There are alloys like Invar (64FeNi) that are designed for low thermal expansion. [1] It's used in common products like shadow masks in cathode ray tubes. It

There are alloys like Invar (64FeNi) that are designed for low thermal expansion. [1] It's used in common products like shadow masks in cathode ray tubes. It has a coefficent of expansion of 0.8 [2], so if you run the numbers again it gives a total expansion of the tube of 127', or 63' per end. I don't know the costs or if it would be suitable for this purpose, but it seems to be about 3x as expensive as steel for raw stock. [1] http://en.wikipedia.org/wiki/Invar http://en.wikipedia.org/wiki/Invar [2] http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html http://www.engineeringtoolbox.com/linear-expansion-coefficie...