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The Minute Repeater by Roffensian

The Minute Repeater

This is a very simplified summary of the topic. It is designed to provide an overview of the subject for those who are interested, but will fall far short of a comprehensive discussion. I hope that readers will have a better understanding of the fundamentals, but they should not expect to receive a detailed description of all elements.

First off, it’s important to understand that not all repeaters are created equal. Ebel make a repeater that can be had for a street price of about $12,000 – it’s not the same as the $650,000 Zenith minute repeater. So before we get too carried away let’s explain the concept of a repeater and then look at the different types. I'll just cover that in this first post, and then I'll add the way that these movements work in a second post.

At the simplest level a repeater is a watch that sounds the hours and potentially the minutes. Think of a long case clock that does the chimes on the hours – one chime for each hour of indicated time. Watches (and clocks) chime hours with a low tone and partial hours with a high tone (sometimes combined with the low tone). Don’t ask me why it’s that way around it just is – always. There is one very important difference between watches and long case clocks however – watches chime on demand, not regularly on the hour as clocks often do.

This made sense before lumed hands and electric light – how else could you tell the time. Today (similarly to the tourbillon) there is no functional need for a repeater, but hey – they’re damn cool.

So what are the different types of repeater? Well, there are quite a few of them:

That’s it in the range of ever increasing repeaters, but we haven’t yet mentioned the granddaddy of them all – the grande sonnerie (hey this is haute horlogerie, there has to be at least one foreign phrase!!). The grande sonnerie combines a repeater (usually a minute repeater) with the ability to strike the hours and quarters on the quarter (not just on demand like the repeater complication). Of course this can be turned off!!

How do these work – heck that is complicated – I need a drink before I attempt that, so I’ll add that stuff later – either tomorrow or next weekend.

In the first post I explained about the different types of repeaters, in this post I’ll try and explain how they actually work. I’ll concentrate on minute repeaters, although the concept is pretty much the same for all types – though an hour repeater obviously only has one ‘gong’ while others need two – a low and a high tone. There are a very small number of watches that have a 3rd gong to avoid the need for the low / high combo for quarters. In this case the 3rd gong is a middle tone. At the extreme are a handful of grande sonnerie watches that have 4 gongs. Any watch with 3 or more gongs is technically called a carillon.

A little bit of history to start with. Repeater watches have been around since the 1680s, only about 10 years after the repeating clock, and the minute repeater was a reality by around 1750. The current way of producing the sound using a wire gong was invented by Abraham-Louis Breguet in the 1780s – the same guy that invented the tourbillon.

Early repeating watches were driven by the mainspring of the watch, but that isn’t a very effective method because it tends to cause the mainspring to wind down very quickly, thereby stopping the watch. The solution was to power the repeater mechanism by a separate spring, but that too had problems because sometimes the spring was not fully wound, and therefore didn’t have enough power to complete the chiming sequence – 11:59 on a minute repeater requires 31 chimes (11 hours, 3 quarters (two chimes each) and 14 minutes). The solution to that problem was to invent a mechanism that only triggered the chiming sequence when the spring was fully wound. By now you can likely guess who invented that – Breguet.

So, we’ve established that the repeater mechanism is powered by a separate spring, and there’s a device that prevents the repeater from operating unless the spring is fully wound, now let’s get technical. Repeaters operate using a process called rack striking, and the mechanism is called a rack and snail mechanism. There is also a gear train that transmits the power from the spring to the rack and snail mechanism and a centrifugal governor which acts like an escapement to control the transfer of power.

The rack and snail part is what actually ‘counts’ the chimes. The snail is a cam that is shaped like a snail - the diameter spirals in towards the centre. This will rotate with the movement of the hour and minute wheels. A minute repeater will have 3 such snail cams – one that rotates with the hour hand and has twelve different settings on it, and two that rotate with the minute hand – one with four settings (for quarters) and one with fifteen settings (for minutes).

The rack part of the mechanism is usually held in place away from the snail, but when the repeater complication is triggered the rack is released and moves towards the snail, with the teeth on the rack triggering the chiming mechanism. The snail stops the rack when the end of the rack reaches it and thereby stops the chime. This is why the cam is snail shaped – because it needs to allow for many different chime lengths (as many as fifteen for the minutes).

Much of the complexity of minute repeaters is that the mechanism has to not only release the three racks in sequence, it then has to return the rack to it’s original position and hold it in place, ready for the next sequence to be triggered.

However, the real key in the repeater is the chiming itself. The gongs in a repeater watch are circular wires with the different tones being created by varying diameters and tensions of the wires. These wires are hit by ‘hammers’ to create the tone, and every single gong and hammer combination has to be tuned by hand to ensure that the sound is both perfect pitch and the right volume. Tuning includes changing the tension of the gong as well as the force with which the hammer hits it.

Once again, a ridiculously oversimplified explanation of probably the most complex complication in a wrist watch, but hopefully it helps you understand some of the basics.