Tourbillon clock ( # 40 ) introduction

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Some people may say that Breguet would turn in his grave at the very idea of a tourbillon clock. Despite the fact that there is no real reason for a tourbillon mechanism in a clock, I believe the Breguet would have encouraged an amateur clockmaker who, attempting to understand a Great Men's art, reproduced one of his inventions. For the benefit of beginners it is perhaps worth providing a general explanation (and I hope that those more expert than me will be indulgent in judging any possible inaccuracies) of the tourbillon mechanism. Since the mechanical clock was invented, the importance of the oscillating body maintaining a perfectly regular swing has been recognized. More properly , its oscillations must be isochronal (i.e. keeping uniform time whatever the amplitude of swing of the pendulum, balance etc. )

Once this principle was understood it was quickly realized how difficult it would be to achieve this goal and build an isochronal mechanism . It could be said that virtually all attempts to make horological advances were attempts to get more and more accurate results in this direction. For an oscillating body, one of enemies of isocrhonism is friction: between two mechanical bodies, with the air around an oscillating body, or even molecular friction within mechanical components. Mechanical friction is also indirectly influenced by the forces to which all parts in movement are subject ( gravity, change of the speed of terrestrial rotation and revolution etc. ). For the balance wheel of a watch , another enemy of isochronism lies in the fact that the watch is not held in one position for long, but is constantly being moved around, one minute vertical, the next horizontal , the next upside down. The tourbillon compensate for position error. I do not believe this is the proper place to consider in more depth the relationship between friction and isosyncrhonism, but it is vital to keep in mind the concept that each one influences the other. The balance wheel of a wristwatch or a pocket watch moves according to the nominal duration of oscillation of its mobile mass (the moment of inertia).Unfortunately the time (period) of this oscillation is also dependent on friction, which in turn are effected by the position of the balance wheel with regard to its center of gravity and by the forces imposed by the owner or wearer. All kind of forces - including gravity and earth rotation - influence the moving balance and consequently cause a variation of friction .Otherwise variation in the balance wheel's rate of oscillation would be much easier to set up and adjust. This is the reason why watch repairers check the operation of the watch in 4 (or even 8 )positions searching for the best compromise between the time deviations recorded in each position. Breguet thought that a solution to the problem of reducing the effect of forces imposed on a watch by its wearer might be found by varying regularly the relative position of the balance wheel with respect to the watch case averaging - as watch repairers do - the period of oscillation at least on the same plane of the oscillating body. Ideally he should have done the same also on a plane perpendicular to the plane of oscillation , but this is too complex - even today - without the use of modern technology. To implement his concept he put the oscillating body inside a mobile structure, the tourbillon, and in doing so he introduced one of the greatest complications of horology. Here the entire escapement play sits usual role, while the tourbillon turns around its axle, changing continuously the relative position of the balance wheel with respect to the watch case, averaging out any friction which occurs due to the position and motion of the watch. The futility of building a tourbillon into the movement of a mantel clock which normally stands in a firm position, will now be obvious. The only good reason would be to counteract the forces that our planet incurs during its journey through space, but I am not sure that would be a good reason enough. As a matter of fact the decision to build a clock featuring a tourbillon mechanism, arises entirely on my own inability to resist a challenge, because everybody knows how complex it is to build.

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