pro & con: horizontal vs. vertical coupling - WatchTime

PRO & CON: HORIZONTAL VS. VERTICAL COUPLINGVERTICALMARC A. HAYEK,CEO OF BLANCPAIN:“Blancpain introduced Caliber 1185,with a height of just 5.5 mm, in 1987,and it remains the world’s slimmest selfwindingchronograph movement. It relieson a vertical coupling to avoid two of themost common problems that beset chronographmovements. On the one hand, agentle interaction between two disksstarts the chronograph. This is unlike thesituation in horizontally coupled devices,in which the gears mesh abruptly whenthe start or stop button is pushed. Ofcourse, if the teeth don’t immediatelymesh perfectly, this abrupt coupling cancause the chronograph’s seconds hand tomake a small but noticeable jump. Furthermore,imperfect meshing can damagethe gears. That’s why the owner’smanuals accompanyingeven thefinest chronographsrecommendthat owners avoid too frequentuse of the stopwatchfunction because the additional energyrequired by the chronograph mechanismcan adversely affect the accuracyof the watch’s rate. Both of these shortcomingshave been rectified in Caliber1185 and in all the successive caliberswith additional functions based on the1185. A sudden jump by the chronograph’shand is eliminated. We have alsoensured that the operation of the chronographexerts only a minimal effect onthe watch’s rate behavior.”Top, right: Blancpain’s Caliber 1185, theforerunner of vertical coupling.Left: Blancpain’s Léman Flyback Chronowith big dateContinued from page 84graph’s center wheel, which causes the chronographhand to begin to move. Analogously,when this connective bridge is removed, thehand instantaneously ceases to move.The chronograph’s center wheel and its teethcease their motion, but the movement (includingthe driving wheel and the intermediatewheel) continues to run.Admittedly, this technical description is a bittheoretical and paints a rosier picture thanwhat takes place in horological reality. A certainamount of play is unavoidable whenevergears transfer force, and this play interfereswith the uniform progress of the chronograph’shand. To prevent the notorious lurchingand trembling of this hand, watchmakersuse a little friction spring that presses against ametal disk bearing the finger that advances theelapsed-minutes counter. This spring minimizesvibrations, but it causes unavoidable frictionand also saps energy from the mainspring.The result is a decline in the amplitude of thebalance whenever the chronograph isswitched on. The art of fine adjustment involvesachieving a well-balanced compromisebetween the braking effect and the loss oftorque.Another difficulty associated with traditionalwheel coupling concerns the meshing of theteeth when the coupling occurs. The tooth ofone gear slips into the space between two adjacentteeth on the other gear, and this causesthe chronograph’s hand to jump a bit when itbegins to move. Furthermore, frequent con-88 WatchTime April 2007