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A DEEP DIVE INTO

HOW THE MECHANICAL 
WATCH WORKS

by Nathan Hardy
Time. A simple thing we as humans devised precision instruments to observe and separate the day to provide a little bit of organisation to our lives.

But is it something we take for granted? We wear our mechanical watches on our wrists because we like the look of them. We like how they feel. How they complement an outfit. The confidence they give us. The talking points they provide. Notice how I missed out to tell the time, we all have phones now. But I feel there is more to be celebrated with these artifacts we have possession over. It’s taken us quite literally thousands of years to get to the point of being able to wear a watch on our wrists that can accurately tell us the seconds, the minutes, the hours, the day, the date, the month, the year, and the phase of the moon that needs adjusting by a single day only after 577.5 years, whilst still doing all those things previously mentioned. Yes. Perpetual Calendars do all that.
IWC Portugieser Perpetual Calendar Tourbillon IW504505

Look at the watch you have on your wrist right now. What do you see? What do you notice? The perfectly chosen strap or bracelet? The carefully sculpted case? A well-balanced dial? Or the sweeping seconds? Do you ever think how the sweeping motion comes to be? Hopefully by the end of this, you will have a better understanding of what goes on within your beloved timepiece. There is a lot to get through, but we’ll start at the beginning. 

Those with mechanical watches will be familiar to hand winding their timepiece via the Crown or Winding Button, but what does that do? Hidden between the dial, caseback and movement plates is the powerhouse of your watch. A coiled spring known as the Mainspring. This is what stores the energy to drive a train of wheels and gives you the power reserve of the watch. When we turn the Crown, a group of meshed gears knows as the Keyless Work turns an arbor that is connected to the Mainspring, coiling it up, storing energy, known as potential energy.
The mainspring positioned inside the barrel attached to a central barrel arbor
The mainspring is kept inside the barrel highlighted in red.

This energy travels through a selection of wheels, known as the gear Train, which reduces the torque (turning force) from the Mainspring, but increases the amount of rotations each wheel does as we go further down the Train. Simply, the further down the wheel Train we go, the less power there is, and the more rotations the wheels are doing. Each gear in the Train has a specific number of teeth which dictate how fast they turn which comes in to play when you start adding hands into the mix, but this will be discussed later.
An example of a typical gear train

Let’s jump into the specifics now. At the end of the Train is the Escapement consisting of an Escape Wheel and a Pallet Frame that has jewels at one end, and horns at the other. In most cases it will be a Swiss Lever escapement, but others do exist and there are variations of the Swiss Lever also. Using the power from the mainspring that’s travelled through the Train, the Escape Wheel rotates on its pivots, just as another wheel in the train, but the teeth are shaped differently, more “boot shaped”. These stronger teeth work with the Pallet Frame jewels to stop the Mainspring from completely unwinding and frantically spinning the Train at high speeds. This quite literally locks the whole Train in place, which is quite a feat considering its size, but it is one reason the power needs to be reduced through the Train. At this point, the components are getting incredibly small and are very delicate.
From left to right, the Escape Wheel, Pallet Frame, and underside of a Balance Assembly from an IWC cal 401. From the underside, the Impulse Pin and Roller can be seen highlighted in red.

Now, there’s no point in having a completely locked up Train, so in comes the next group of components, the Balance Assembly, which is the most delicate part of the watch, and the most hypnotic. The Balance Assembly consists of a few features. The Balance Staff. The Balance Wheel. The Hairspring and an Impulse Jewel attached to a Roller. There are more features, but for this discussion, I will leave out the other aspects. The sprung Balance Wheel turns with the Staff and Roller, and this allows the Impulse Pin to pass into and through the Horns at the opposite end of the Pallet Frame to the Escape Wheel. This interaction makes the Pallet Frame pivot from side to side and in doing so releases the Escape Wheel tooth by tooth which is under the power from the Mainspring. The Escape Wheel turns, the Train turns and so the Hands move. A reciprocal action occurs as the teeth on the Escape Wheel are specifically shaped to push the jewels on the Pallet Frame helping to move this from side to side and in turn, push the Impulse Pin, which maintains the oscillations of the Balance Wheel. Under the influence of the Hairspring the Balance Wheel returns and that cycle is repeated, but with the Balance Wheel moving in the opposite direction thus the Balance Wheel spins from side to side, flicking the Pallet Frame from side to side, releasing the Escape Wheel and the power from the mainspring turns the Wheels and gives the Balance a regular push. As with all technical descriptions, they just need to be accompanied by roughly “hand drawn” diagram, and so here they are to help visualise how this movement actually works.
Okay, and breathe.

We are all familiar with the “tick tock” sound of an old clock and if you listen closely to your mechanical watch, you will be able to hear this ticking sound, just much faster. Yes, it is okay if you now raise you watch to your ear to “listen to your watch”. That ticking sound comes from this action of the pallet jewels interacting with the Escape Wheel teeth. The sound slowed down would be two quick “ticks”, followed by a pause. The first “tick” is the unlocking of the Escapement as previously mentioned, followed by the locking of the Escapement being the second “tock”. The pause is where the Balance Wheel spins around to its outer arc, and then swings back. Obviously, if you did listen to your watch, you will know that this occurs much much faster. Each incremental “tick” of the pallet frame locking and unlocking the escape wheel is known as a beat, or half of a full oscillation of the balance wheel. A typical IWC Portugieser has a frequency of 28,800 beats per hour (bph), which equates to 8 beats per second. So very fast.
IWC Portugieser Automatic IW500714

Frequency is measured by two terms, one we have discussed, beat per hour, the other is hertz (Hz). Hertz refers to the number of full oscillations the Balance Wheel does in a single second. So, we know that an IWC Portugieser does 8 beats per second, and we know that a beat is half of a full oscillation, meaning the Portugieser does 4 full oscillations per second, and so has a frequency of 4 Hz.

Usually, the Second Hand is attached directly to the 4th wheel, and so each time the train is allowed to incrementally rotate because of the unlocking and locking of the Escape Wheel, the Second Hand moves with that same increment. In this case, the 4th wheel is allowed to rotate four times a second, and so the second hand moves position 4 times in a second.

This is what gives you that smooth sweeping Second Hand.
A vintage IWC watch with a sweeping second hand

Some watches will have a higher frequency and some lower, but if you look closely, and slowed it down, your second hand is making tiny incremental jumps. Pretty cool, right?

As we mentioned earlier, each wheel in the Train has a set number of teeth which dictates how fast that wheel will turn. There is a specific formula using the wheel teeth numbers and pinion leaves, which when used, will result in the frequency of the watch. These are also specific to create certain ratios for wheels turning at specific speeds. Typically, the Centre Wheel will complete a full revolution once in 60 minutes, and the 4th wheel will complete a full revolution once in 60 seconds. So, you can start to see this is where we add in a Minute Hand and a Second Hand, but what about the Hour Hand?

We know that there are 24 hours in a day, and we break that down into 12 hours on each side of noon, and that is what we see on our watches. We also know that the Centre Wheel that holds the minute hand goes round once in 60 minutes, but to get the hours, we need to make a 12:1 reduction ratio, in order for the hour hand to rotate fully once in 720 minutes, or 12 hours. This is done via a group of wheels known as the Motion Work, which again have a specific number of teeth to create this ratio. So, for every 12 times the Minute Hand goes fully around the dial, the Hour Hand will go round once, all whilst the Second Hand is sweeping away gracefully.
The view of how the hands are attached beneath the dial

I think it is clear to see that there is a lot going on inside your watch, and here we’ve only discussed a basic time only timepiece, when we start to add further complications, things get more interesting, but I will leave that for another day!

Time. A simple thing we as humans devised precision instruments to observe.
IWC cal 401



Nathan Hardy
With a technical mind, a passion for design, and a keen interest for watches, Nathan chose to study Horology at Birmingham City University, currently undertaking the designing and making of a horological timepiece, alongside completing a selection of complex services to aid his portfolio. This allows him to have an understanding for the inner workings of watches, of which he is keen to share and raise awareness.