Boolean Union creates Transparent Surface

I ran into this unusual situation so I thought I would share. In the attached file—

Problem Union.3dm (298.9 KB)

—I have three closed polysurfaces:

If I add them together, they produce this transparent surface. If I run the various checks, nothing appears wrong.

It appears that the surfaces are transparent on one side and opaque on the other side.

Hello - yeah, the cylinder surfaces have zero width where the pipe cuts them right at the end caps -

if you rotate the cylinders so the seam is right there, or split them in two there, it should be cleaner.


I should have mentioned that a 90 degree rotation gets rid of the problem. However, it seems like there should be some diagnostic as this would appear to be a bad surface of some kind.

I am having trouble with this same problem and don’t know how to fix it. I have “flowed along surface” a set of 3D letters that cut through the outer surface of the target object. When I boolean union target object and text, one half of the target object becomes transparent. The same happens if I split and join. It would be great if someone could explain what’s happening and how to solve the problem.
Collab Grip model.3dm (8.1 MB)

Hello- DivideAlongCreases > SplitAtTangents=Yes on all the stuff before flowing it, the results will be much cleaner.


Thanks but that hasn’t cured the problem, Pascal



Your advice to “DivideAlongCreases > SplitAtTangents=Yes” certainly helped but the base problem was the TAPEDESIGN logo. After I cleaned it up, everything worked fine.

Thanks for your help.