Summary

This is a retainer for Eckerput's Z knob for the Z stop. I had typed out a whole description and stuff but Thingiverse didn't save it. so you'll have to figure most of this out yourself.

Instructions

Decide if you want to print out the one with the notch space for the X motor (Z knob support.stl) or the one without. the one without would require you to notch out the space yourself which means you can remove less material. Its your choice.
Print Eckerput's Z knob http://www.thingiverse.com/thing:40078
Print the Z retainer
Drill out the hole to smoothly fit the knob shaft. i used 11/32"
Put them in place as per the picture. use silicone oil if you want.

There should be enough mis-alignment to provide some spring pressure to keep everything tight.

Z knob retainer for Eckerput's Z knob for Printrbot