When I try to use fillet to the object, if I use 0.3 radius, everything is OK. If I use 0.5 then nothing happens probably because it is too big.
When I use 0.4 then... see for your self !

Funny : maybe the HyperSpace o:)

Hi JTB, yup the problem there is with the hole at the very bottom when looking at the top view.

For the weird result at 0.4 radius, you can see that the fillet for the outside edge is overlapping just a little bit with the fillet for the inside of that bottom hole.

Once things are overlapping like that, stuff for determining what is on the "inside" and "outside" of intersection results can tend to get confused.

- Michael

Thanks Michael, I thought it was something like that.It was funny because it was exactly at 0.40 radius