oldham Z coupler for RepRap with downside z motors

video: http://www.youtube.com/watch?v=Bc-pEWRrJsc&feature=youtu.be

this coupler will compensate small or lages align errors between z treaded rods and motor shaft, the middle piece will do it by moving itself, if the rod is out of centre of 5mm will work too!! soon a photo of printed item :)

if the print head touch the printbed after a few turns the coupler will not pull the rod because it will disassembly, is a sort of z-saver, but i i have design another version for upside motors wich bl