BY WALT ODETS
The vertical clutch design offers another benefit difficult to obtain with a conventional switched intermediate wheel. As illustrated left, the upper center wheel pinion carries both the heart cam (1) and a plate with finger (2). The single finger trips both minute and hour accumulators as the center pinion rotates.
The illustration left shows the finger (1) about to trip a tooth on the minute accumulator intermediate wheel. The hour intermediate wheel is on the other side. Because the hour intermediate wheel is tripped once each minute, there are two intermediate reduction wheels between the hour intermediate wheel and the hour wheel itself.
As shown left, both the hour accumulator (1) and minute accumulator (2) are detented by simple steel jumper springs. The jumper springs assure that the hour and minute accumulators indicate whole increments and serve as brakes for these wheels.
Unlike many designs which use separate hammers for reset of each of the three registers, the clever Piguet design uses a single hammer. This simplifies construction and assures uniform reset of all registers. As shown right , the case pusher (1) operates on the reset lever (2), which operates the three-head hammer (3).
The hammers operate against the logarithmically curved heart cams, forcing the cam to rotate until the hammer lies in the "top" concavity of the heart (opposite the apex). This is the zero position for all registers. The center wheel and hour accumulator hammers are indicated at the arrows, right.
The automatic winding mechanism is a modular unit attached to either the "simple" or rattrapante calibers with three screws. The mechanism is cleverly designed so that there are only two small differences between the units used on the two calibers. The rattrapante winding unit uses a longer pinion on the final transfer wheel (1) and one of the three mounting screws is longer. The ball bearing carrying the central rotor is indicated at (2).
The elegantly simple mechanism provides winding with the central rotor turning clockwise (as seen from the movement side). This is accomplished with a single click (arrow). On an automatic winder, the watch must rotate clockwise (as seen from the dial side). The ball bearing carrying the rotor is replaceable by simply replacing the cover of the unit.
Like the automatic winding unit, the rattrapante unit is a discrete module. On the caliber 1186, it is literally sandwiched between the automatic winding unit and the movement. The rattrapante unit, however, requires several changes to the basic caliber, a taller case band and bezel, and the addition of a third pusher at 10 o'clock. Shown at right are (1) the cover; (2) the rattrapante column wheel; (3) the return lever lifting wheel; (4) the split-seconds wheel itself; and (5) the switching arm for the return lever lifting wheel.
Utilizing a relatively simple mechanism, the rattrapante function is comprised of an additional center seconds hand that can be stopped and started independently of the main center seconds hand. The "zero" position of the rattrapante hand is alignment with the main hand, regardless of where the main hand happens to be. The rattrapante hand overlies the main hand in movements with the chronograph mechanism on the top plate (as opposed to behind the dial).
As illustrated right, we see the rattrapante wheel (1), its small heart cam (2), the cam return lever (3), and the return lever spring (4). Note that the spring is actually carried on the rattrapante wheel itself. Because the rattrapante heart cam is carried on the main hand pinion (and aligned with the main heart cam), a "return to zero" means a return to the position of the main hand.
As illustrated right, we see the rattrapante wheel (1), its small heart cam (2), the cam return lever (3), and the return lever spring (4). Note that the spring is actually carried on the rattrapante wheel itself. Because the rattrapante heart cam is carried on the main hand pinion (and aligned with the main heart cam), a "return to zero" means a return to the position of the main hand. Traditionally rattrapante mechanisms have had a major drawback. When the rattrapante hand is stopped, the small heart cam continues to rotate with the main hand. The pressure of the rattrapante return lever on the cam places a significant load on the movement for as long as the rattrapante hand is stopped. For this reason, the rattrapante heart cam is usually shaped with a shallower profile (based on the spiral of Archimedes rather than a logarithmic curve). While this lessens the load on the movement, it does not eliminate the problem.
Right, this useful and clever piece of engineering is shown in greater detail. As the column wheel pivots the ratchet arm counterclockwise (illustration above), the ratchet arm pulls the return lever lifting wheel and its attached pin (4) counterclockwise. The pin (4) hits the return arm (2) lifting it off the heart cam at (3). The heart cam is free to rotate with the chronograph main hand. When the rattrapante hand is restarted, the return lever lifting wheel (4) rotates clockwise and the return lever (2 and 3) acts on the heart cam (1) to realign the rattrapante hand with the main hand.
A rattrapante hand must brake instantly and precisely when the rattrapante mechanism is activated. Like most rattrapante designs, the Piguet design brakes the rattrapante wheel (1) with a high precision scissors brake (3 and 4) operated by the column wheel (2). The column wheel acts on the scissors at the arrows. Brake activation and release are instantaneous, precise, and balanced.
The Piguet chronographs all share the same balance assembly (left), a three spoke Glucydur balance with KIF shock protection.
The fine regulator mechanism (left) is an easy-to-use, low backlash, worm gear mechanism which is much more positive in action than the more common, friction-operated Triovis adjuster.
For originality of engineering and precision of chronograph function, the Piguet chronographs are without peer. For quality of workmanship, they are among a tiny handful of the very best, including those from Lange, Patek, Vacheron, and Audemars. Although more simply decorated than those of Lange or the Geneva firms, the Piguet finish, including functional finish, is immaculate.
Available in a variety of watches, most notably from Blancpain, the simpler Piguet chronographs can offer excellent values. The rattrapante--which carries a US$20,000 premium over the simple chronograph--seems inexplicably expensive. According to M. Humbert, former Professor of Special Chronograph Courses at the School of Watchmaking, Bienne ("The Chronograph: Its Mechanism and Repair"), the distinguished rattrapante return lever lifting mechanism may stem from an 1891 Swiss patent. Regardless, it is a wonderful refinement on the rattrapante mechanism and is, to my knowledge, available only from Piguet.
RETURN TO PART 1 OF THE ARTICLE
