On the Zenbot machine, the linear bearings are a bit difficult to take a picture of since you have to dissassemble the machine to get to where the bearings are. In short though, there are two square tube rails on the X and the same is true for the Y axis. There are four plain sealed ball bearings per side (two front, two rear that ride on two faces of the square tube). They are fitted with pins that run through the middle of the bearing assembly and mate up with slots cut in the HDPE. They are not adjustable, but I've run mine for a while now and it is still without slack and running very accurately. Not sure that helps a whole lot, but that is what I saw the two times I took mine apart. This design requires that you have a dust collection system since chips on the rails will bind up the ball bearing assemblies that roll across the flat parts of the square rails. That is why I had to take my apart twice since the chips had gotten on the rail and caused the axis to bind up. The Z axis is made with hardened rods and bushings, so it doesn't suffer the same chip binding problems as the ball bearing design of the X & Y axis. As long as you keep the rails clean, this is an awesome design with very little resistance.  |