Hey Rusty,

"""""""""""I had never heard of the "rebuild" command, but I do see it in the list of additional commands that don't have buttons. I'm not sure I can see any difference from using that or not, but it's probably good practice in general, and probably required in some cases.""""""""""""""""""""""

If you open your original 5 station igs file and select "just one" of the profiles and run extrude on it to view a surface, you cn "SEE" some seam edges. These are also HARD edges (edges which are not tangent.

Running rebuild is a method to remove seams like this and clean up hard edges