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How to take apart a watch or clock and study its internal mechanisms – a HowTo guide and introduction to the fascinating world of Horology.

Cutaway drawing of a pocketwatch movement

Watches and clocks incorporate everything geeks love – complexity, style, engineering, math and more. They are fascinating devices to examine. If you’re a collector or just curious about how watches and clocks work, you may want to disassemble (check out this 149-piece toolkit!) and inspect the internal mechanisms of a watch. And with modern-day digital cameras at hand to record their complex inner workings, horology is much easier than it was in the past. Here are the steps to follow to disassemble and examine the inner workings of a watch or clock.

Horology – the study of time

Horology is the study of time or more accurately, the measurement of time. Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time. In current usage, horology refers mainly to the study of these mechanical time-keeping devices and horologists are the people who study them.

Step 1: Gather the necessary tools

Before beginning the disassembly of your watch, it is important to gather the necessary tools. You will at a minimum, need a set of precision screwdrivers, a pair of tweezers, a magnifying glass, and a soft cloth or pad to work on. These tools will enable you to safely and effectively take apart the watch. Common watchmaker tools include:

  1. Screwdrivers: Watchmakers use screwdrivers of various sizes to remove and tighten screws in the watch movement and case.
  2. Tweezers: Watchmakers use tweezers to handle small parts and components that require precise placement.
  3. Loupe: A loupe is a small magnifying glass that allows watchmakers to inspect and examine small parts and components.
  4. Pliers: Watchmakers use pliers to hold and manipulate parts that are too small or delicate to handle with their fingers.
  5. Hand Remover: A hand remover is a specialized tool that is used to remove the watch hands without damaging the delicate movement.
  6. Case Opener: A case opener is used to open the watch case back, allowing watchmakers to access the movement and make repairs.
  7. Movement Holder: A movement holder is used to securely hold the watch movement while the watchmaker works on it.
  8. Oil Cups: Watchmakers use oil cups to hold small amounts of lubricating oil for precision application.
  9. Spring Bar Tool: A spring bar tool is used to remove and replace the spring bars that hold the watch band in place.

Step 2: Remove the back cover

Once you have the necessary tools, the first step is to remove the back cover of the watch. Use a flathead screwdriver or specialized case opener to carefully remove the back cover. If the watch has a hinge, be sure to open it gently to avoid damaging it.

Step 3: Locate the stem and crown

The stem and crown are responsible for setting the time and winding the watch. Carefully remove them by unscrewing the screws that hold them in place. It is important to keep track of these screws and their location.

Step 4: Remove the movement

The movement is the heart of the watch and includes the balance wheel, mainspring, and escapement. Use your tweezers to gently remove the movement from the case.

Step 5: Disassemble the movement

Using your precision screwdrivers, remove the screws that hold the movement together. Be sure to keep track of each screw and its location as you remove them. Periodically snapping pictures with your cellphone helps greatly. Also, it is important to work in a clean and well-lit area to prevent losing any small parts.

What is a watch movement?

A watch movement is the mechanism that powers the watch and enables it to keep time. There are three main types of watch movements: mechanical movements, quartz movements, and automatic movements. Each type of movement has its own advantages and disadvantages, and the choice of movement will depend on the individual’s preferences and needs.

1. Mechanical Movements

Mechanical movements are the oldest type of watch movement and are still used today in high-end watches. These movements use a spring to store energy, which is then released at a constant rate to power the watch. Mechanical movements are generally more accurate than other types of movements, but they require regular maintenance and can be quite expensive. Mechanical watches also have a sweeping second hand movement that is smoother and more fluid than the ticking movement of quartz watches.

2. Quartz Movements

Quartz movements are the most common type of watch movement and are used in most modern watches. These movements use a small battery to power a quartz crystal, which vibrates at a precise frequency to keep time. Quartz movements are very accurate and require little maintenance, but they are generally less expensive than mechanical movements. Quartz watches are also known for their accuracy and reliability, and they are often used in sports and outdoor activities.

3. Automatic Movements

Automatic movements, also known as self-winding movements, are similar to mechanical movements but do not require manual winding. These movements use a rotor that moves with the motion of the wearer’s wrist to wind the watch automatically. Automatic movements are more expensive than quartz movements, but they are also more accurate and require less maintenance than mechanical movements. Automatic watches are popular among watch enthusiasts and collectors because of their mechanical complexity and traditional craftsmanship.

In summary, each type of watch movement has its own unique features and benefits. Mechanical movements offer precision and craftsmanship, while quartz movements offer accuracy and affordability. Automatic movements provide the best of both worlds, with accuracy and low maintenance combined with traditional craftsmanship. The choice of watch movement ultimately depends on the individual’s preferences, needs, and budget.

The watch movement in depth

There are five parts in all mechanical watches that comprise the watch’s movement:

  1. A mainspring which stores energy and powers the watch.
  2. A gear train which sends the energy from the mainspring to the balance wheel and measures the passing of time in seconds, minutes, and hours. The gear train has a part called the “keyless work” that lets you wind the mainspring and move the hands to set the time.
  3. A balance wheel that swings back and forth and keeps time. It’s accurate because it swings at a constant rate.
  4. An escapement mechanism that gives the balance wheel a push to keep it swinging and moves the watch’s gears by a set amount with each swing. This makes the “ticking” sound of the watch.
  5. An indicating dial, usually a clock face, to show the time.

Watch mainspring

The mainspring, which is a spiral ribbon of spring steel, is inside a barrel with gear teeth that turn the center wheel once per hour. On the other side of the watch face, the cannon pinion is attached to the minute hand and drives the hour wheel.

The duration of run, or how long a mechanical watch can run without being wound, depends on the size of the mainspring and how much power is needed. If the watch is dirty or worn, the energy may not transfer efficiently to the escapement, making the watch run slow. Most mechanical watches run for 36 to 72 hours. Some can run for a week. The exact duration of run for a mechanical movement is calculated with the formula

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where z1 is the number of barrel teeth, z2 is the number of center pinion leaves, n1 is the number of revolutions of the barrel, and n2 is the number of revolutions of the center pinion — the run duration.

Gear train

The gear train is a series of gears that transmit power from the mainspring to the hands of the watch. The gear train includes the center wheel, the third wheel, the fourth wheel, and the escape wheel. The center wheel receives the power from the mainspring and transmits it to the third wheel. The third wheel turns the fourth wheel, which is connected to the minute hand. The escape wheel, which is connected to the balance wheel, controls the release of power from the gear train.

Escapement

The escapement wheel is a fundamental component of a mechanical clock. It regulates the movement of the clock’s hands. It consists of a series of teeth on a gear that interacts with the pallet fork, a lever that rocks back and forth. The escapement wheel’s purpose is to maintain the accuracy of the clock by controlling the rate at which the mainspring’s energy is released.

When the clock’s mainspring unwinds, it transfers its energy to the gear train, which rotates the escapement wheel. The pallet fork engages with the teeth on the escapement wheel, which causes the fork to rock back and forth. The pallet fork rocks back and forth in such a way that it allows the gear train to move forward by one tooth with each movement of the pallet fork. This process is what makes the clock tick.

The pallet fork’s movement is regulated by the clock’s balance wheel, which controls the rate at which the escapement wheel rotates. The balance wheel is a weighted wheel that oscillates back and forth, and its speed is controlled by a hairspring. The hairspring ensures that the balance wheel oscillates at a constant rate, which in turn regulates the movement of the escapement wheel. The balance wheel’s regulation of the escapement wheel’s movement is what sets the clock’s accuracy.

As the escapement wheel rotates, it advances the clock’s hands by a fixed amount. The pallet fork engages with the teeth on the escapement wheel, and then disengages, allowing the wheel to rotate slightly before engaging again. This process repeats, causing the clock’s hands to move forward in a smooth, steady motion.

Balance wheel and hairspring

The balance wheel is what makes the watch keep time. It has a heavy wheel that moves back and forth, and a spring called the balance spring or “hair spring” that pulls it back to the middle. Together, the wheel and spring make a “harmonic oscillator.” The weight of the wheel and how stiff the spring is work together to control how long each swing of the wheel takes. A balance wheel’s period of oscillation T in seconds, the time required for one complete cycle (two beats), is

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where I is the wheel’s moment of inertia in kilogram-meter2 and k is the stiffness (spring constant) of its balance spring in newton-meters per radian. Most watch balance wheels oscillate at 5, 6, 8, or 10 beats per second. This translates into 2.5, 3, 4, and 5 Hz respectively, or 18000, 21,600, 28,800, and 36,000 beats per hour (BPH).

The hairspring works with the balance wheel, which is a weighted wheel that oscillates back and forth. As the balance wheel oscillates, the hairspring contracts and expands, providing a restoring force that keeps the balance wheel moving at a consistent rate. The length and thickness of the hairspring determine the rate at which the balance wheel oscillates, and therefore, the rate of the clock. If the hairspring is too long or too thick, it will slow down the clock, and if it is too short or too thin, it will speed up the clock.

In most watches there is a regulator lever on the balance spring which is used to adjust the rate of the watch. It has two curb pins which embrace the last turn of the spring, holding the part behind the pins motionless, so the position of the curb pins determines the length of the spring. Moving the regulator lever slides the curb pins up or down the spring to control its effective length. Sliding the pins up the spring, shortening the spring’s length, makes it stiffer, increasing k in the equation above, decreasing the wheel’s period T so it swings back and forth faster, causing the watch to run faster.

Keyless work (a special set of inner gears)

A special set of gears called the keyless work winds up the mainspring when the crown is rotated. When the crown is pulled out a little, it allows the hands to be moved to set the watch. The stem attached to the crown has a gear called the clutch or castle wheel, which has two rings of teeth on either end. When the stem is pushed in, the outer teeth turn the ratchet wheel on top of the mainspring barrel, which turns the shaft that the inner end of the mainspring is attached to, winding the mainspring tighter around the shaft. A spring-loaded pawl or click presses against the ratchet teeth, stopping the mainspring from unwinding. When the stem is pulled out, the inner teeth of the castle wheel engage with a gear that turns the minute wheel. When the crown is turned, the friction coupling of the cannon pinion allows the hands to be rotated.

Center seconds

If the seconds hand is pivoted at the center of the dial, it’s called “center seconds” or “sweep seconds” because it sweeps around the minute track on the dial. In the past, center seconds hands were driven off the third wheel, sometimes via an intermediate wheel, with the gearing on the outside of the top plate. This is called indirect center seconds. Because the gearing was outside the plates, it added to the thickness of the movement, and because the rotation of the third wheel had to be geared up to turn the seconds hand once a minute, the seconds hand had a fluttering motion.

In 1948, Zenith introduced a watch with a redesigned gear train where the fourth wheel was at the center of the movement, and so could drive a center seconds hand directly. The minute wheel, which had previously been at the center of the movement, was moved off center and drove the minute hand indirectly. Any fluttering due to the indirect gearing is concealed by the relatively slow movement of the minute hand. This redesign brought all the train gearing between the plates and allowed a thinner movement.

The use of jewels in watches

Jewel bearings were created to reduce friction in watches. They were first introduced by Nicolas Fatio de Duillier and Pierre and Jacob Debaufre around 1702. They were not widely used until the mid-19th century. Until the 20th century, they were made from small pieces of natural gems, such as garnet, quartz, and glass. Only top-quality watches used sapphire or ruby. In 1902, a process to grow artificial sapphire crystals was invented, making jewels much cheaper. Today, jewels in modern watches are all synthetic sapphire or ruby, made of corundum, one of the hardest substances known. The only difference between sapphire and ruby is the color. There is no difference in their properties as a bearing. Using jewels is advantageous because their ultrahard slick surface has a lower coefficient of friction with metal. The static coefficient of friction of steel-on-steel is 0.58, while that of sapphire-on-steel is 0.10-0.15.

How to disassemble a watch movement

Disassembling a watch movement can be a challenging task, but with patience, careful steps, and attention to detail, you can do it successfully. If you want to clean or repair your watch, you need to know how to take it apart without causing any damage. Here are the steps to follow:

  1. Start by removing the balance wheel and hairspring. These are the vital components that regulate the movement of the watch. You need to be very careful when removing them so that you don’t damage them. It’s important to note that the hairspring is fragile and delicate, so you should avoid touching it as much as possible.
  2. Remove the pallet fork and escape wheel. These components work together to control the release of energy from the mainspring. You should be extra cautious when removing the pallet fork as it’s a delicate component that can easily be bent or damaged.
  3. Keep each part in a separate container to avoid mixing them up. This is essential because each component is unique and has a specific role in the movement. If you mix them up, you might have difficulty putting them back together, which can cause problems down the line.
  4. Remove the center wheel and barrel bridge. These components are responsible for transferring power from the mainspring to the rest of the movement. They’re usually located at the center of the movement, and you’ll need to remove them before you can disassemble the rest of the watch.
  5. Remove the crown wheel and ratchet wheel. These components work together to wind the mainspring and are essential for the watch’s operation. You need to be careful when removing them so that you don’t damage the teeth or the pivot points.
  6. Finally, remove the winding stem and set lever. These components allow you to adjust the time on your watch. You should be gentle when removing them so that you don’t damage the threads or the keyless works.

Step 6: Inspect the parts

At this point, a watchmaker will carefully inspect the watch’s parts for damage, wear, or dirt. Use your magnifying glass to get a closer look at each component. You may notice some parts that need to be replaced or repaired.

Step 7: Clean the parts

Once the parts have been carefully inspected, a watchmaker will clean the watch components to ensure smooth, accurate operation of the timepiece. Using a soft cloth or pad, gently clean each part. Avoid using water or harsh chemicals as these can damage the delicate parts of the pocket watch. It is best to use a specialized cleaning solution made for pocket watches.

Step 8: Reassemble the movement

Carefully reassemble the movement in the reverse order of disassembly, making sure to replace each screw in its correct location. Be sure to handle the parts with care and avoid overtightening the screws.

Step 9: Reinsert the movement

Gently place the movement back into the pocket watch case, ensuring that it fits snugly. It is important to make sure that the movement is properly aligned and seated.

Step 10: Reattach the stem and crown

Screw the stem and crown back into place, being careful not to overtighten them. It is important to make sure that the stem and crown are properly aligned and seated.

Step 11: Replace the back cover

Finally, replace the back cover of the pocket watch, being sure to reattach any hinges if necessary. It is important to make sure that the back cover is properly aligned and seated.

Following these steps should allow you to successfully disassemble and reassemble a pocket watch while gaining insight into its inner workings. Remember to work carefully and patiently, as pocket watches are delicate and intricate devices. With the right tools and techniques, taking apart a pocket watch can be an enjoyable and rewarding process.

You can read a complete Watchmaking ebook here.

Image Credits

In-Article Image Credits

Clocks: a watch-maker seated at his workbench with a long-case and a bracket clock behind him, diagrams of movements above his head via Wikimedia Commons by This file comes from Wellcome Images, a website operated by Wellcome Trust, a global charitable foundation based in the United Kingdom with usage type - Creative Commons License
Cutaway drawing of a pocketwatch movement via Wikimedia Commons by B. G. Seielstad with usage type - Public Domain. December 1931

Featured Image Credit

Cutaway drawing of a pocketwatch movement via Wikimedia Commons by B. G. Seielstad with usage type - Public Domain. December 1931

 

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