A mainspring is a coiled metal strip, usually of spring steel, that powers a mechanical watch. Winding the crown or a key tightens the spiral and stores energy in it. As the spring slowly unwinds, it gives that energy back over time through a chain of gears that drives the movement.
How does a mainspring work?
Fully uncoiled, a mainspring is a long, narrow strip of metal, roughly 20 to 30 cm in length. Wound up, it sits tightly coiled inside the barrel. In a typical one-day movement, the spring is sized to run the watch for 36 to 40 hours before it needs winding again. Self-winding watches use a different fixing at the outer end. There, the spring is attached to a slipping expansion spring called a bridle. The bridle presses on the inside wall of the barrel.
Where it comes from
Mainsprings were first used in the earliest spring-driven clocks, made in Europe in the 1400s. The Nuremberg clockmaker Peter Henlein is often named as the inventor, but the credit is disputed. One older way to even out the spring’s force was the fusee: a cone-shaped pulley, driven by a chain wound around the barrel. In 1760 Jean-Antoine Lépine invented the modern going barrel. It gives an even force by using a spring longer than is strictly needed.
What are mainsprings made of?
Older mainsprings were made of carbon steel. Since 1945, carbon steel springs have gradually been replaced by newer special alloys. Some makers use their own proprietary metals. Two examples are Seiko’s SPRON and the Swatch Group’s Nivarox. Modern alloys also bring a long working life. A mainspring made from an alloy such as Nivaflex can last 20 to 40 years in normal use.
Checked