Gear Train Explained

In a mechanical watch, the mainspring provides power and the balance/escapement control it, but what carries that power throughout the movement? A specific set of gears known as the gear train manages power and controls the hands, and although not interchangeable between different movements, the arrangements are generally the same. The gear trains in clocks tend to vary a bit, but watches are surprisingly standard and have the same parts overall. They’re made up of wheels (large gears) and pinions (smaller gears) that mesh together, and arbors are the shafts that hold them. Think of it (loosely) as the transmission of the watch.

Going Train

Time-only watches need one primary gear train, but more complex movements with multiple complications have other gear trains to tie everything together. To keep things simple, we’ll focus on the principal one that transfers power from the barrel to the balance and escapement, known as the going train. The mainspring must unwind very slowly or the power reserve will be short, so the going train speeds things up as power is transferred, again like a transmission. Specific gears also have precise ratios that turn the minutes, hours and seconds, ultimately based on the frequency (Hz) of the balance wheel. These gears are under constant load from the mainspring, so the arbors are almost always connected to jewel bearings to reduce friction and wear.

A Common Layout

The vast majority of going trains have the same general layout - the first wheel, second wheel, third wheel, fourth wheel and finally the escape wheel. Makes sense, right?

The first wheel is attached to the mainspring barrel and a ratchet allows the watch to be wound without the wheel turning. This meshes with a pinion connected to the second wheel and is the first contact between the mainspring and gear train.

The second wheel turns once per hour and consequently connects to the minute hand via an arbor through the dial. It also meshes with the third wheel’s pinion. If a watch has a central seconds hand, the second wheel is off-center to make room for the fourth wheel that drives the seconds hand. The second wheel is sometimes referred to as the center wheel as it’s often positioned in the center (if there’s not a central seconds hand), but for simplicity we’ll stick with “second wheel.” To make things more complicated, the second wheel also drives the hour hand via a 12:1 reduction gear train, known as the motion work.

The third wheel is an intermediary, turned by the second wheel and driver of the fourth wheel’s pinion. As the name suggests, it’s the third wheel in the going train.

The fourth wheel turns once per minute and moves the seconds hand on the dial, while also meshing with the pinion on the escape wheel. If the watch has a tourbillon like Horage’s Tourbillon 1 and Lensman 1, the fourth wheel both rotates the cage and powers the balance/escapement. Clock movements can often eliminate the fourth wheel as their escapements are slower than watches, allowing the third wheel to connect directly to the escape wheel.

The escape wheel is the end of the line and creates controlled impulses by engaging with the pallet fork, one tooth at a time. This occurs via each swing of the balance (or pendulum in a clock) and controls the mainspring’s power release. Without it, power would quickly drain like a windup toy.

Other Gears

There are, of course, other gears in a movement that are vital to its operation. Winding a modern watch requires keyless works, which are a series of gears that start on the crown stem. They also set the time when the crown is pulled out. Adrien Philippe invented this in 1843 and it remains the standard today. Prior to keyless works, a watch was wound and set via a separate key inserted in the back. The clutch is the gear attached to the crown’s stem and it has two sets of teeth. When the crown is pushed in, one set meshes with a gear on the mainspring for winding. When pulled out, that gear releases and the other set meshes with a gear that turns the cannon pinion underneath the second wheel, so the minute and hour hands can be set.

Modules

Complications require additional gear trains to operate calendars, power reserve indicators, chronographs and so on. To accomplish this, many core movements have separate modules from companies like Dubois-Depraz, which are basically prebuilt gear trains that mesh with the base movement. This adds thickness to the movement as an extra layer of components is introduced.

All of Horage’s movements are modular, so the complications are integrated and native to the movement itself and can even be added or removed without the need for external modules. This allows our movements to remain thin and entirely under our development. For example, the K2 micro-rotor in Supersede has four complications and is only 3.6mm thick, allowing the watch case to be only 9.85mm thick. This is quite an achievement, especially with a water resistance rating of 200 meters.

Horage Movements

As mentioned, all of our movements with complications are fully integrated without external modules. Complications can be added or removed as well, and both the K1 automatic and K2 micro-rotor demonstrate this. For example, using the same K1, Omnium 2 has a power reserve indicator and Autark has both a big date and power reserve indicator. The K1 has 18 configurable variations, while the K2 has 38 possible variants via three different configurations, 2.9mm, 3.3mm and 3.6mm. Upcoming K2 watches will have a variety of complications, so stay tuned!

We Want to Hear From You!

Sound off in the comments about additional topics of interest, so we can be sure to cover what you want to read in future articles. And please share this with friends and anyone interested in watchmaking, and let's keep the conversation going. Also, be sure to sign up for our newsletter (here) and keep an eye out for new products as we're always in the process of development. Check out journal entries as well (here) and a detailed section on performance watchmaking at Horage (here).

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Erik Slaven