I have a large problem, my original idea to use 608 bearings on 5/16 rod came unstuck when I found that in most cases it won't be constrained enough plus it sags substantially in the middle, because it is a Y gantry holding the Z axis, thus it has a lot of mass, which I have done my best to minimize.
Such that two people have suggested using proper linear bearings, I believe this is the way to go now, as it is impossible to eliminate all the problems of spanning 500mm on 5/16 rod.
The two options I have found are
linear bearing slide SBR12-1000mm (2rails+4 blocks) (eBay item 250610973493 end time 02-Jan-11 14:05:21 AEDST) : Business Industrial
and
Uni-Guide Precision Linear Slide
The top supporting aluminium angle will be replaced with 20mm 3mm thick aluminium angle.
Ideally the rails will have to be mounted vertically, however I don't know how to affix the belt to it when it is vertically mounted from where it is mounted now.
I'd appreciate any ideas anyone might have.
Else i'll have to mount them horizontally and hope that I can mount the Z axis via some box aluminium