Key components of a mechanical watch movement

Last Updated on May 19, 2024 by Jason

The movements in vintage watches are typically mechanical, although it is entirely possible for a vintage era watch to include a quartz movement. Most of the vintage watches that will appear on this website will have mechanical movements, hand-winding or automatic. Although, you have probably spent a lot of time admiring that vintage watch on your wrist, have you ever wondered what is going on inside? In this introductory post, we will explore the inner workings of a mechanical movement by looking at the key components. Hopefully, this will give you a better understanding of how your vintage watch works.

This is by no means a comprehensive list, covering every aspect of every available movement. Each movement will be slightly different when it comes to components and arrangement. However, this guide will certainly provide you with a solid understanding of the key components.

Crown assembly

Visible from the exterior, the crown is generally the only point of contact between the wearer and the watch movement. The wearer will use the crown to wind the watch and to set the time. To aid grip, the crown typically features a grooved or ribbed exterior (hence its name). The end of the crown is quite often embossed with the brand’s logo. The crown is connected to the winding stem and can be pulled out to varying lengths to access different settings. This clicks the setting lever into different slots on the setting jumper as the crown moves back and forth. The crown mechanism is connected to the motion works to enable features such as time adjustment.

Most watches also feature a hand-winding capability, allowing the user to rotate the crown (at a set length) to manually tighten the mainspring and provide power to the movement. This is generally available in both hand-winding and automatic movements.

Mainspring

The mainspring is a thin, 20-30cm long strip of hardened metal, coiled to form a spring structure. The mainspring is the power source for the movement in both hand-wound and automatic watches. This metallic spring is housed within the toothed mainspring barrel, to prevent it from unravelling. In the centre sits the winding pinion, attached to a ratchet wheel and click assembly that sits below. This ensures the pinion can only rotate in one direction, preventing the mainspring from unwinding. Thanks to the ratchet and clicker, all momentum from the mainspring is released via the mainspring barrel.

Gear train

Positioned next to the mainspring, the gear train is a series of interlocking gears that drive the timekeeping hands and other wheels within the movement. The centre wheel is driven directly by the mainspring barrel, rotating fully once per hour. This powers the minute hand of the watch. The motion works, which follows next, drives the hour hand.

The third wheel adjoins the centre wheel to the fourth wheel, which rotates once per minute. This powers the second hand when present. Each gear runs from a central axle featuring a synthetic jewel bearing, to massively reduce friction and wear over time. The gear train is also known as the drive train or wheel train.

Motion works

The motion works is a special set of gears, positioned next to the centre wheel, which help provide additional functionality. Firstly, these allow the watch hands to be independently rotated for time setting. Additionally, they perform a speed reduction at a ratio of 12: to 1 for the hour hand. This essentially makes the hour hand run 12 times slower than the minute hand, despite both hands sharing the same axle. The gears involved with this speed reduction are the cannon pinion, the minute wheel and hour wheel.

The escapement

The timekeeping component of the watch is the escapement, without it, the mainspring would unwind in seconds. The escapement assembly is easily visible in most mechanical wristwatches and is usually the most obvious moving component. The lever escapement is the most common type.

Positioned at the end of the gear train, the escapement is the most fragile part of any vintage watch movement. The escapement controls the release of power from the mainspring. Force is transferred from the mainspring to the escape wheel via the gear train. The rotation of the escape wheel pushes against the pallet fork, which in turn nudges a section of the balance wheel. The rotation of the balance wheel is kept in check by the hairspring, which contracts to oscillate the wheel back towards the pallet fork.

As the balance wheel returns, it clicks the pallet fork into a second position, releasing the escape wheel for a brief moment before holding it in place once more with the other fork prong. This process restricts the movement of the escape wheel to a very short distance, rather than allowing it, and the other gears, to spin freely. This process repeats itself several times a second and generates the ticking noise in the watch. The frequency of this process is also what determines the beat-rate of the watch, indicating how many times the second hand moves each second. The ticking is very fast, occurring perhaps 5 times per second. It happens so quickly that it creates the illusion that the second hand is actually “sweeping”.

The escapement assembly not only uses jewels to minimise friction and wear, but also generally houses a shock protection mechanism, such as Incabloc or Kif. This is to prevent it from being damaged if the watch is impacted by a sudden shock.

Individual mechanical watch components

Balance wheel – A hollow rotor-like structure that forms part of the escapement assembly. In combination with the hairspring, it oscillates back and forth to help direct the pallet fork into the correct position.

Complications – Additional features, beyond timekeeping, that can be added to a watch to give more information to the wearer. Common complications include date, day and chronograph (stopwatch).

Escape wheel – An unusually shaped gear that receives momentum from the mainspring and combines with the balance wheel, hairspring and pallet fork to create the escapement assembly. Combined, these components regulate the timing of the movement.

Hairspring – A small, thin strip of coiled metal attached to the balance wheel. This expands and contracts, allowing the balance wheel to oscillate and return to the pallet fork.

Jewel bearings – Small pieces of synthetic gem, usually ruby or sapphire used to reduce friction on key components within a mechanical movement. Generally, the more jewels, the higher the quality of the movement. Jewels increase the lifespan of the bearings, resulting in lower servicing costs over time.

Rotor – Automatic wristwatches feature what is known as a ‘rotor’. This is a weight, typically crescent-shaped, that sits at the base of the movement. The rotor moves freely as the watch is rotated on the wearer’s wrist. The movement of the rotor rotates the central staff, which is attached to the winding mechanism. This movement automatically self-winds the watch, without the need for the user to rotate the crown.

Setting jumper & lever – These two components combine to form a mechanism that requires the crown to be pulled out before manipulation. This not only allows for multiple functions, but also prevents accidental adjustments to the time. The vast majority of vintage wristwatches utilise a lever-set mechanism in this way.

Spring barrel – The mainspring housing, typically featuring a toothed outer, akin to a traditional gear. This barrel will typically pair with a cover, to prevent the mainspring ejecting from its container.

Plates – A variety of specially shaped metal plates that provide a framework to hold the components of the movement in place. The largest ‘main’ plate acts as a base, while the second-largest plate known as the ‘barrel bridge’ holds the mainspring with its associated components. There are smaller sections, including the ‘gear bridge’ which supports the gear train arrangement. The pallet bridge which holds the pallet fork and the balance bridge above, which supports the balance wheel and the remaining regulator assembly.

Winding stem – A rod attached to the crown that transfers the crown inputs to the mechanisms within the movement. One end is threaded and cut to size depending on the case dimensions, to fit the crown. The other is square, which interlocks with the winding and setting mechanisms; varying depending on the movement used.

Winding pinion – The winding pinion is a toothed wheel, akin to a gear, that forms part of the mainspring assembly.

Yoke & sliding pinion – Two further components of the crown arrangement, which work together with the setting jumper, to ensure the correct functions are enabled when the crown is extended to a specific length. When the setting jumper is engaged, the spring-loaded yoke moves the sliding pinion to engage with specific gears, most notably the motion works.