The Easiest Guide to Coaxial Escapement

One thing we know about the universe is that it’s infinitely complicated. And one thing about coaxial escapements – they’re pretty darn complicated too (keep reading if you don’t find this metaphor one bit self-aggrandizing). 

 

Before getting into it, we need to remind ourselves that an escapement in mechanical watches is, essentially, a linkage that gives an impulse to the timekeeping element and releases the gear train forward, mimicking a pendulum. We will also need to define a few key terms: lever escapement and detent escapement. 

Lever Escapement

Here, the escape wheel, powered by the mainspring, is connected to the watch's wheel train. Its rotation is controlled by the pallets attached to the lever. The escape wheel has special teeth that interact with the entrance and exit pallets, typically having 15 teeth. The fork at the end of the lever receives an impulse from the balance roller via an impulse pin. This unlocks the entrance pallet, allowing the wheel to rotate clockwise. As it rotates, the entrance tooth slides across the entrance pallet, turning the pallets and placing the exit pallet in its path. Once the exit tooth lands on the locking face of the exit pallet, the escape wheel is locked in place. In this process, the escape wheel turns one half of its total rotation angle of 24 degrees. As the tooth moves over the impulse face, it transfers energy to the balance wheel via a ruby impulse pin. The wheel is held in place by the exit pallet jewel and must be turned back slightly in order to unlock it. Once released, the balance wheel rotates freely until pulled back by the hairspring. This cycle repeats at a rate of 18,000 beats per hour, with two impulses per cycle.

The lever escapement is strong and reliable, providing a consistent energy boost to the balance. It also allows for both directions of swing. A major plus is that it's self-starting, no jiggling required. One downside is the scraping between the escape wheel and pallet, which creates friction and requires regular oiling to prevent wear and energy loss. Over time, this can affect precision. 

Detent Escapement

The detent escapement uses a thin metal spring with a jewel attached to hold the escape wheel in place. When the balance swings by, it trips the spring and releases the escape wheel, which then powers the balance directly. This design is efficient and doesn't need oil, but it can be easily tripped by shock and cannot start on its own. It was mostly used for marine chronometers and some high-precision pocket watches. John Arnold is credited as its inventor in 1775. 

Coaxial Escapement

Now, this brings us to the coaxial escapement. When the quartz crisis hit, American watch collector Seth G. Atwood hired English watchmaker George Daniels to make a watch that would revolutionize mechanical timepieces. This led to Daniels creating and patenting the coaxial escapement in 1974 and 1980, respectively.

The coaxial escapement is a modern version of the lever escapement, combining elements from the detent escapement. It uses three pallets to separate the locking and impulse functions, reducing friction and eliminating the need for constant lubrication. However, a small amount of lubricant is still used on certain parts to prevent damage. The main advantage of the Daniels escapement is that it greatly reduces sliding friction. This means less wear and tear on the parts and better accuracy in timekeeping.