Failure to Add but forms Closed Intersections

Thanks to the folks here, I have been working to clean up this part. I think all the tangent rails and triangular surfaces have been eliminated at this point. I still have a some work to go. However, I tried add these two closed surfaces together and I get a big fail. I did an intersection on them and the results are closed paths.

I can join the two using splits. I was just wondering for educational purposes why this does not form a boolean union.

Problem Add 2.3dm (970.1 KB)

Hi Jim, it fails here as well, I’ll see if I can figure out why. Thanks for the example.
The parts are .03 thick and file tolerance is .01, that is not a good combination.

The purple thing has a super skinny surface right along part of the intersection:

I’d get rid of that thing and see how things work.