I ask because I'm thinking about upgrading my Printer and doing some research and found out that for a linear motion a hardened rod should be used, when using ball bearings. I looked at the robo X-axis and saw a lot of scratches on the surface. The Diameter seems also a bit to much under 8mm (I guess they should be 8mm) about 7.9 to 7.95. *Edit maybe i just measured not so exactly the first time, now i get 7.98 to 8.00, so I'm not so sure)* The sledge (the thing that holds the ball bearings with the print head) also has a lot of backlash (moves around while the belt is not moving). Does anyone know something about this?