Hi, thanks for replying.
Firstly the carriages have bearings below. The carriages are mounted to flat bar, there are 6 bearings in total in each carriage. Full details are available at www.cncrouterparts.com.

With regards to the pillow block bearings I agree, the final design will include a central block bearing on each shaft to stop flex when applying tension to the belts.

I will re-model the frame to include the Y but I will include rhs instead of channel. The designer has a video if the machine here http://www.youtube.com/watch?v=7XwM_...=youtube_gdata

I'll get some other drawings put together, thanks guys, much appreciated.