Summary

I did Y-axis moving test.
The results was not good.

The maximum speed was just about 55 mm/sec.
The linear stepping motor was stalled when it over 55 mm/sec.

The linear thread is not straight and it is directly affect to the z-direction accuracy on this type structure.
It makes z-direction waving of bed plate when it move.
I didn't know the possibility of the linear thread would be not straight.

Please refer following link movie.
http://youtu.be/YwmH_hrgCt4

The uploaded file is the y-end idler.
It was slightly modified for more good fit.
The original model was in the following link.
http://www.thingiverse.com/thing:104525