Mechanical Watch – Bartosz Ciechanowski
Bartosz Ciechanowski
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May 4, 2022
Mechanical Watch
In the world of modern portable devices, it may be hard to believe that merely a few decades ago the most convenient way to keep track of time was a mechanical watch. Unlike their quartz and smart siblings, mechanical watches can run without using any batteries or other electronic components.
Over the course of this article I’ll explain the workings of the mechanism seen in the demonstration below. You can drag the device around to change your viewing angle, and you can use the slider to peek at what’s going on inside:
What you see here is known as the movement – the inner part of a mechanical watch that’s usually enclosed in a metal case. In this article I’m focusing on a watch movement itself, since beautiful watch cases merely hide the intricate mechanisms which are the real stars of the show.
The entire watch movement has a lot of parts, and in this blog post I’ll explain the purpose of each one. The world of watchmaking is jargon-heavy, so many of the components may have unfamiliar names, but you shouldn’t feel pressured to remember them – the names and parts will be color-coded for easy reference.
In a functioning watch many parts are in constant motion. By default all animations in this article are enabled, but if you find them distracting, or if you want to save power, you can globally pause all the following demonstrations.disabled, but if you prefer to have things moving as you read you can globally unpause them and have animations running.
While the entire watch movement has many parts, the timekeeping system, which forms the core function of any watch, consists of just seven major elements which we can lay out in a straight line:
It may not look like much, but these parts still have a lot of interesting details about them that contribute to the second hand rotating at a correct pace. We’ll start exploring these details by focusing on the source of power for this entire contraption.
Power
Purely mechanical devices have a few different ways to power themselves, but one of the simplest methods to store energy is to use a spring. Most springs we see in daily life are coil springs. In the demonstration below, you can move the mass attached to this type of spring to see it bounce:
When a spring like this is compressed, it stores some energy that is then released when the compressing tension is removed. Mechanical watches typically use a different kind of spring – a spiral torsion spring. This type of spring is loaded when it’s twisted. When let go, the spring unwinds in the opposite direction to eventually settle in its natural state:
In a mechanical watch, we ultimately want to show rotating hands, so a spinning motion that a torsion spring provides is particularly useful. A spring in a typical mechanical watch has a slightly more complicated shape – you can see it below in its relaxed state. By dragging the slider you can try to wind it midair, but as soon as you let go, it will snap back to its original shape:
As you can see, this spring is quite strong and it wants to expand very rapidly. To contain the spring we have to put it in a casing known as a barrel :
Once in the barrel , the spring still wants to expand to its original state, but the barrel’s wall keep it in place. This spring is the storage of energy for the watch and its name, the mainspring, reflects its importance.
Unfortunately, we can’t really get any useful work from the mainspring in this state – it has already expanded to the largest possible size. To store more energy in it we need to wind it tightly using the arbor that we’ll first attach on the inner side of the mainspring :
If you look closely, the mainspring has a little hole near its end – you can see it in the center of the demonstration. The arbor has a little hook that grabs onto that hole:
When the arbor is turned, it pulls the mainspring with it, causing it to wind. In the demonstration below, we’re holding the barrel tight, and you can turn the arbor by dragging the slider:
Notice that as soon as you let go of the arbor by releasing the slider, the mainspring will turn the arbor right back. This is less than desired – we want the barrel to turn instead, so that it can power the other parts of the watch. To get some useful work from the mainspring , we’ll have to keep holding on to the arbor and instead let the barrel go when we want to use the stored energy:
We’ll soon see how this is accomplished in practice, but for now we’ll assume that the arbor is held tight and the mainspring ends up rotating the barrel , just like in the demonstration above. Before we finish up with the mainspring and the barrel , let’s discuss two other details that make this mechanism more reliable. Let me bring up the relaxed...