Audemars Piguet 3120
by Suitbert Walter
© February 2004 ThePuristS.com
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Introduction:Audemars Piguet is one of the leading houses in the Swiss watchmaking industry. Frequently referred to as one of the "Big Three," the manufactory not only has a glorious past, but a healthy present and a promising future. With a wide range of movements which have stood the test of time, the bar is set very high for any new movement from Audemars Piguet. One's expectation is simply to see something exceptional, and keeping the range of AP's current models in mind, it's even more difficult to imagine which of the two possible primary priorities they would emphasize: a very thin and elegant movement, or something slightly larger and more rugged? The ideal solution for use in all AP models may be a combination of both, and the relatively large watches of today provide an opportunity for AP's engineers to synthesize these two goals. With this in mind, it was naturally an exciting opportunity to introduce a pre-series example of the brand new, 40 jewels, automatic AP caliber 3120. (Editor's note: in fact, the cal. 3120 possesses 45 jewels, but because the jewels under the date wheel, by industry protocol, are not included in the final published jewel count, the "official" jewel count is "only" 40) It should be noted at this time that the piece being considered is a "pre-series" specimen. As with all pre-series movements, there is only an impression of the end result, that is, the finish is not a consideration. It is the design and manufacturing processes that are, and it's these elements that are being finalized during this stage. Once this rigorous exercise is completed, the first run production will commence, which will then exhibit the usual high quality AP finish. Bearing this in mind, it would be premature to analyze the quality of the 3120's finishing, so any such references to "finish" are made in passing or are directed to items which fall outside of the pre-series construct, such as the wheels and pinions, which are provided finished from an outside supplier. First impressions:My first impressions of this new AP creation are dominated by the wonderfully "sculpted" rotor, which is entirely made of 22K gold - a first for AP. The shape of the rotor is unusual, forming an arc of about 110 degree whereas the usual shape is closer to 180 degrees. While quite beautiful, the shape of the 3120's rotor is predicated on physics, not art. The weight of the rotor is double that of the calibre 2120's rotor and coupled with its smaller circumference (1/3 compared to the cal 2120's 1/2) most of its mass, and correspondingly, its center of gravity, are further from the point of rotation, which should produce extremely efficient winding. The inner part of most rotors are relatively thin and necessitate a riveted or screw mounted weight on the outer diameter. In contrast, AP's rotor is crafted of a single solid piece with a comparatively thick inner part. The thickness of the rotor increases towards the outer edge in two steps, following the shape of the bridges. The clearance between the oscillating weight and the bridges is remarkably small. This, together with the decoration representing the Audemars and Piguet family crests in relief, leaves an impression which may be best described as massive. This impression is consistent throughout the entire movement; even though the 3120 is smaller than the 2120, any part of the main structure (such as the bridges and plates) seem to be made of a solid block rather than from a thin sheet. Additionally, the 3120 is a more efficient design, sporting a larger balance and barrel within a smaller area, which are performance-improving features. In view of this, and bearing in mind that the movement height of 4.25mm isn't very flat, I have to say that it is perhaps one of the most elegant and well proportioned movements I've ever seen.
Removing the rotor, that is mounted to the going train bridge with two screws and positioned with two steady pins, reveals a pleasingly clear, well divided layout: the beautifully shaped balance bridge with adjustable screw-fixed stud carrier, the going train bridge, the barrel bridge, and the automatic winding train bridge. The only visible part of the auto-winding mechanism is the reduction wheel which connects the rotor and the automatic winding train. An immediately apparent special feature is the click, which is engaged by the crown wheel instead of the ratchet wheel - a very sophisticated solution, which, together with an additional driving wheel carried in ball bearings (underneath the bridge), allows the use of a small ratchet wheel and a good, accessible, albeit robust click (the small ratchet wheel provides clearance for the outer part of the rotor, and allows for a larger/taller barrel). The going train:After the first impressions, I'd like to take a deep step inside, to the heart of any mechanical movement: the power supply. Hidden under barrel bridge and ratchet wheel, the mainspring/barrel assembly is one of the most mechanically stressed components of an automatic wind movement. A well constructed and engineered barrel and mainspring is essential for a high-end movement - and the indispensable foundation of a reliable and precise going train.
Externally the barrel has a nicely spiral brushed finish with classical moulurage (the polished ring between the hub and rim); the more important inner surfaces are mirror polished. While the smoothness of these inner surfaces serve a secondary mechanical purpose, i.e., reducing friction if the mainspring comes into contact with them, this lavish treatment is more than what is required, but it is a level of refinement one expects from AP. As with many modern directly driven sweep second movements, the 3120 employs an "off-set center wheel." But the going train of the AP 3120 also reveals a remarkable solution: in contrast to many other movements, the center wheel is driven by an intermediate wheel which is mounted under a sub bridge together with the indirectly driven minutes pinion.
This intermediate wheel drives a pinion that carries the cannon pinion and minute hand at the same time, making them not directly in the power flow. This solution appears to be very sophisticated and well engineered as it is a very elegant way to avoid common problems with under dial trains of movements sporting offset center wheels. Looking at the complete going train, the compact and aesthetically pleasing layout is obvious. The wheels are finished with a circular brushing and a very nice, highly polished moulurage. The original intention in applying this polish close to the center of the wheels was to prevent the oil, which tended to run out of the bearings, from continuing on its way down the edge of the wheel to the teeth. For a contemporary movement, such a decorative element is more likely intended to add a final touch which represents superior quality.
The tooth profile of the 20 teeth escape wheel appears to be quite traditional, compared to most other modern movements. It is equipped with removable cap jewels (KIF-type). The teeth, pinion and pivots are highly polished to a degree to be expected in a high grade movement.
The pallet bridge is ring-shaped, surrounding the balance wheel center and providing the benefit of solid banking walls. The pallet fork itself is polished and nicely chamfered. This is as pleasant a surprise as it is unusual, because chamfering tiny steel parts like a pallet fork is a lot of work, despite any additional aesthetic benefit being hardly visible even if the watch comes with a crystal back.
The balance is a freesprung, adjustable mass type with 8 Gyromax-style weights. The weights and the outer portion of the balance wheel are polished and the arms are matte/sandblasted finished. While the top view may lead to an impression of a very massive part, the lateral view reveals the rim to be extremely delicate. At first sight, the bottom side appears to be roughly and irregularly finished. But a close look reveals the reason: it is ground by hand in an irregular circular motion. This usually is applied to take away the burrs which are left by machining without changing the thickness in an asymmetrical way. Grinding in a straight, regular motion would leave a straight "brushed" finish, but in fact the danger of rounding the edges or changing the symmetry would be much greater. The small slot cut into the rim in the upper right quadrant was made during the initial poising.
The hairspring is laser welded to the collet and glued to the stud - this for sure isn't a traditional method; but if one is looking for the best technical solution, the use of glue is probably state of the art today - albeit somewhat unexpected in a very high grade movement. The Geneva-type stud carrier is adjustable in order to correct beat error and fixed with two screws - this assembly should be a joy for any watchmaker who will have to service this movement. If I were allowed to voice my wishes for an ideal regulating organ, they would be nearly fulfilled by the cal. 3120 - while a Breguet overcoil would be welcome, I have to admit that it probably would not be better, just a bit nicer.
Looking at the beautiful balance bridge, it is hard to imagine a more logical or "better" layout. The use of a bridge instead of the much more common balance cock allows greater precision in critical tolerances, especially endshake of the balance arbor. In terms of long term accuracy, stability and reliability this is truly a superior solution. And once again it is amazing that even the tiniest parts, like the stud carrier or the balance bridge, are very "three-dimensional".
The automatic winding train:
Automatic winding of the new AP cal. 3120 is bi-directional. The outer part of the rotor ball bearing (which is pressed and riveted into the oscillating weight) is the first gear of the automatic train, followed by a reduction wheel which is screwed onto the pinion with a square shaped end part. The two piece construction of this reduction wheel is as elaborate as it is uncommon, even in very high-grade automatic movements.
The rest of the automatic train is completely integrated under the bridge. First comes the switching rocker which is responsible for the change of rotation and bi-directional winding. The principle of a rocker is well known, but there are many different ways to implement it. The AP switching rocker is very compact and sturdy at the same time.
The rocker wheel arbors (which stick out of one of the two coverplates to the mainplate, inclined in two holes in the mainplate) act as a sort of limiter or banking for the rocker action in order to control the depthing into the driving wheel. The riveted rocker is impossible to disassemble, therefore it is extremely difficult to observe that the switching wheels are jeweled as well. A nice detail, but servicing them could be very tricky.
The function of the switching rocker is revealed by the pictures above: on the left, the rotor turns counterclockwise (including the rotor pinion - 4 wheels until the driving wheel). On the right, the rotor turns clockwise (including the rotor pinion - 1 wheel less: only 3 until the driving wheel). As a result, the rotation of the driving wheel always remains counterclockwise - all of this is achieved by a slight turn of the rocker. The winding wheel (the one driven by the rocker wheels) has an asymmetric tooth profile with sharp tips - this allows the rocker wheels a smooth engagement while changing position. In addition the driving wheel works as a ratchet wheel with a click, which is nicely mounted with two pivots between mainplate and automatic train bridge. And it is even fully jeweled, on both pivots! Next to the winding wheel is a further reduction wheel which drives the decoupling/click wheel. This click wheel is necessary to disengage the automatic train while handwinding (otherwise handwinding the movement would turn the oscillating weight as well).
While automatic winding, the four tiny claws are inclined into the grooves and transfer the rotation. Handwinding the movement causes the claws to slide out of the grooves and to disconnect the automatic train. This creates a smooth, silky "click-sound". Finally the torque is transmitted to the barrel through an intermediate driving wheel (similar to the driving wheel between crown and ratchet wheel, both use ball bearings and are press fitted onto the underside of the barrel bridge.)
The gear ratio of the complete automatic train is approximately 150 :1 (rotor : barrel arbor).
Keyless works and dial train:
The dial train is a classic layout with cannon pinion, minute wheel and hour wheel. The second of the three handsetting wheels is rocker mounted and used for the quickset function as well. Like almost all steel parts in the cal. 3120, the rocker is nicely finished, chamfered and straight grained. It has two functions - it is a coupling rocker for the setting wheel train, carrying the second handsetting wheel, and in addition this second handsetting wheel acts as a quickset wheel with its upper part (three claw shaped teeth). Disassembling the rocker reveals a very elaborate detail: the rocker with setting/ quickset wheel is supported by a ruby shim, which is pressed into the mainplate.
Any watchmaker who has ever seen the mainplate worn down by the small setting wheels after years of use will understand how useful this detail will be. Besides, this ruby shim guarantees a smooth and soft rocker action. All three setting wheels and the rocker are separately held in place by screws - the third of the setting wheels is carried by a pressed-in steel pillar. The winding stem is a three position type - winding, date quickset and handsetting (with stop (hack) function). Winding feels very smooth, accompanied by a slight "click" sound. The quickset is activated in the second stem position and works crown-clockwise only (ascending date). It requires only very slight force without feeling loose or spongy. In setting position, the stop lever is activated, and turning the crown clockwise results in a counterclockwise rotation of the hands (because of three setting wheels and the classic under dial train). Setting the hands shows relatively little play in the setting train, which is a sign of tight tolerances. But pushing back the stem shows reveals an uncontrolled slight movement of the minute hand. This is possibly a side effect of the rocker layout as this tends to apply a slight rotational impulse to the setting wheel when engaged or disengaged. The setting lever, setting lever spring and yoke are nicely finished (chamfered and matte brush finish); in particular, the yoke with its guide groove for the setting lever pin is beautifully engineered. The date mechanism features an instant jump date switch which is achieved by two wheels only. The reduction wheel is driven by the hour wheel and is pivoted as well as fully jeweled (a beautiful detail again; so much attention to this wheel is rarely seen). The date wheel is of a complex kind - the basic brass wheel is fitted with an inner steel cage, which houses a pivoted pawl and spring to build up the power for the instant date jump.
Approximately three and a half hours before the date change the inner steel cage of the date wheel is blocked by a release spring (detent) which is mounted on the mainplate beneath the driving wheel and catches in a small groove - the outer brass wheel continues rotation and winds the small inner spring.
At the time of the date change this release spring is pushed aside by a small steel pin which is pressed into the brass wheel underside.
This leads to the release of the inner steel cage with the pawl and the date star rotating for one increment. The complete mechanism is very sophisticated and in my opinion, it should prove to be very reliable. The date star disc is fixed on the mainplate by three beautifully finished retaining screws with specially formed heads.
A 90 degree turn of these screws releases the date ring - a great detail which facilitates servicing (in fact these "screws" are unthreaded friction fit pins). The date star is supported by five convex rubies which are pressed into the mainplate (similar to the setting wheel rocker bar, which is flat however), resulting in less friction and wear, which helps to minimize the necessary torque for date change.
Some points maybe of interest for the future owners of a watch with this movement: it should be impossible to damage or do any harm to the date mechanism whenever or however the date quick set is used. If set through hand-setting, it will work clockwise while counterclockwise nothing happens. If the quickset is used in the period between 8:30 pm and midnight, the usual date switch is missed, but it is impossible to damage anything by setting/quick-setting at the wrong "time window". General comments:Any of the few additional fractions of a millimeter in height was a great investment when AP had the chance to determine the final thickness of the new movement. Even though the general appearance of the movement is most elegant and well proportioned, I did not find a section or part that caused even the slightest doubts in terms of its reliability, stability and structural strength. Apparently, reliability was among the top aims during the development of caliber 3120. I really admire the way they achieved this and I'm sure it will be a new benchmark for quality among contemporary automatic movements. For sure some may regard some of the elaborate details to be familiar, and well known from other manufacturers, but the combination of so many engineering solutions in a single movement, which is so well proportioned, is a really great success. There are only very elements of the design which raise questions, such as the press-fit ratchet driving wheels or the riveted rocker. However, I must admit these reservations are more based on my own, probably more than slightly nostalgic, view of the best approach to mechanical solutions. If I had to express my thoughts in one short comment, I'd say: "this is, at the same time a rugged, reliable sports watch movement, and a classic, beautiful dress watch movement". Only time and many samples in the field will tell, but based upon this pre-series specimen, I think this new caliber has the potential to prove itself worthy to join the pantheon of "the greatest automatic movements ever made." Suitbert
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