Hi Mr. Yuri,

> Any idea why it won't work?

I can't really tell what you're running into from just a text description, I would need to see the .3dm model file to give very good advice on that.

Sometimes when objects just barely graze each other it can be a problem getting clean intersection curves, an alternative can be to use Edit > Join instead of a boolean. Join unlike booleans does not try to intersect the objects with each other and remove material, Join only glues things together where there are unjoined ("naked") edges.

Another thing to check is if your big original object is a solid or if it has any naked edges.

- Michael