Hi crydee, I've got a tuned up 3DM model version attached, which should now join without doubling - I trimmed this one surface here so that it kind of matched the surrounding surfaces edge-to-edge better:



So hopefully the attached 3DM file should let you continue on with the model now.

It may take me a while to analyze what exactly is going wrong with Join in your original case, and if it takes too long it might go on my list of things to look at in a little bit when v3 is underway. But thanks for posting the model in the "before" join state so that I could reproduce the problem over here, that helps a lot to give me a better chance at being able to figure out what is going wrong.

I suspect that Join is creating some kind of improper object in your original case, something like a non-manifold edge (edge joined to something like 3 surfaces instead of only 2 surfaces) or a tiny compressed edge, or a boundary with some of its own edges joined to each other, something along those lines. Something that apparently then causes the face traversal that is supposed to gather up just one side of the object to kind of leak over and gather faces on the other side of it as well.

- Michael