Grouping upsets simple boolean difference

boolean difference a cylinder from a cube and it fails, if the cylinder is grouped to a non closed shape !

if its grouped to a simple cube sitting above the item to be ‘differenced’ it works.

Why should a grouping of solid and non solid fail when the non solid is not part of the required cut ?

(ignore the crude incorrect fillet, just a visual effect)

see attached.

grouping upsets boolean difference.3dm (203.8 KB)


Hi Steve - this is because the shallow box is included in the selection that way, and the Boolean first unions the cutters before subtracting the result from the box. Since the shallow box is messed up by the trim from the fillet, that union fails. Make a clean closed box and it will work.


I never realised it tries to union all items in a group, as they might not all be solids.

ungroup I guess, or could I sub-select just the cylinder ? Would that work ?

Not sure right now as I type this how one subselects, ctrl click or ??

I also could do with knowing how to select an item when another one is in the foreground , brain rusted up from being away from Rhino a while.


Crtl+Shift-click is sub-object selecting.
Yes, that will work with Groups so you can make an intelligent Boolean selection.

Hi John,
I was about to post saying sussed it, you beat me to it.

it works