Hi Mr. Yuri - objects that have surfaces or edges that barely skim over each other adds a significant amount of complexity to the boolean calculations.

In order to calculate a boolean, objects need to be intersected with each other and well defined closed intersection loops are identified and used to cut each object up.

When you have surfaces that skim over each other it makes for a complex intersection case. There are kind of large "zones" of intersection instead of crisp intersection curves.

So because of that it isn't expected that a case with such a significant overlapping surface area like you have here will be able to be booleaned well. It's not too likely to work in any CAD program.

One thing that might help is to keep the overlapping areas to have completely identical underlying surfaces. For your case here it looks like you had a cylindrical like base shape that has some cuts taken out of it. Then after that the object was duplicated, mirrored and rotated , is that correct? The boolean could possibly have a better shot if you generated the second object by mirroring and rotating the cutting objects only and applying them to the exact same base object. When you have coincident surfaces that have the exact same underlying surface that can help.

Also it might be possible to finish your model using lower level surface trimming operations though. To do that you would use Edit > Separate on your objects to break them into individual surfaces and then work with Edit > Trim on smaller areas of the model.

- Michael