Very impressed, with a lot of things. Very excited about your A-axis, sometimes one should just go to ahead and build it instead of pondering if it will work or not :D I have not attempted to build it yet, as I dont even have an idea of how I would use it. I really have no clue how one would incorporate 4 axis programming.

I would probably fit the widest possible belt there, if I were to use belt, you want the spindle to be rigid enough. What kind of bearings, if that is how you are pivoting the A-axis? Got any detailed view of it?

Nice work so far.