Hi Satoribomb,

I see now where that particular micro edge/surface came from. Your flange box ended right at a spot creating this kind of a situation between a box and a circular piece:



It's that type of a relation that caused those little slivers in this case.

Often times it is difficult to guarantee that different pieces meet up in a simple way. That's one reason why it is often times a good idea to generally make boolean pieces overshoot each other by a fair margin instead of having cutting pieces try to match exact lengths.

I guess applying that advice to this particular situation would mean extending your flanges like this:



To do that, I extended the box until it was sort of completely poking out through everything on that side. This avoids the micro edges, and the boolean will succeed:



However, you can notice that the coincident/overlapping areas that I showed in red in that earlier post have sort of left some of their edges behind. This is hard to avoid, when there are overlapping pieces it is difficult for MoI to always produce the optimal result that you would like, sometimes different edges of all the pieces will get incorporated into the final result. So to make a really clean result I would still recommend extracting out that central section and doing the cut just on that and then recombining pieces later. Avoiding the overlapping areas just tends to guarantee you cleaner results.

- Michael