{"id":69569,"date":"2019-08-02T11:04:30","date_gmt":"2019-08-02T15:04:30","guid":{"rendered":"https:\/\/stockx.com\/news\/?p=69569"},"modified":"2019-08-08T15:43:43","modified_gmt":"2019-08-08T19:43:43","slug":"explained-constant-force-via-fusee-chain","status":"publish","type":"post","link":"https:\/\/stockx.com\/news\/explained-constant-force-via-fusee-chain\/","title":{"rendered":"Explained: Constant Force via Fus\u00e9e & Chain"},"content":{"rendered":"

The most practical watch complications are implemented in ways that make them clear and easy to read for the benefit of daily use. This doesn\u2019t mean all complications are practical (in reality, few are), but their integration to the dial and case design are often contentious considerations for manufacturers and buyers alike. On the flip side of that coin, there are complications which play more of a background role, their overall usefulness not measured by their appearance on the dial or practicality in everyday wear. Examples of this range from the pedestrian, such a power reserve indication; to the ornate, such as <\/span>sidereal time<\/span><\/a>. A more extreme example, is something called <\/span>constant force<\/span><\/em>.<\/span><\/p>\n

Constant force as a concept gets a bit technical, to say nothing of the actual solutions watchmakers have devised to achieve it. Calling it a complication might even be a stretch, but there\u2019s no denying the complexity it can add to a mechanical movement, all for the sake of consistent and accurate timekeeping.\u00a0<\/span><\/p>\n

Before reading further, <\/span>here is some recommended reading<\/span><\/a> that will shed some light on the basics of how a watch works. Title image credit: Ferdinand Berthoud<\/span><\/em><\/p>\n

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The Fusee and Chain mechanism isolated, credit A. Lange & Sohne<\/p><\/div>\n

The term constant force, when used in the context of mechanical watch movements, is referring to the application of a consistent level of energy (force) to the escapement regardless of the amount of energy stored within the mainspring. To put it another way, this component keeps the watch equally accurate from the moment you fully wind it, to the moment it stops ticking. A watch loses accuracy the more unwound its mainspring becomes thanks to something known as <\/span>Hooke\u2019s Law<\/span><\/a>. This drop in amplitude also accounts for the gradual slow down of your child\u2019s wind-up toys. We won\u2019t go into those physics, but watchmakers have developed some ingenious solutions to negate these effects, thus maintaining the accuracy of the watch over the full reserve of power.\u00a0<\/span>The most effective visualization of a constant force mechanism at work is the fus\u00e9e and chain, which you\u2019ll find at work within watches from the likes of A. Lange & Sohne, Ferdinand Berthoud, and Romain Gauthier. A closer look at the fus\u00e9e will reveal a familiar looking device, akin to the gearing you\u2019d see on the rear wheel of on your average bicycle. Like the mainspring of a watch, a rider\u2019s legs are most effective in a narrow band of speed and cadence, as you\u2019ve likely noticed if you\u2019ve ever cycled up a steep hill. Kicking to a smaller gear in such instances provides a (welcome) mechanical advantage to the rider. In this example, the <\/span>conical<\/span><\/a> shape of the <\/span>cassette<\/span><\/a> is the same as you\u2019d find on the fus\u00e9e (though the Romain Gauthier Logical One uses a snail shaped cam). Even the chain is present, albeit much smaller, around the fus\u00e9e, connected to the barrel of the mainspring:<\/span><\/p>\n

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Image via Dionysius Lardner, The Museum of Science and Art, Vol.6, Walton & Maberly, London, 1855, fig.14 & 15, p.24-25<\/p><\/div>\n

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In the example of the fus\u00e9e and chain, as the mainspring unwinds, it pulls the chain from the fus\u00e9e, moving it to a larger \u201cgear\u201d as it goes, so the weaker the pull of the mainspring, the larger\u00a0 the radius of the fusee being used to maintain constant drive torque. This being a highly technical way of saying the following: it keeps your watch telling accurate time as long as it\u2019s running.<\/span><\/p>\n