Watchmaker’s Bench: What Makes It Tick? (Part 2) – The Escapement

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In Part 1 of our “What Makes It Tick” series, we touched on the mainspring, which stores the power that drives the movement. The release of that power, however, needs to be controlled in some way. This is where the escapement and balance assembly come into play.

There are a number of different styles of escapement, but for the sake of simplicity we’ll focus on the most common style we see today: the Swiss lever escapement. Over the course of this article we will examine each component of the escapement in detail.

The Escape Wheel – Explained

The escape wheel plays a very similar role to one of the gear train wheels, but it’s technically part of the escapement. It is the link, as it were, which connects the escapement and gear train of the movement. The escape wheel rotates like a train wheel, and its purpose is to transfer the energy from the mainspring to the balance. However, it only interacts with one wheel, unlike train wheels, which generally interact with two, or with one and the barrel. Instead of interacting with another wheel, the escape wheel interacts with the pallet fork, which is what simultaneously blocks and releases the power from the mainspring.

The escape wheel in the movement with pallet fork removed.

The Mechanics

The escape wheel has specially shaped teeth that are designed to interact with the pallet fork, which is how that power from the mainspring is able to be transferred to the balance. The escape wheel will have a varying number of teeth depending on the vibrations per hour (vph) of the movement, but more on that later. Escape wheels are commonly manufactured from steel, unlike train wheels, which are made from brass.

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Pallet Fork – Explained

The pallet fork is the component that allows transfer of power between the escape wheel and the balance. The pallet fork is designed to block the transfer of power once it is installed, but as it pivots back and forth, the power is released from the escape wheel, one tooth at a time. Without the pallet fork in place, the train would spin freely.

The pallet fork.

The Mechanics

This pallet fork is an anchor-shaped object usually constructed from nickel-plated brass. It has two synthetic ruby stones that act against the teeth of the escape wheel. At the other end of the pallet fork we have “the horns” and a notch in between. The roller jewel, which is attached to the balance, sits in this notch.

When the watch is wound, the pallet fork will naturally sit with one of the two ruby jewels against a tooth of the escape wheel. This is because the train is trying to let that power out, but the power cannot escape until the balance is in place.

It is important to understand that, at this point, the balance does not provide power to the pallet fork. It is, in fact, the other way around. More on this in a moment.

So now that we’ve gone over how a watch lets power flow to enable time-keeping, let’s move on to the regulation of that power.

The Balance – Explained

The balance is a watch’s regulating organ. Without it, we would have no way of controlling the power that has been transferred from the mainspring.

As I wrote above, the balance receives power from the pallet fork. But how?

The balance viewed from underneath.

The balance is made up of several components. We have the wheel itself, the balance spring (otherwise known as the hairspring) and the aforementioned roller jewel (there are several more parts within these parts, but we’ll leave them out for the sake of simplicity).

The roller jewel sits underneath the wheel and it interacts with the notch of the pallet fork. As the balance oscillates back and forth, the pallet fork “kicks” the balance around through that roller jewel. Each time the roller jewel passes through that notch, it gives the balance energy that allows it to run.

The Mechanics

As the balance oscillates, the roller jewel does the same. When the roller jewel meets the notch of the pallet fork mid-way through its swing, the pallet fork jewel that is resting on the tooth becomes free. At the same time, the opposite jewel lands on the next tooth. This allows the power to escape and the escape wheel to advance one tooth forward.

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The balance wheel never makes a full 360-degree turn, instead traveling roughly 300 degrees when fully wound, which is what your amplitude numbers relate to. An oscillation is two vibrations, which you may be familiar from vph rates (21,600, 28,800, 36,000, etc.). A vibration is one movement of the balance wheel, which allows one tooth of the escape wheel to advance forward, and an oscillation is the combined movement forward and back, which allows two teeth to advance forward.

Side view of the balance and spring.

This happens over and over again at great speed, which gives the appearance of a watch running smoothly. The speed at which this happens depends on the frequency of the watch: 21,600, 28,800, or 36,000 vibrations per hour. The higher the number on this scale, the faster the balance will oscillate and the faster the power will be allowed to escape.

But how do we ensure accuracy here? Let’s turn to regulation.

Regulation Explained

For a watch to keep accurate time in all positions, we must first ensure that the balance is equally weighted all the way around. Any heavy points will impact the timekeeping. To remedy inconsistencies, a watchmaker will add or remove material from the rim of the balance to ensure even weight distribution.

We then can use the hairspring to ensure the watch is regulated to the speed at which we want the wheels to advance. If you recall from our first article, the seconds hand is fitted onto the 4th wheel (or the pinion if it’s geared back to the center). Our regulation goal is to ensure that the 4th wheel essentially makes one full revolution in exactly 60 seconds. If it does, we have perfect timekeeping.

To get to as close to perfect as possible, we need to control the active length of the hairspring, and this is done through curb pins. These are two small pins that come out vertically from the regulation arm that sits on top of the balance bridge. The outer curve of the hairspring will sit between these two pins and it can be moved back and forth along an ark. This in turn either shortens or lengthens the operating length of that spring, which will impact the timekeeping. If we lengthen the active portion of the hairspring, then the watch will run slower. This is because the balance takes longer to return to a fixed point as the balance is allowed more time to complete its oscillation. Conversely, if the hairspring is shortened, the balance will complete its oscillation faster, which means that the wheels will be allowed to let their power escape quicker.

The next logical question to ask then is this: How exactly does this all end with the time I see displayed on a watch dial? The next article in the series will discuss the keyless work and set hands mechanism, which will give us an in-depth look at exactly how the time is displayed and set and how the mainspring is wound inside the barrel.

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Ashton Tracy started his career at 18 as an ambitious young watchmaking student. Having worked independently and for some of the biggest Swiss brands, he provides a unique writing perspective being able to draw on his technical background in the watch industry.
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