A column wheel is a round control part in a chronograph, with ratchet teeth around its base and upright pillars on top. Its position decides which coupling levers, hammers and brakes can move. So it governs what the chronograph does each time a pusher is pressed.
How does a column wheel work?
Each press of a chronograph pusher turns the wheel forward by one ratchet tooth. A click and a spring usually push it along, so it moves in steps rather than gliding. It is built to turn in one direction only. The coupling levers, hammers and brakes each have a finger held against the outside of the wheel. As the wheel steps round, its pillars and the gaps between them pass these fingers. Whether a pillar or a gap meets each finger decides whether that lever can swing. The wheel’s position after each press therefore sets which parts act.
Is a column wheel better than a cam?
The main alternative is the cam, also called the shuttle. A column wheel steps round in one direction. A cam turns clockwise when the chronograph starts and then moves back and forth. A column wheel is no guarantee of quality. Some cam chronographs are excellent, and some column-wheel chronographs are poorly adjusted. The column wheel also says nothing about the clutch. It sets how the chronograph is controlled, not which kind of clutch it uses. It can be paired with either a horizontal or a vertical clutch.
Where it comes from
Adolphe Nicole made a chronograph design in 1844, but in it the castle wheel did not yet control the reset. Castle wheel is another name for the column wheel. In 1862 Nicole received British patent No. 1,461 for an improved chronograph using a castle wheel ratchet. Longines’ first chronograph, the 20-line reference 20H of 1878, was controlled by a column wheel.
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