The mechanical functions of a chronograph
A chronograph is a bit of a magical thing: not only does it measure time but also it can go back and start from zero again. Not like us, who have to settle for the passage of time and its irreparable unkindness without the chance of a reset or catch-up. Don’t they say that lost time is never found again? Well, with a split-time chronograph, it’s possible! Via a single push-button, the functions of the chronograph mechanism are organized into a set of operations which govern the movement of the hands. This means the start function, followed by the stop function, and then the reset. The installation of a second push-button modified this sequence by making it possible to go from “stop” to “start” again without passing through the reset function. It’s very convenient, a bit like the squares on a Monopoly board – although of course you don’t get to pick up money by passing Go again. This way it is possible to pause an ongoing measurement, read it off and then resume it. Other variants have also been developed for the movements of the hands. First of all, the “catch-up” function which makes it possible to visualize an intermediate time before realigning the split-second hand on the chronograph’s second hand. Then later came the “flyback” or “return in flight” function, designed to meet the needs of aviation. Here, with a single pushbutton, it is possible to simultaneously stop, reset, and restart one of the watch’s chronograph hands with a single touch without stopping the others.
The functions in detail
So, the main functions of the chronograph mechanism are therefore, in order: Start, stop, reset. The chronograph is started by connecting the drive wheel of the chronograph hand to the watch movement. This is performed by translation, or the abrupt shift of the clutch wheel against the chronograph wheel; which often causes a well-known – and unfortunate – jump effect at the start. For example, it is entirely possible to move a chronograph hand forward by pressing the start and stop buttons several times, even when the watch is not working. The stop is caused by disengaging the chronograph wheel and thus uncoupling its gear wheels. A brake or stopper then comes into contact with the gearing of the chronograph wheel to prevent any inadvertent movement of the hand. The reset, the last of the basic functions, is produced by a hammer striking a heart-piece – a heart-shaped cam – fixed to the chronograph wheel. The hammer, by exerting adequate pressure on the heart-piece, makes it turn back to its zero, or flat, position against the flat face of the hammer. It is not useful to compare this to the human heart, which can also be set back to zero, but then only once … One last function is counting. It is provided by wheels that make one turn for each half hour or hour completed by the minute counter, and one turn per twelve hours for the hour counter, in order to record time measurements greater than a minute. These wheels are driven either by drag, that is to say via a gear train from the chronograph wheel, or by jump-steps produced by a finger piece that advances the counter wheel by one tooth for each turn of the preceding wheel. These counters all work as part of the same cycle. Equipped with their own heart-pieces, they will be re-zeroed simultaneously when the chronograph hand is reset. All of these functions have to be coordinated. Several eccentric-headed screws or pegs make it possible to adjust the running, movement, or engagement of one piece of the chronograph in relation to the others. Everything clear so far? Shall we carry on? If not, I ask you to go back to square one – but of the article, not the Monopoly board, I mean.
Two systems and three solutions
Two systems and three solutions In order to ensure these timekeeping functions (remember my grandfather!), chronograph mechanisms are organized into two systems and three types of construction. One is called a column wheel system, and the other a cam or shuttle system. The three different types of construction are called: integrated, additional plate, or additional module.
Column wheel system
This wheel is the mechanical command center for starting, stopping and resetting the time measurement functions. It is what manages the movements of rocker-bars, hammers and other levers. The column wheel revolves around a left-hand threaded shoulder screw. The screw can’t unscrew itself, on the contrary, the rotation of the column wheel can only tighten it. It’s easily recognizable by its head with three parallel slots, inviting the watchmaker to turn it in the correct direction. Too bad for the uninitiated! Do watchmakers maybe like to set traps?
Là c’est une came ou navette qui mène le jeu des bascules, marteaux et autres leviers. Cette pièce ne tourne pas mais effectue des allers et retours, d’où le terme navette.
Solution 1, the integrated system
Historically speaking, the chronograph mechanism was originally designed around a column wheel. This type of construction, called integrated, makes it necessary to visualize a specifically chronograph type of movement. It means fitting within the internal space of the mechanism all the components required for the chronograph function: the column wheel, drive wheels, counters, scales, springs, bridges, not to mention the essential eccentric-headed adjusting functions. A chronograph design with a column wheel makes for fairly thick movements in terms of depth, requiring meticulous construction of the components and painstaking adjustment of the functions while putting the mechanism together.
Solution 2, the additional plate
Later, in order to rationalize watch production, the cam or shuttle system appeared. The mechanism combining the ad hoc functions is arranged on a base plate which is then fixed to the bridges of the base movement. In this case it means modifying an existing movement to permit a passage for the axes of the hands which display the chronograph measurements, and visualizing the fixing of the additional board, while simultaneously providing access to the base movement’s balance.
Solution 3, the additional module
The most recent innovation, this solution requiring just a single drive wheel on the base movement, means linking an additional chronograph module at the level of the dial. With this module, there are no axes for the chronograph hands running through the mechanism, and no need to arrange access to the base movement’s balance. This solution makes it possible to produce movements of reasonable thicknesses.
New technical developments
Complementing the keen interest of lovers of Belle Horlogerie, such are not in short supply. Apart from an inherent gain in accuracy, an increase in the frequency of the balance to 5Hz has made it possible to measure in tenths of a second. Not long ago, the irritating problem of the “jump start” was resolved via a vertical clutch. Starting is effected by the vertical movement of two wheels on the same axis; the resulting instantaneous contact between the drive wheel and the driven wheel allows for a precise start of measurement. This device can be offset, making it possible to keep the movement within suitable dimensions. Another development is the linear hammer, which simplifies resetting the chronograph display by reducing the number of component parts, thus limiting the number of adjustments and consequently significantly increasing the reliability of the whole. One latest innovation is the hour counter. While the hands of the chronograph are being driven, the hour counter wheel is released from its continual friction with the barrel, with a consequent balance of forces. Just as when in a car you have emptied the trunk and you raise the rear seats in order to carry passengers, the weight of the car remains constant, as does its consumption. So, several things have made it possible to reduce the energy consumption of chronograph mechanisms. With one fortunate result being an increase in the power reserve, sometimes of more than 60 hours with the chrono switched on. One more parallel between cars and watches: What is true for cars is also true for chronographs: the less energy we consume, the further we can go or the longer we can keep the motor running. So, no need to go faster! And then finally, a chronograph can help you work out your speed too, so all the more reason to wear one!
How to decide on the best choice? Wheel, or shuttle?
So, which is the better solution? It’s important to have push buttons that fit nicely with what the wearer wants. We need to be able to mark the beginning, the end of an operation efficiently. And a light and simple reset is a pleasure all round. Softness and responsiveness in the controls is more a matter of construction than of one system or the other. Reliability is equivalent. Occasionally, a column wheel mechanism can need more manipulations to operate its functions. Efficiency, simplicity, and keeping costs down led to the success of additional plates and additional modules. This was particularly true in the bygone era of utilitarian mechanical watches. Today in this new era of Haute Horlogerie, with its aestheticism and all the levers coming to seek information, the column wheel is the winner; for sure. Watch builders don’t hold back when it comes to the highlights of their product, the bold cut of their bridges. And so, laymen can grasp the rational beauty of this mechanism.
Presentation of our integrated chronograph movement
With the Seed VMF 6710, Vaucher Manufacture offers an integrated automatic column wheel chronograph movement. With total transparency, we have merged in this chronograph movement able to measure time in intervals, the precise timekeeping quality of a chronometer. This precision, validated by the COSC, is reinforced by its high frequency of 5 Hz, and by a variable inertia balance which makes a regulator assembly unnecessary. Automatic winding, a large going barrel and a big, 65-hour power reserve also contribute to its superb timekeeping. As regards the chronograph mechanism, the column wheel is visible via the chronograph bridge, and the vertical clutch plus the linear hammer guarantee sharp and clear time measurement. And in continuity of the watchmaking tradition practiced by Vaucher in Fleurier, each of its 315 components is meticulously finished and decorated