Is this the one?
http://www.youtube.com/watch?v=uRM8iHxuM58&feature=related]Fine Line Automation FLA-100 Build Part 2 - YouTube
I have to say and I'm no expert but the bearings components tracks are rather a crude method of travel.
I mean putting bearings on nut&bolts as their shaft is extremely fred flintstone methods.
Bearings should be on precision shafts with a tight tolerance fit.
Just my ten cents worth mind.