Kevin Lowey | Watches | How Your Watch Works

As Time Goes By

 

What Makes your Watch Tick

Introduction

This document gives a brief introduction to how pocket watches work, then refers you to more detailed sources of information on this topic.

A pocket watch consists of the following basic components:

  • A mainspring to provide the power
  • A set of gears to drive the hour, minute, and second hands
  • A regulating mechanism to keep the speed of the gears constant.

The Mainspring

The mainspring is the engine of the watch. This is a strong spring that is wound tight using either a key (in older watches), or a ratchet built into the crown of the watch. As the spring unwinds, it runs the gears and other mechanical components of the watch (like special animations, chimes, etc.). The spring usually has enough power for 1.5 to 2 days.

Mainsprings can break from overwinding, or if the watch is dropped. Often there is a "safety pinion" built into the spring mechanism to protect the rest of the watch if the mainspring breaks. A mainspring is less likely to be damaged if it is wound up, so you should always wind your watch before shipping it someplace or doing anything else that could accidentally jolt it.

The Gears or "Going Train"

The mainspring drives the watch's "Going Train". Usually this consists of five gears. The gears are designed to move the hour, minute, and second hands at the right number of revolutions relative to each other. (60 seconds in a minute, 60 minutes in an hour, etc.) Watches with built-in calendars may have a more complicated gearing system.

Attached to the gearing system is a "clutch" that allows you to bypass the mainspring and turn the gears by hand so you can set the time. Some old timepieces use a special key for this. In others, you must pull out a lever to engage the "clutch" so the hands move freely. Most of us are familiar with newer watches, where you pull out the crown to disengage the mainspring and enable you to set the watch.

Gears can cause a lot of friction as they spin in their mountings. Over time, this can loosen the gears so they don't work properly. Watchmakers prevented this by using gemstones at key friction points to reduce the wear. A watch with more of these "jewels" is usually of higher quality as it wears out slower.

Regulating Time, the Lever Escapement

If left unchecked, the powerful mainspring of the watch would make the hands spin out of control. They would go fast at first, then slow down until they finally stopped as the mainspring unwound. A method was needed to slow down the unwinding of the mainspring to a constant speed.

The Lever Escapement solved the problem. It serves the same function as a pendulum on a clock, without using a pendulum. Instead, a small two-headed lever called an "escapement" interacts with the "escape wheel" (the last and fastest moving gear in your watch). The escape wheel gives the lever a little push. This, in turn, pushes a "balance" in one direction. Pushing back against the balance is a hair-thin "balance spring". The tension in this spring is enough to stop the balance, and push it back against the lever again. This in turn moves the lever, allowing the escape wheel to move one more "click" ahead. Instead of a pendulum moving back and forth, we have the balance and balance spring moving back and forth.

The lever moves back and forth 4 to 5 times per second, hitting the teeth of the escape wheel. This is what makes your watch tick. The design of the parts in this system contributes greatly to the accuracy of your watch.

Other Resources

Here's some other places to look for more information, diagrams, etc. on how a watch works.


Copyright 1998-2001 Kevin Lowey
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