A cam-actuated chronograph controls its start, stop and reset functions with a flat, shaped cam that slides or pivots, in place of a column wheel. It was created mainly to make chronographs cheaper to manufacture. The Valjoux 7750 uses this system, and many companies adopted it in the 1980s because it was easier to mass-produce.
How does a cam-actuated chronograph work?
Each press of a pusher moves the cam. The outline of the cam then moves the chronograph levers into or out of engagement. The levers follow the shaped edges of the cam. In a column wheel design, they ride over upright pillars instead. A simple way to picture the difference is with switches. The cam works like a toggle switch that moves from side to side. A column wheel turns like a rotary switch. In the Valjoux 7750, designed by Edmond Capt at Valjoux, levers move an oblong cam back and forth to run the stopwatch.
Why use a cam instead of a column wheel?
The main advantage is that the movement needs no complicated column wheel. In the past, that part had to be cut and could not be pressed. A flat cam avoids that work, and keeping costs down was the main reason for the design. There is a small trade-off. Cam systems can feel a little stiffer than column wheel systems in use, although good design reduces the difference.
Where it comes from
Early cam chronographs could only switch on and off. That made it very hard to add a brake to them. Omega’s Calibre 861 of 1968 solved the problem. Its designer, Albert Piguet, added an extra protrusion between the cams. The cam design went on to make the Valjoux 7750 a dependable chronograph. It was also much easier to mass-produce than movements with a column wheel.
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