I am designing a rather complicated system that needs a certain level of precision. The design includes four (probably aluminum, possibly steel) threaded rods (1/2" diameter, 15" long) in the formation of a square that will support a load of around 6 pounds (load may vary). The dimensions of the centers of the four rods is 1.6" X 1". How much flex will I see from the aluminum or steel rods and what kind of stiffness should I expect? Since the load will be changing, I would appreciate any formulas that might apply. Thanks.