In Depth: Escapements

By A Collected Man

At first glance, understanding the mechanics of a watch movement can seem a daunting task, with the sheer volume of rotating wheels on multiple levels, having the tendency to make it appear more complex than it really is. Naturally, there are movements which escape simple explanation, however, in straight-forward, time-only movements, the principles are relatively easily grasped. A time-only watch will consist of three main elements, firstly, the power source or ‘mainspring’. This hollowed out cylinder contains a strip of metal which is coiled around a centre-pinion, storing kinetic energy from winding the crown. The second element is the ‘gear-train’, which transfers the stored energy through a series of interlinked cogs, finally connecting with the third key element, the escapement. The job of the escapement is to regulate the release of energy from the mainspring, in a reliable frequency or beat, but it is also required to give the balance wheel an impulse to maintain oscillation. These two principles are essential in understanding the mechanics of the escapement mechanism. 

 

Watchmakers for hundreds of years have been inventing curious new approaches to the design of the escapement. The earliest known design dates to the 13th century and is commonplace in particularly old clocks and pocket watches. This design came to be known as the ‘Verge Escapement’, and to this day remains a mystery as to who originally invented it. These escapements were fundamentally flawed and would eventually become obsolete, however, the principle of the invention would change watchmaking forever. In this article, we will take a look at four prominent escapement mechanisms, starting with Thomas Tompion’s ‘Cylinder Escapement’.

 

Thomas Tompion's Cylinder Escapement. 

 

The principle of Tompion’s escapement was quite elegant by comparison to the more commonly seen Verge escapement of the time. The mechanism was made out of a toothed escapement wheel, a partially-hollowed cylinder, and a balance wheel with a coiled spring. This balance wheel, which is not illustrated, would sit atop the cylinder, with both parts moving in unison. As the cylinder rotates counter-clockwise, the leading tooth on the escapement wheel is met by the outer edge of the cylinder. The coil in the balance wheel absorbs the energy and springs back clockwise, the cylinder rotates and the escapement wheel advances, only this time the tooth is met with the inner-wall of the cylinder. As the balance wheel rotates for a second time counter-clockwise, the tooth on the escapement wheel is released and the cycle continues. The design of the teeth are made in very precise shapes and angles as, for the escapement to continue to beat, the cylinder needs to receive an impulse from the mainspring to activate the motion of the balance wheel. One additional benefit to this design, was that it enabled a much thinner overall case size, as it was far more compact than other mechanisms of the time.            

 

 Thomas Mudge's Lever Escapement.

 

Next up, is the lever escapement, which has come to be the most commonly used design of all. The inventor of this mechanism was Thomas Mudge; a celebrated British watchmaker who studied under George Graham, and went on to design many complex components which would enable the creation of the perpetual calendar, the minute-repeater and of course, the lever escapement. The lever escapement works in a similar principle to the cylinder escapement, however, instead of the escapement wheel directly interacting with the balance, Mudge decided it would be beneficial to place a jewelled pallet-fork between the two components. This meant that the balance wheel was only engaged with the mechanism during the split-second it swings through its centre position. This reduced overall friction, and enabled a far superior timekeeping ability, not to mention the increased lifespan of the parts. While the lever escapement improved upon previous designs, it wasn’t without its flaws. The mechanism required lubrication, and during this time, it wasn’t especially easy to get your hands on quality oils that wouldn’t degrade rather quickly. Nowadays, with quality lubricants readily available, the lever escapement can function comfortably year-on-year, with only very occasional servicing. If you are currently wearing a mechanical wristwatch, the likelihood is that it makes use of this escapement, that is, unless it contains our next example.

 

George Daniels' Co-Axial Escapement. 

 

The Co-Axial escapement has been the only major disruption to the lever escapement’s unbroken reign. It was designed in the early 1970s by master watchmaker George Daniels, and unlike many other complex escapements, which exist in high-end watches, the destiny for the Co-Axial would be with Omega, who adopted the technology in their mid-level watches. The Co-Axial was designed to negate the requirement of any lubrication what-so-ever, and is achieved through a mechanism which would deliver the same basic principle, but with almost no friction at all. The key element is that the escapement uses two wheels sandwiched together, rather than the traditional single wheel. The mechanism works with four jewelled teeth, three on a lever, and one on the balance stem. On the lever, the central tooth engages with the smaller wheel, while the outer two engage with the larger. As the balance rotates clockwise, the fourth jewel, mounted on the balance stem, receives an impulse from the larger wheel, to maintain oscillation. On the opposing rotation, it receives its impulse from the smaller wheel on the central tooth on the main lever. Each oscillation locks and unlocks the motion of the escapement wheel. The difference between this and a traditional lever escapement is explained by Daniels as more like the opening of a door, rather than two surfaces sliding against one another to give the impulse. The one critical flaw in this design was that it is incredibly difficult to place the two separate wheels together perfectly. Fortunately, the legacy of the Co-Axial escapement has fallen on the shoulders of Daniels’ only apprentice, Roger Smith, who ingeniously designed a single wheeled version. This single wheel would incorporate the two levels of the cog as one item, making precision and manufacturing far easier than before. The reduction of weight also had a positive impact as it would require less force from the mainspring to operate, giving the components a far greater lifespan.

 

François-Paul Journe's Natural Escapement

 

And finally, we arrive at François-Paul Journe’s Natural escapement or ‘Bi-Axial’ escapement. The natural escapement was originally invented by Abraham-Louis Breguet during the previously mentioned horological era which struggled to find quality lubricants and oils. According to scholars, Breguet produced twenty prototypes using his natural escapement, some of which using two escapement wheels, in a design not totally dissimilar to the Co-Axial escapement. His designs across the twenty pieces were each slightly different, and it’s said that the concept was abandoned because the level of accuracy required surpassed the manufacturing capabilities of the early 19th century; put simply, it was too expensive. With modern manufacturing capabilities, it has become financially viable for companies to produce natural escapements, with examples being made by brands like Laurent Ferrier, Kari Voutilainen and F.P. Journe. The above example is from François-Paul Journe’s Chronométre Optimum, and is quite possibly the most visually complex of all the examples we’ve shown. The key to this mechanism is that it uses two escapement wheels, reducing the overall force required for the movement to function. Part of François-Paul’s philosophy is that the watches he manufactures should still function in 200 years time; a principle he shares with his greatest inspiration, Abraham-Louis Breguet. Before the development of this piece, François-Paul had a discussion with a collector friend of his who asked him, if he were to make himself any watch, what would he make? His response was that he would make something that appeared very simple on the surface, but had vast complexity beneath. He added that it would likely be a time-only piece, and that it would have a Remontoire D’Egalité or ‘dead beat seconds’ with a very special escapement. The patented design utilises its Remontoire to average the force-delivery from the twin-barrel mainspring, thus giving the escapement a far superior regulation.

 

While understanding the concepts of the more complex escapements may elude some, we hope that the basic principles of the escapement are now a little clearer. 



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