Hi Toha,

re:
> Anyone knows why it gives different results when i try to make boolean (union) a
> big object with two smallest ones. both details are equal.

Can you please post the .3dm file for this one too? That makes it a lot easier to inspect your geometry to understand what is happening.

From the screenshot it looks like maybe you've got the back of the piece to boolean just barely grazing over the same surface area as the main piece? That will tend to make booleans difficult because the boolean code will try to intersect the surfaces and 2 surfaces that just barely graze over each other can have a complex intersection. You can do it if they are very accurate like 2 planes exactly aligned with each other but it is usually better to make the detail piece push some distance into the main object rather than skim right along the same surface areas.

- Michael