The fusée (French for “rocket”) is a cone-shaped component connected to the mainspring’s barrel by a chain. As the mainspring is wound, the rotating barrel winds the chain around the narrowing fusée.
As the watch runs and the power stored by the mainspring decreases, the tension from the fusée’s chain on the barrel, now rotating in the reverse direction, ensures that a consistent amount of energy is released through the movement until there is none left.
When winding the movement, the fusee chain would unwind from the mainspring barrel and transfer over to the fusee. As the watch winds down, there is a loss of torque in the mainspring, that’s where the fusee saves the day with “constant force”. The fusee balances out the distribution of force from unwinding mainspring, which in turn improves accuracy.
Shown below are a few pictures that show how a Fusee works:
Mark Sirianni Watch Repair
25 Fraley Street
Kane, Pa. 16735
Charley Photo of the Week: Charley enjoyed the weekend with the grandchildren