Quote Originally Posted by biketrialsdave View Post
Would there be much benefit/need to double up on these? I.e. two carriages per rail?
Definately. The rigidity will be greatly reduced if you don't use two, since with only one on each rail the axis can more easily pivot (or 'rack') about the center point, i.e. the ballnut, which on the gantry will cause the cutter to deflect substantially.