Having 4-row profile rails is an advantage over 2-row - twice the balls = twice the surface area in contact with the rails which should get better stiffness, in addition to factors usually mentioned. However 2-row is still in a different league compared to round rails, so unless you can sell them and get better rails for the same price I think there's other places the money would be better spent on. You've got long rails, so use that to your advantage as if you're prepared to sacrifice some travel you can space the bearing blocks out more to reduce the load on each, so long as the piece they are mounted on is stiff. I got 760mm rails for my Z-axis, so if I ever get round to making it I'll keep 400mm travel and have the bearings 360mm between ends, which is slightly extreme but the rails were cheap so why not.

Quote Originally Posted by Iwant1 View Post


Lost of cnc machine parts are available in the SketchUp marketplace, which you get to from within SketchUp. All the rails, bearings, spindle, motors, ball nuts, etc are available.

The standard part libraries can be helpful, but I tend to draw things myself so I can be confident it is correct. I guess if I used SketchUp I might think differently.