Let’s call this one complete!
Last night I disassembled the x-axis and z-axis on the "7th" and tightened all of the connections and reassembled the machine. Now that I am running the machine I realize just how tight the machine needs to be for accuracy. I also readjusted the y-axis by setting a bit in the spindle at a fixed Z-axis depth (maximum) and then moving the spindle horizontally to each corner of the y-axis. At each corner I did a fine adjustment of the rails until the bit just touches the table. It is now adjusted perfectly.
Now, I consider the 7th to be "complete." I’m sure it will continue to evolve from here, but it is time to use it for awhile before I do any more work to it.