Hi,

I'm designing a small 3D printer and I want to use brass bushings and T2.5 timing belts for X, Y axis: 2 rods and 3 bushing per axis.

I saw in repRap and other designs that usually there are two bushing (or linear ball bearing) in the rod where the belt is clamped and the other bushing slides in the parallel rod, but shifted a litle with regards to the others ones. I tried some of these configurations and I saw that it's not so easy to move the guide smoothly if the bearings/bushings and belt forces are not in the correct position.

My question is: Does anybody know a formula to design this kind of linear systems? I mean, a formula to calculate the position of a 3 bushing (or linear ball bearings) + timing belt configuration.

Thanks in advance.