One of the biggest probelms I'm having is getting the motor and the thread lined up. After tryng various designs I came up with a very simple solution.
While looking around the "metal laden" (Metal shop) looking for a mounting plate for the Z-Axis I came across "connection pieces" for M8 thread. As I'm using M8 thread these things looked perfect, the only problem is that the stepper motors have a 5.3mm shaft so I had to find a solution. In the end I drilled 3 holes at 120° to each other and cut a M4 thread. So Here's a few pictures:-
M8 connection piece.
With 3 holes at 120°, the actual position of the spindle can be adjusted so that it runs exactly in the middle.
Just see how accurate/centered this runs. Click on the picture for a short video.