Review: How On Earth Does A Mechanical Watch Work?

If you watched our recent beginner’s guide, you’ll remember that we touched briefly on how a mechanical watch worked—in a quick, but ultimately oversimplified way. If that left you unsatisfied and hungry to learn more, well, your time has come, because how on Earth does a mechanical watch work, anyway?

How Did We Get Here?

Before we dig in deep to the mechanics of Switzerland’s favourite little engine, let’s contemplate for a moment how we even came to find ourselves having this conversation. We instinctively know that timekeeping is important, with many sentient beings already having a natural body clock working within the circadian rhythm to know when to go to sleep.

As humans evolved beyond just sleeping and not sleeping, however, with the move from foraging to cultivating crops, the pinpoint accuracy of time became more important, to keep track of the seasons and to make sure Grog didn’t oversleep and miss his shift. The sun and moon served as convenient indicators of both these things.

By the time the ancient Babylonians got here, however, civilisation had advanced enough to warrant a calendar to coordinate the shipping of goods, the progress of industry—and something else: social and religious communal activities. This added layer of detail that existed outside of the cycles of nature required more complex systems like sundials and water clocks, to fragment the existing natural cycle into unnatural partitions.

By the 13th century, these devices had become mechanical and self-sustaining, powered by weights drawn by gravity in a uniform way that gave increasingly more accurate time. Instead of the regulation of the sun, or water dripping through a hole, clockmakers had devised the escapement, a kind of mechanical capacitor that can store energy and release it for a predetermined and very repeatable amount of time. And sort of like a pre-Moore’s law Moore’s law, it was inevitable to see that technology shrink.

Accuracy improved enough in the 17th century to display finer detail as minutes and seconds. The French actually tried to decimalise timekeeping into a day of ten hours, each with a hundred minutes, each of those with a hundred seconds, but that didn’t last even two years. It was Huygens’ spiral balance spring that really demonstrated the possibility of shrinking the mechanism itself, which, combined with a larger spring for power, allowed clocks to be carried in the pocket—as a watch.

How Does Mechanical Work?

But what does this all mean? Balance spring? Mainspring? Escapement? These things went through a process of evolution to find the optimal balance of accuracy and efficiency, with watchmaker Thomas Mudge settling on a combination in 1754 that—well, is basically the same as what we use today. That’s honestly the case—you’ll find Thomas Mudge’s Swiss lever escapement concept in basically every Rolex, Patek Philippe and most other Swiss luxury watches on sale today. The only real difference is the size.

Let’s go through it. It starts with the mainspring, which lives in the mainspring barrel. That does exactly what you think it does: it’s wound tight, and when it unwinds again it provides power, just like in a clockwork toy. Only, you don’t need to wind it with a key, at least, not anymore, because you can do it with the crown. Many watches also have an automatic winding system that uses the wearer’s motion to spin an asymmetric mass.

So, what happens to all that power? It needs to be geared for hours, minutes and seconds. The first wheel from the mainspring gives you hours. Wheels to the side of that, known as the motion works, convert the speed into minutes, which is fed back to the central hand stack. For seconds, three more wheels are needed, with the fourth wheel itself driving the seconds sub-dial, or feeding the power back to the central stack for central seconds.

You might be wondering, however, what stops the spring unwinding as fast as possible, spinning the hands around at a million miles an hour? That’s where Thomas Mudge’s Swiss lever escapement comes in, and it’s by far the cleverest part of the whole mechanism. Think about it like this: if you had a bucket filled with water with a big hole in the bottom, left unchecked it would simply empty as fast as it could. But let’s say we wanted to control that flow, to, say, one millilitre per second—we would need some way to only allow the right amount to escape, and to do it routinely once per second.

What you could do is block the hole with a spring-loaded flap. Push the flap and it opens and water comes out, let go of the flap and it closes again, and the flow stops. But how to control the volume and regularity? With a wheel, spinning once per second, that has a protrusion that pushes the flap open once every rotation for long enough to release one millilitre. This has effectively regulated the system, allowing just the right amount to come out at the right time, every time. How could we power this wheel? Why not with the water dribbling through once per second? Each millilitre pushes the wheel just enough to make it through to the next rotation.

That’s basically what we have in the Swiss lever escapement, but instead of water, we have torque from a spring. And instead of a bucket with a hole, we have the escape wheel, that left unchecked will spill out all that torque. Then there’s the pallet fork, which is like our flap, that can jam and release the escape wheel to control the flow of torque. There’s also a wheel with a single tooth, just like our hypothetical water clock, but instead of pushing a flap once per rotation and releasing water, it pushes the pallet fork once per rotation and releases torque. That’s the balance wheel.

How is the balance wheel powered? Like our water system, with the very power it’s trying to regulate. The mainspring power pushes the balance wheel, which unjams the pallet fork, which allows the escape wheel to turn, which starts the cycle over again, powering the balance wheel, unjamming the pallet fork, allowing the escape wheel to turn. It’s a delicate balance arrived at with complex mathematics and precision engineering—which is why it remains virtually unchanged for centuries.

Hopefully that gives you a little bit more insight into how the mechanical watch provides accurate timekeeping from nothing more than the power of a spring. If you enjoyed this video and want to see more like it, why not let us know down in the comments. And if there’s any other aspect of watches and watchmaking you’d like to see explained, please let us know as well!

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