This version is no-longer being maintained
please use the V2 linked below as it is soo much better.
Even if you only use the updated top plates it's still so much better.
V2 is here http://www.thingiverse.com/thing:1470886
new parts include updated top plates with more adjust-ability for belt length, and a 18t stepper pulley and updated 36t pulleys for the z lead screws (so a 2x improvement in torque)
you may wish to refer back to here for construction tips and parts, as V2 is very similar (with the belt setup)
old version please move on to V2 (http://www.thingiverse.com/thing:1470886) if you can as it is much better..
This is a z axis upgrade for my zonestar p802 I3,
this features a top plate with a stepper motor mount, 608 bearing hole for the z lead-screws and slots for idlers, to adjust to a standard length of belt.
This has fixed the issue of having to re-align the x stage of my i3 each time I wanted to print.
I had a problem with the blank shaft connector rubbing the z guides, so have updated the part to V2 and made them a bit smaller in diameter.
for this you will need the following parts,
2x 8mm toothed pulleys
1x 5mm toothed pulley,
1 belt (GT2 2mm Timing Belt 976mm x 6mm (488 teeth) )
2-3x idler pulleys
3x idler standoffs
2x 8mm shaft couplers (to clamp underside of Z lead-screw) - now V2
2x base mount (to stop 8mm shaft from falling though, this replaces the bottom mounted stepper motors)
7x 608 ball bearings
M8x50 bolts (for idlers)
M8 studding (for re-enforcing)
M8 nuts (I used a mixture of Nyloc and regular)
M4 nuts and M4 grub screws (to grip shafts form pulleys)
misc M3 nits/bolts for belt tensioner
I may make a bottom bearing for the z lead-screws (which is why there is an 8mm hole directly beneath them) but if they are not needed then I won't bother.