Walk into most any Ace Hardware or hobby store and you'll find an assortment of hollow tubes in different sizes and metals I've chosen to update my Smartrap to use these craft tubes as smooth rods. I find they have a number of advantages over the conventional solid smooth rods. They are: The tubes come in different sizes. Smaller sized tubes can slip easily in and out of larger tubes with barely any play between them. This means that the tubes can also make suitable bearings. Bearings made from these tubes are smoother than printed bearings, but are cheaper and much easier to source than LM6UU bearings. For the Smartrap, I use 7/32" brass tubes for smooth rods and 1/4" aluminum tubes for bearings (shown above). The bearing tubes are a few hundred microns larger in diameter than the conventional 6mm id bearings, so some adaptation is necessary. I've uploaded the adapters I use to convert the LM6UU bearing holders for use with the 1/4"" tube bearings. 9/8/14 - So I've finally updated my smartrap and tested the rods. The y axis works beautifully - very smooth, remains level with the ground even without use of glass supports. The x axis I've had consistent problems getting to be level with the ground, however I increasingly suspect the problem lies with some of the other updates I've made. Somewhere between version 0.45 and the present the Smartrap reduced the number of components to the bottom plate, and now it seems there's nothing in place to keep the z axis rods plumb with the base board.