file with the objects that won't boolean together?


> <...> In other cases I have not hole but broken surfaces with square holes.

That usually means the trim boundary is damaged in some way, like it has some self intersecting loop in it, or gaps between trim edges or things like that.

- Michael