Hi Jim, the booleans are more oriented around working with solids. If you have open surfaces instead of solids then usually the best way to handle those is to use the Trim command instead of the booleans.

The trim command will cut the surfaces of objects and let you pick which pieces to discard. Then you can join the results together.

You can kind of think of the booleans as kind of automatic macro version of trim + join where it decides which pieces to discard from the trim by which volume they are in. But if there are no volumes to the pieces then the lower-level plain Trim is better.

See this recent post for a description of how to do a "Mutual trim" where you want to cut 2 pieces with each other:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3901.5

But also you may run into some problems trying to merge your piece there because it looks like one of its corners may be badly formed and kind of bunched up and potentially folding over itself in this area here:



Those kinds of mangled chaotic surface areas tend to cause problems in surface/surface intersection calculations that are part of the Trim and Boolean commands.

So that surface may need to be reconstructed to be cleaner and not bunched up in that area before it will really be suitable for trimming.

- Michael