A problem to fix first, for some reason the z axis is stopping about 5mm up, makes a grinding like noise... both motors stop.
I changed it to 1/16 stepping, whisper silent, works, but still stopping in the same place. I'm going to check the captive springs, they might be jamming somewhere. It appears that the hexagonal holes the 'captive' nuts on the threaded rods are too big.
17.(optional) Insert a spring into the top of the hexagonal channeloh, apparently it's optional I guess I could try without the springs. In taking it apart I found the ends of the springs were jammed into the top nut on one side, and the threaded rod hole on the other.
Yup, the springs were the problem.
Pictures to come...