Thanks for taking the time to reply. I really like your design and I can see you put a lot of thinking into making the construction easier without compromising strength. The simplicity of the two solid bars on the top and bottom is a great plan. I'm going to keep a very keen eye on your build to see how you do things. Time for me to start changing my drawing to incorporate some of your new ideas. The only thing I will do different on mine is to not have the rotating ball nuts on the x. Not because I don't think its a good idea but its my first serious build and I'll rather avoid that bit of complexity and go for the stationary x motors on mine.
How are you mounting the spindle inside the z box? Are you making a custom mount or will you just be modifying those standard cast spindle mounts?