z axis annoying issues @ prusa i3.Any help appreciated...

Hello,

I have built a prusa i3 and everything works perfectly except from the z axis.I use metric m5 threaded rods,so my steps/mm are 4000 and printing with a .14mm layer height should not cause ribbing.I tried replaced the threaded rod with brass ones and I am also using this to fight backlash.It got better but not as much as I wanted.I've been using aluminium flexible coupling from the beginning.I have even enabled full stepping for the z axis but it did not help.I doubt that my motors are missing steps because when i send the g1 z0 command after the print,the axis comes back to the same place the were at the start.

There's a picture attached from a printed object,

Any help highly appreciated,

Edited 1 time(s). Last edit at 09/14/2014 04:25PM by cuper.

With your aluminum flexible coupling, do you allow the threaded rod to sit directly on the motor shaft? It has been recommended to put a ball bearing or bb in between the threaded rod and motor shaft to allow the coupler to fully do what it's supposed to do.