How Pocket Watches Work

Pocket watches have been made since the 16th century; their popularity as portable timepieces ebbed with the introduction of wristwatches around the beginning of the 20th century, but pocket watches are still being manufactured, and vintage models remain popular with collectors around the world. Their construction has evolved over the centuries.

There are two main kinds of pocket watch. An open-faced watch, or lépine watch, lacks a metal cover to protect the dial. The pendant is normally located at twelve o’olock, and the sub-second dial at six o’clock. Hunter-cased watches, on the other hand, have spring-hinged circular metal rims or covers that close over the dial, protecting them from dust and scratches. Most vintage hunter-cased watches are hinged at the nine o’clock position.

Likewise, there are different kinds of watch movements. The earliest pocket watches, and most watches produced until the latter half of the 19th century, had key-wind and key-set movements. According to this system, a watch key was required to wind the watch as well as set the time. This was usually done by opening the caseback and applying the key over the winding arbor.

Stem-wind and stem-set movements were first developed in the 1850s; these remain the most common pocket watch movements. These watches are wound and set using a stem. Stem-wind, lever-set movements, on the other hand, are required for railroad watches -- watches that meet rigid specifications required for railroad workers. These watches are wound with a stem, but must be set by opening the crystal and bezel and pulling out a setting-lever. Once the lever is pulled out, it can be turned to set the proper time. This kind of setting device makes it nearly impossible to accidently change the time on a watch.

Also, some movements have stem-wind, pin-set functions. The watches are wound by stem, but are set by pressing down on a small pin and then turning the crown.

Quality pocket watches are always “jeweled”: the jewel is a small, crafted piece of a hard mineral, and jewels are placed in various places in the watch movement to help reduce friction. Jewels used in vintage watches are usually rubies, sapphires, garnets, and diamonds; beginning in the 20th century, most watch jewels were synthetic. The jewels themselves have little value, but a jeweled pocket watch, because it is more finely crafted and is better quality, has more value in most cases than a similar nonjeweled watch.

There are several types of jewels used in pocket watch movements. The most common are hole jewels, which are donut-shaped jewels that fit over gear axles (or “wheel arbors”); cap jewels, which are flat jewels that are positioned over the ends of the axles; pallet jewels, which are brick-shaped jewels that are positioned to alternately engage and release the escape wheel; and roller jewels, which are positioned on the large balance wheel that swings back and forth, to engage with the pallet fork. Most jeweled watches have a minimum of seven basic jewels, but some may have as many as twenty-three jewels.

Most pocket watches have five primary mechanical components: a mainspring, a gear train, a balance wheel, an escapement mechanism, and a clock face. The primary action of a pocket watch is that the mainspring becomes compressed when the watch is wound; this stored-up mechanical energy is used to power the watch.

The mainspring, as it releases mechanical energy, is attached to a cylindrical barrel with gear teeth. These gear teeth turn the gear train, which consists of four separate wheels attached to one another with their own sets of gear teeth. The barrel is directly attached to the center wheel, which in turn is attached to the escapement mechanism.

The escapement mechanism is basically a pendulum that rocks back and forth with each rotation of the center wheel. One end of the escapement mechanism is attached to an upright pin on the balance wheel. The movement of the escapement mechanism causes the balance wheel to advance in regular intervals, thereby allowing the watch to keep time. Attached to the balance wheel is a cannon pinion that attaches to the minute wheel. The cannon pinion also drives a gear reduction mechanism that rotates the hour wheel one time for every twelve rotations of the minute hand. Both the hour and minute wheels contain shafts going through the clock face and attaching to the watch hands.

The mechanics of a pocket watch are not complicated, but achieving great precision with such miniaturized mechanical components takes extraordinary skill.

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