Here is the tutorial saying to do it like I did. And it was Bjarne BZR
Sorry, Bjarne and rOger, I'm getting old...Latest news:
I found out, what was wrong: The 90units height of the upper hole was too small. Making it 128 worked fine. 8)
Didn't want to test this earlier because now I have to reconstruct almost the whole damn(:oops:) building!
Thanks again