Hi Will, yup it actually takes a fair amount of additional programming to handle the sharp turns. It involves extending the portions along each segment and then doing a mitered intersection to make the corner. Rhino has special code in it to handle this.

I started to work on it at one point, but it was taking quite a bit of time so I postponed it for a while, I don't think I will be able to squeeze it in for V1 but it will definitely be coming at some point after that.

For the 2 rail workaround method, you may sometimes want to put the rails on either side of the shape too - here is another thread with some info: http://moi3d.com/forum/index.php?webtag=MOI&msg=428.12

- Michael