THE ZENITH CHRONOGRAPH
BY WALT ODETS
Zenith is a company with a history extending back to 1865, and is widely recognized for technical innovation and good quality watches. In 1967, Zenith introduced its arguably most interesting technical accomplishment, the caliber 1724. This movement, by substituting a planetary gearset for much of the conventional automatic winding and wheel train, is one of the very rare experiments with changes to the basic concept of a mechanical watch. It is, however, not the 1724 for which Zenith is best known today, but the 1969 3019 PHC, also widely known as the El Primero (right).
The El Primero, soon available with complete calendar (the 3019 PHF), was not only among the first two automatic chronographs, it was a “fast beat” at 36,000 beats per hour. Even by today’s standards, it is also a relatively flat movement (6.5 millimeters). A 13.5 ligne (30 millimeter) design, the El Primero runs in 31 jewels and provides a power reserve of 50 hours. The movement is currently known as the caliber 410.
Illustrated left, with the central automatic winding rotor removed, it can be seen that the 410 is an integrated chronograph design with automatic winding (1) and column wheel (2). The transfer wheel attached to the fourth wheel pinion (3) and chronograph intermediate wheel (4) are also visible. The 410 uses a Glucydur balance and Nivarox I balance spring (5). The movement is generally very well finished, both functionally and aesthetically, and shows obvious care in manufacture.
The fast beat of the 410 requires a particularly large mainspring, and thus efficient automatic winding. This is a accomplished with a very heavy base-metal central rotor carried in ball bearings and bi-directional winding using a click wheel switcher. Illustrated right are (1) the winding bridge; (2) the first transfer wheel, which is driven by the rotor; and (3) the click wheel. As shown in the inset, the click wheel (3) uses springs. The entire system consists of five components between rotor (1) and mainspring barrel (6). An additional reversing wheel, functional only in clockwise turning of the rotor, sits between 3 and 4 and is not illustrated. The winding system appears robust and well-made, although sprung click wheels are sometimes weaknesses in automatic winding systems.
The caliber 410 uses an absolutely classic column wheel design for chronograph functions. Illustrated left are (1) the column wheel itself; (2) the ratchet wheel that rotates the column wheel; and (3) the click operated by the case pushers that rotates the ratchet wheel (and thus column wheel).
Because the Zenith column wheel switching design is so typical of traditional Swiss chronographs, it provides a useful lesson in column wheel design. An enlarged illustration of the column wheel is shown below.
In addition to the column wheel itself (1), all the chronograph switch levers are illustrated. Spring (3) detents the column wheel to discreet positions as it is rotated by the pusher click (2). Lever 4 switches the chronograph intermediate wheel, powering the chronograph center wheel off the fourth wheel (illustrated below). Lever 5 switches the minute accumulator wheel in and out of contact with the chronograph center wheel and provides reset-to-zero. Lever 6 switches the brake lever. In each position of the column wheel, the beak of each lever either lies on top of a column (as with the intermediate wheel lever, 4) or between columns (as with the accumulator lever, 5). It is thus that starting, stopping, braking, and reset-to-zero functions are accomplished and perfectly coordinated.
SPECIFIC SWITCHING FUNCTIONS
The intermediate wheel lever is shown right (2). The transfer wheel from the fourth wheel is indicated at (3), the intermediate wheel itself at (4). The chronograph center wheel is indicated at (5). When the chronograph is stopped, the beak (7) of the intermediate wheel lever (2) rests on top of a column. The entire lever pivots the intermediate wheel (4) away from the chronograph center wheel (5). The intermediate wheel always remains engaged with the fourth wheel transfer wheel (3).
An eccentric screw (above, 6) adjusts the depth of engagement between the intermediate wheel and chronograph wheel. As illustrated (right) the engagement between the intermediate wheel (1) and chronograph wheel (2) must be be precise to minimize wear, allow the smoothest possible starting and stopping functions, and coordinate properly with braking function.
Chronograph wheel braking coordinated by the column wheel may be observed, right. When the beak (1) of the brake lever (2) falls between two columns, the opposite end of the lever brakes the chronograph wheel (3).
As illustrated right, the minute accumulator trip finger (1) is attached to the chronograph center wheel and trips a tooth of the minute wheel (2) once each revolution. The hour accumulator is driven off the minute wheel.
The minute accumulator switching lever is illustrated right (arrows). During reset-to-zero, the minute wheel is moved away from the center wheel and its trip finger with a counterclockwise pivoting of the lever. (The beak of the lever is hidden under the “scrolled” column wheel cover.)
Like intermediate wheel switching and minute accumulator switching, the reset-to-Zero hammers are provided with an adjustment to equalize forces on the registers (right).
© 2021 Bourne in Time Inc.