This is about as straight forward as it gets and yet it fails. So WTF!
Fan_Delta.3dm.zip (1.2 MB)
As may, possibly, have been mentioned once or twice before, coincident surfaces that are not planes are seldom if ever, useful inputs for Boolean operations.
Fan_Delta_PG.3dm (1.2 MB)
-Pascal
Really? Those don’t seem to be coincident planes. They may be coincident construction lines. But up close it seems not so.
The verticle surface to the right is a flat planar surface.
The horizonal surface to the left protrudes into the other object. And apparently doesn’t intersect at the edge of the verticle surface so I don’t quite follow you admonishment.