After playing with this puzzle for a few days I’m really happy with how it turned out and I think the above improvements will make the next version a little bit better.  This reminds me of Forrest Higgs’ recent commentary on engineering with a RepRap in the design cycle.  It’s so easy to test out a new design that I don’t hesitate to whip something up, print it off, SEE and FEEL how it works and any unintended nuances of that design, and then redesign with these revelations in mind.