Linear Bearing for 5/16 inch round chrome plated rod.

thingiverse

This Linear Bearing was designed for a 5/16 inch chrome plated rod. Some of the chrome plated rods that you can find at a local hardware store can be fairly smooth over a certain distance. PLA is a fairly hard plastic and can slide pretty well over a chrome plated rod. The stepper motors used in 3D printing have enough torque to pull linear bearings on a chrome plated rod back and forth even though the frictional forces are higher than when using a rolling linear bearing on a hardened polished rod shaft. If the load on the bearings is light enough you may be able to use a Linear Bearing printed in PLA instead of paying more for Linear Bearings like LM8UU's and Polished hardened 8mm rod shafts. You can also try printing Linear Bearings in other types of Plastic such as Nylon which should have a lower coefficient of friction when sliding on a metal surface. This part was designed using the Freeware version of eMachineShop.