SJX Watches
Insight: The Science of Gear Tooth Profiles
Having explored several concepts related to energy systems in watchmaking, from mainspring barrel capacity to automatic winding and the chain and fusee, our technical series continues with a detailed examination of how that energy reaches the escapement. A vital part of all watch movements, gears are usually taken for granted and generally not given much thought. But upon closer look, gear tooth profiles vary in shape and size. These seemingly minor variations have big implications and reveal various calculated trade-offs. We take a closer look at the different gear profiles used in watchmaking and review their particularities and evolutions over time. History and curves Mechanical timekeeping is inextricably linked to the concept of gears and transmissions. Long before the invention of the hairspring, early craftsmen and horologists were already using toothed wheels in conjunction with weights, verge escapements, and pendulums to measure the passage of time. Historically, gear-cutters were separate professionals who catered to clock makers. Horological lore has it that the tooth profiles used during the 1600s were traced after the thumb’s shape, although it’s difficult find evidence for this theory. The invention of the hairspring marked a step-change in the technical evolution of the watch, and the later development of detached escapements enhanced precision further. These advances revealed transmission problems that had previously been masked by larger timing er...
