The heat treatment of invar

Abstract Even though invar is the most common material used for the pendulum rod in a good clock, it is still a poor material for the purpose because of its relatively poor dimensional stability over time compared with other materials such as quartz or platinum. Invar is usually considered for its low thermal expansion coefficient (tempco) rather than its dimensional stability. Quartz, however, is an ideal material for a pendulum rod, if you can get around the glass breakage problem. There are three types of invar available: regular invar, regular invar free machining, and super invar. Each has a different tempco and is dependent on heat treatment and any coldworking or machining that the part has received. What never gets mentioned and is not widely known is how big the changes from heat treating and machining really are.