SJX Watches
Insight: A Look At The Fusee and Chain
The fusee and chain system is one of those terms in high horology parlance that instantly elevates the status of a given watch. And yet few appreciate the elegance and subtle complexities of this horological contraption that surprisingly predates the invention of the hairspring itself. The need for constant torque A high-performance oscillating system requires a somewhat constant power source in order to keep it swinging consistently. This issue relates to isochronism and the insufficiencies of real-world oscillators. For a watch, this means that its precision is, to a degree, dependent on how constant the torque reaching the escapement is. This is not as easy as one might think. The mainspring stores potential energy in its wound coils, which it then slowly feeds into the gear train as the barrel unwinds. Because of how the system is built, and due to physics-related constraints, the power coming from the mainspring barrel is all but constant. Ideally, the torque would be linearly decreasing — meaning that the slope of the barrel torque is directly proportional to the arming angle. Coiled mainspring inside a barrel. When a mainspring barrel is fully wound, the torque it feeds into the going train is maximal, sometimes causing the balance wheel to swing too wide and over-bank. As the mainspring unwinds, the torque stabilises to a steadily declining rate. But as the movement enters its last hours of power reserve, the torque from the barrel decreases considerably and more...
