Why won't these two closed polysurfaces union?

sizecad.3dm (16.1 MB)

They do intersect

Hi Aiden - hm - tough one - there are a lot of places where faces are nearly coincident to other faces - this makes it difficult to get good closed curves of intersection even at a tighter tolerance than what you have in the file. I don’t see a really good way out, here.

-Pascal