Hi Mark, thanks for posting the model as well, that really helps to see what is happening.

Burr definitely has the right answer there - during the trim the intersection points were just a teeny tiny bit off so the circle piece you got was not actually a 180 degree piece, it is just slightly over that, so that's where the outline is not closed.

Just in case you have any problems following what Burr said, I have attached an updated file here which should now cap for you.


I can repeat the problem with Trim over here, so I'll take a look at what I can do to make that work better.

- Michael