Summary

Spring coupler with 5mm and 8mm shaft diameters

Based on parametric scad (file included)
A remix of this: http://www.thingiverse.com/thing:268468

Made out of desperation until I get a metal one!

Instructions

There is not much clearance with the motor mount bolts so you need to trim the M3 screws with a file or grinder. If you put 3*M3 nuts onto the screw it gives about the right depth.

The scad produces a non manifold output but it slices ok at the given settings. If you change a setting then check your slice before printing. The included stl slices ok.

If you modify the scad, the largest bore diameter must be the #2 diameter which is at the bottom.

5mm shaft needed drilling out a little to clean it up.
The M3 nuts are slightly loose in the holes.

Repetier 0.9
No support required :-)
190C 55C PLA
2mm brim
0.3mm layers
25% honeycomb infill
70mm/s fill
40mm/s perimeters
30mm/s outer and tight perimeters
200mm/s acceleration

About 30mins to print

K8200/3drag z-axis leadscrew flexible motor coupler