The Great (Clock) Escapement

In mechanical watches and clocks, an escapement is a device which converts continuous rotational motion into an oscillating or back and forth motion, creating the familiar ticking noise. [Wikipedia.org definition of 'Escapement']

Just as human bodies rely on the heart to regulate overall function, some clocks and watches depend on their escapements for proper overall function. In the world of horology the escapement is a mechanism which is composed of a wheel and anchor, used to regulate periodic impulses with a pendulum or by a balance effect. Without the escapement, the clock wouldn’t work properly. Of course the “heart” of most modern clocks or watches today is the battery or electrical cord, which sends power to the popular device that replaced escapements: a resonator resembling a tuning fork, using quartz crystals and vibrations as regulation. While escapements are not nearly as popular today as they once were, they are still used in several time-keeping pieces.

Escapements are commonly used today in many decorative clocks. Tall stand-alone grandfather clocks, wall clocks with a pendulum and cuckoo clocks are all time-telling devices that often are still driven by an escapement. In the world of watches, the mechanical watch also uses an escapement today. These eye-catching wrist or pocket timepieces are intended mostly to flaunt or to match a person’s unique style since they are not extremely reliable with time-keeping. Even today escapement-driven timepieces are what most people would refer to as “temperamental,” meaning they inconsistently wind too slow or too fast; models requiring winding will stop altogether if they are not wound regularly. Since some escapements rely on gravity also, they tend to function differently at various altitudes.

To better understand the escapement mechanism and exactly how it works, the history of this fascinating component and its evolution should be understood, beginning with the most simple version. Around the late 1200s, the first escapement was crafted, functioning by way of a bar called a foliot with a weight on each end. Another vertical bar called a verge has a plate at the top and one at the bottom on either side. Each plate takes turns pushing the foliot, alternating in the escape wheel’s path; the motion and force keep the action repeating. Because it has no exact regulation, the time shown on a clock with this escapement would be far from being reliably accurate.

Robert Hooke introduced the anchor escapement in 1660. This was the beginning point of some form of consistency. Although it was still not completely reliable, it was seen as a great improvement. This type of escapement is made of a jagged wheel with a back-and-forth moving anchor above it, which is connected to a pendulum. Plates on the anchor then alternately catch onto the jagged wheel, causing the regulated movement.

The lever escapement was a common type of device used in watches for centuries. This type of escapement uses two separate wheels – a large wheel and a small wheel below it. Actually the smaller wheel is a round gear used to regulate the larger wheel, which has a bar across it. The movement is a back-and-forth motion regulated by an effect similar to a see-saw. While one side of the bar on the wheel moves up, the smaller gear wheel turns until the other side raises, as the first side lowers.

In 1748 another famous escapement in history was invented by Pierre Le Roy: the detent escapement. Modified and utilized by several others in the future, this type of escapement was used in a few select precision watches and Marine chronometers. The detent is a detached escapement similar to the lever escapement with its separate wheel and also has a self-starting feature. Slightly an improvement over the lever escapement, the detent has less friction between the plate and escape tooth, making its accuracy improved in comparison with the lever escapement. The detent escapement was used through the mid-1900s before it was replaced.

Beginning in the late 1700s and lasting nearly a century, the popularity of duplex escapements increased. These frictional rest escapements are powered by a balance wheel receiving impulses. The escape wheel has two jagged teeth, with additional ones on the wheel sticking upward and outward. As one tooth leans against a disk, the wheel moves into the center, causing the tooth to be freed from the disk. The teeth then alternate on a roller as the process continues. As the wheel turns clockwise, the impulse tooth pauses on the roller without being released.

In the 18th century, the gravity escapement gained popularity, using a weight or spring to send an impulse to the pendulum. There are two angle-planed arms, one each holding a deadbeat pallet. As one arm raises, a toothed escape wheel is released. One of the teeth then moves upward on the other arm’s angle face, causing the arm to raise. During this time the other arm drops to a lower level, sending an impulse directly to the pendulum.

More recently in the 1970s and 1980s, the co-axial escapement came into the picture and gained popularity. George Daniels is credited with inventing this escapement which functions in a similar fashion to the lever and detent designs. The impulse is separated from the locking function by way of 3 pallets. Much more complex and intricate than its predecessors, the co-axial escapement does not experience sliding friction. Since friction is what causes the most wear and damage on escapement gears, this was Daniels’ main focus in crafting. At this point in history the quartz-powered clocks and watches had taken over, so escapement-driven clocks and watches were intended as novelties or sophisticated wrist and pocket decorations and not so much as a timepiece to depend upon for precise time-telling.

Escapement-driven clocks and watches are fascinating pieces to take the back panel off of and study.

Most people don’t realize all the intricate processes taking place behind the face of a pendulum clock or mechanical watch.

Certainly these clocks are not as accurate as those that are relied upon to know the exact time, but for any timepiece enthusiast these treasures are worth every cent for their amazing mechanical structure or nostalgic value.

Tags: anchor escapement, clocks, co-axial escapement, detent escapement, duplex escapement, escapement, escapement mechanism, escapements, foliot, gravity escapement, horology, lever escapement

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