Summary

This is a shell for encapsulating a 3/8â€ rod with BBâ€™s to act as a linear bearing. The use of NYLON makes it possible for the bearings to provide both support and a smooth rolling movement across the rod.
This part is made possible by the 2BEIGH3 3D Printer as outlined at:
http://www.instructables.com/id/Combination-CNC-Machine-and-3D-Printer/

Instructions

The stl file is for discussion purposes only as it is configured for a NYLON cooling gradient as printed on a 2BEIGH3.

While initial builds of the part were successful, the BBâ€™s eventually became problematic. It was discovered that not all BBâ€™s are as spherical as they appear. For best operation, and to keep cost down, the BBâ€™s were washed and then sent through a centrifugal sort.
As seen in the photo, there are some remnant threads in that retraction was not used. As the material is NYLON, they are not affected by acetone. The part was rotated in CAD such as the threads would not be in the raceways after being processed by slic3r.
Each unit uses 20+ BBâ€™s and because the part is made from NYLON, no lubrication is used or needed.
The print nozzle for these parts was a .5mm. The course nozzle was responsible for a few BBâ€™s (2%) that did not make proper contact with the rod.
The part is designed for a fluid mixing system that will automatically test water samples from various wildlife sources. pH, ORP, TDS, chlorine and certain industrial residues will be measured and documented. NYLON is the material of choice as itâ€™s not subject to chemical degradation by most of the test reagents. NYLON also requires no lubrication that can contaminate the test samples.

For this part a common type of NYLON was used and for over-all rigidity, the fill was increased to 65%.
The part may be referred to as a derivative of http://www.thingiverse.com/thing:4718

Simple Linear Bearing from NYLON