About this 3D model

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