I have my part fully design, except for the fact the boolean union is failing, meaning there’s probably a gap someplace. Is there a tool for finding this gap or opening?

run ‘intersect’ then invert & hide. The resulting curves should be closed. Use CrvEnd to find the ends.

The command ShowEdges will show any naked edges or non-manifold edges.

http://docs.mcneel.com/rhino/5/help/en-us/index.htm#commands/showedges.htm

HTH

-Willem

Doing the intersect, invert, hide. I see three points in the drawing. They happen to be in places where it looks like the edges come together nicely. Are these points pointing out a problem?

It sounds like there isn’t enough overlap between the parts. There needs to be atleast a small overlap of parts for boolean union to work well. Sometimes it works with co-planar faces.

It turns out the parts Unioned OK, the OP was concerned about some naked edges in the result.

-Pascal