CBY Z motor coupler M6

v4.2 :
This time inspired by jwest007 Taz Z motor coupler, replacing M3 nut hole by a simple hole for M3 heatset insert.
I also added some support at M6 nut hole entry for good bridging at the edge.
The Freecad model is not really "clean". I'll redo it from scratch later.

v4.1 :
Initaly this thing is a mod of Eric's improved Z axis coupler.

I reduced a litle bit the M6 nut hole. 10mm wide and 1mm smaller for height. This to be closer to the one I intend to use.

I enlarged one M3