Im in to build one.
I will use nema17, spectra or t2.5 belts and the new z axis, with an m6 rod.
I will get some 10x10 alu square tube and do some tests with the printed carriages, to see if i can get them really tight.
Any hints or recommendations?
If you need help to develop and debug qr14, i will build that, but with nema17, t2.5 belts or syncromesh or spectra. With that restriction the only thing i have to buy is the alu tube. I dont have any nema14 and i dont want to spend more money 
Spectra == Dyneema == fishing line
synchromesh: http://sdp-si.com/web/html/newprdbelts6.htm
And what is the way that this will be work?