© January 2005 ThePuristS.com
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Jaeger-Le Coultre is synonymous with fine Swiss watchmaking for watch aficionados around the world.
Often referred to as "the manufactory", it is one of the most fascinating of all watchmaking firms when it comes to
movement development and manufacturing. Many glorious and famous watchmaking houses, most of them better known to the
general public, were supplied and often
completely dependent on the base movements delivered
by Jaeger-Le Coultre. Over the years JLC’s focus of movement
development continuously changed, from pocket watches of all sizes and complications to incredibly tiny lady's watch
movements, and from hand wound movements to automatic. With relatively
few exceptions JLC calibers are frequently
considered to be "finer" and "dressier", which is not surprising, considering their client companies. Their variety
of different calibers is probably unmatched by any other manufacturer. However, even with this diversity, there were
some gaps in their range- one of the most significant being the absence of a more rugged and sturdy automatic movement,
designed to be a base caliber for a new generation of equally larger and "sportier” watches.
The Automatic Winding
A nice piece of watchmaking and certainly one of the highlights of the new movement is the rotor. The rotor is a two-part construction: the inner part is decorated with circular Geneva stripes and comes with a cut out section for more flexibility, and has a shape traditional for JLC movements for many years. The outer part is a massive 22 carat gold weight, riveted to the rotor. Flexibility in this part is very important; the rotor is quite heavy, with most of its mass at the circumference, and damage to the mounting and bearing otherwise would be very likely. (rotor detail).
A closer look leads to the first surprise: the ceramic ball bearings of the oscillating mass. Steel ball bearing rotors were first introduced by Eterna in 1948, and this design was at first regarded as ideal. Nonetheless, actual use over long periods of time revealed problems which were, surprisingly, not entirely solved until today. And, as it is so often, the main problem turned out to be the worst enemy of a "perfect watch": lubrication.
Larger ball bearings, commonplace in many mechanical applications, are usually lubricated. Sometimes this is a closed, oil filled environment like a car gearbox, for example, and sometimes the ball bearing itself is hermetically sealed with a "lifetime" filling of grease. These methods are impossible for a watch movement for different reasons; the closed environment filled with oils obviously wouldn't be very realistic in close proximity to the balance and escapement, and sealing the ball bearing would create such an enormous amount of friction as to make efficient winding impossible.
Dry ball bearings, without any lubrication seemed to work fine at first, but proved over the long term to be problematic; the steel balls running on a steel surface tend to create contact corrosion. A minimum amount of lubrication may offer a satisfactory compromise, but lubricating correctly is extremely difficult. If the state of the lubrication changes, or is even slightly excessive, the balls tend to slide first instead of rolling, which leads to excessive wear, friction and again, contact corrosion. It is this problem which recommended a simple jeweled pivot to some manufacturers, which in many movements is still in use today.
The ceramic ball bearing in the new JLC caliber 975 is a so called "hybrid" type: a combination of ceramic balls with an inner and outer steel body. In this case it's stainless steel, and even the ball separator (the tiny metal shim which separates the balls and keeping them equally distant) is stainless steel. Jaeger-Le-Coultre, together with the supplier, undertook a significant amount of testing. Among the possible materials for the balls, the primary candidates were steel, ceramic, and ruby. The superior properties of both ruby and ceramic over steel were obvious, with ceramic impressively outperforming even ruby in long term testing. One factor tipping the scales against ruby is that it is prone to breaking under heavy shocks - a particularly important issue considering the heavy rotor.
The exact ceramic material is zirconium oxide, which has almost the same temperature modulus as steel – that is, both expand to the same degree when heated, which is a benefit where critically tight tolerances must be maintained. The main advantage of this combination is, of course, that absolutely no lubrication is required. (As an interesting side note, this independence from lubrication makes hybrid ceramic ball bearings ideal for use in difficult environments like turbo chargers, or in pumps where the bearing is working in liquids - like blood pumps). This surprising capability may sound unbelievable, yet the reduced friction isn't just a "paper spec" - it's obvious even under naked eye inspection. And what may appear as a small modification to a well known concept could very well turn out to be one of the few true improvements of recent years.
The caliber 975 is to my knowledge the first JLC movement with unidirectional winding - it's said that this decision was made after intensive research which demonstrated that unidirectional winding is actually more efficient. (As an interesting side note, the well-known ebauche manufacture, A. Schild, is said to have discovered this in the mid-1950’s. AS was one of the largest movement manufacturers of its time.)
The center bridge, supporting the rotor and housing the automatic winding train, is an
interesting two layer design. With this design it is possible to dismount the entire bridge,
including gear train, without actually disassembling the train. This is a very service friendly
solution but I'm not sure if this is the only reason for this design; as shown in the pictures, the
mainplate has plenty of unused space because the lower pivots of the auto winding train all are
settled in the lower layer of the center bridge. Although this is purely speculation on my part,
it seems to me that this layout offers considerable space for the addition of future complications.
On closer inspection, the automatic winding train looks fairly simple, and some elements are reminiscent of other well known JLC calibers. Due to the layout there is no need for any sort of reverser, which is the main reason for the straightforward looking automatic train. Actually the entire winding train consists of 4 wheels only. Of course fewer parts tend to minimize friction and improve efficiency. Starting from the rotor, torque is transmitted to the train with a rocker mounted pinion fitted with ceramic ball bearings as well (detail). This rocker mounted pinion serves the additional purpose of delivering torque only counter clockwise; when turning clockwise, the asymmetrical tooth profile of the following winding wheel simply lifts the rocker mounted pinion free of engagement with the following wheel (click here for animated graphic clockwise or counter clockwise ). The winding wheel is combined with a click that has jeweled pivots; it may be surprising to see a jeweled click, but this seemingly simple part is incredibly important for efficient and reliable operation of the automatic winding mechanism. Next to this comes a reduction wheel, with the last part of the train being the ratchet driving wheel.
This ratchet driving wheel is a commonly used design with a claw shaped spring for unidirectional
connection to the mainspring barrel ratchet wheel. If the pinion of this wheel is driven counter clockwise
(by the ratchet wheel during hand winding) the claws (which are connected to this pinion) are lifted free of
engagement with the holes in the ratchet driving wheel, and the automatic winding train is disconnected from
the barrel ratchet wheel. This simple solution is time tested, reliable and efficient.
To my personal delight the oscillating system includes a variable inertia type, free sprung balance. Unfortunately the hairspring doesn't have an overcoil, but in practical terms this can’t really be considered a serious omission; legions of movements with flat hairsprings with excellent accuracy give clear evidence of their ability to be very good and precise timekeepers. The balance features four square headed mass screws for rate and positional adjustment. The hairspring stud carrier is movable and is secured in position by a screwed down locking plate.
Instead of a more traditional balance cock the cal. 975 uses a balance bridge, a feature which is increasingly common in new movements developed in the recent past. A closer look reveals two raised areas below the balance bridge in order to secure the hairspring from excessive deformation under heavy shocks, which I regard as a well thought out and useful detail.
The hairspring is laser welded to the collet and stud; the stud, although simple in appearance, is well thought out. At the point where the stud screw holds the stud, a small, surrounding groove is cut into the stud. The stud "head" has a slot like a screw, which makes for a very service friendly detail, allowing one to first secure the stud lightly and then center the hairspring coil by slightly turning the stud with a screw driver seated in the slot. Simple but very helpful!
The large pallet bridge, entirely surrounding the balance arbor, comes with solid bankings
instead of banking pins press fitted to the mainplate. Obviously this design is the natural and most
logical choice today when taking into account modern CNC production capabilities. Historically, this
design inevitably led to significantly higher costs when compared to banking pins, which made it a relatively
rare detail usually found in movements bearing the Geneva seal (which explicitly specifies this detail).
The escape wheel shows exemplary attention to the functional details; the impulse surfaces are perfectly polished and significantly rounded. It's extremely difficult to reach such a high degree of finish in areas where, at the same time, the highest precision is essential.
The escape wheel pinion is slightly unusual as well and, different from conventional practice, the teeth are not cut out along the whole length of the pinion, thus leaving a cylindrical undivided portion towards the end. I'm not sure if this is intended to serve any specific purpose or if it is simply an artifact of the production process; but there is a benefit: the "seat" for the escape wheel, which is riveted to the pinion exactly at that point, has a much larger surface and thus is better supported for running flat and true.
The Going Train
The cal.975 going train is of surprisingly classic style, and as straight forward as can be: a small seconds layout and traditional center wheel (driving the minute hand directly and placed in the center), a truly pure going train par excellence. This traditional design became slightly unpopoular in the 1950’s as the trend towards the use of a center sweep second arose, causing the traditional small seconds arrangement to be perceived as old fashioned. Interestingly the small seconds design was able to secure its position in the field of high precision chronometry, with examples to be found among movements used in the legendary observatory competitions. Obviously "simple is best" is especially true when minimizing friction is the main goal.
As in most modern automatic movements the center wheel pinion is fairly large, leading to a relatively fast turning mainspring barrel. To explain this concept it is important to note that any individual gearing (that is, any single wheel and pinion combination) tends to produce a slightly uneven power transmission. Therefore, if the actual force at the escape wheel were to be continuously measured, a certain amount of fluctuation would be observed. The slower and longer lasting these cycles of fluctuations are, the more they adversely affect timekeeping. In addition, the gear ratios in the train are also important in this regard; the larger the reduction from wheel to pinion, the more the effect of power variations tends to be amplified. For these reasons a center wheel pinion which is relatively large in comparison to the mainspring barrel tends to reduce the fluctuations in power delivery. In addition, the cal. 975 also offers a novel tooth profile, designed to produce as even a flow of power as possible as the tooth surfaces roll across each other.
As is expected in a modern movement, the cal.975 has a "hack" feature, allowing the watch to be set to the precise second. By pulling the crown, the setting lever activates a long, flexible stop lever which contacts the balance rim, stopping the movement. Due to its flexibility no harm is done to the extremely delicate balance pivots.
The barrel arbor is jeweled in the bridge and mainplate, which is considered standard practice for today’s automatic winding movements; this is a high side load area, and jewelling here serves two purposes - prevention of wear and promotion of winding efficiency by reducing the friction the automatic winding train must overcome to wind the mainspring. The later is also the reason for the interesting crown wheel design.
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Instead of the common arrangement of a crown wheel directly geared to the ratchet wheel, the cal.975 features an assembly of 3 wheels; the crown wheel, a first intermediate wheel, and a rocker mounted double wheel which is geared to the ratchet wheel. The rocker is pivoted to the first intermediate wheel. Thanks to this sophisticated solution the partial gear train that is necessary for handwinding (mainly crown wheel and winding pinion) is disconnected during automatic winding, thus minimizing friction simply by the use of fewer parts. Another obviously well engineered detail is the screw gib attached to the mainplate engaged to the setting lever axis. This is different from most common push button release designs, where the setting bridge performs the function of retaining the setting lever (and stem) in place; often this is a point of weakness in conventional designs and cal. 975 seems to offer a considerable improvement in this regard
The Bottom Plate, Calendar Works and Second Time Zone
The bottom plate incorporates the date mechanism, a second time zone, 24 hour day/night indication and of course the usual underdial train with keyless works. The second time zone hand is directly connected to the main hour hand, which at the same time explains the need of an additional 24 hour day/night indication. Without this, an unambiguous reading wouldn't be possible.
The core of the second time zone mechanism is a double, concentric hour wheel. These two parts are telescoped into each other while being connected by a star shaped portion and a claw shaped spring. This star wheel part features 12 cut out sections where the lobe shaped ends of the claw spring find their place. This way, one part can be switched in 12 increments related to the other part, i.e. the second time zone hand can be adjusted in full hours only.
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The upper hour wheel part, which indicates the "home time", drives the 24 hour day/night indicator wheel by a small intermediate wheel. The lower "local time" part directly gears with the date driving wheel (which makes 1 revolution within 24 hours). The cal. 975 date switching mechanism employs the principle of "Maltese cross" works: on top of and coaxial with the main driving wheel is a round disc with one switching finger surrounded by two cut outs on both sides of the finger. The Maltese cross gears to this disc with switching finger, which results in a quarter turn of the four leaf Maltese cross wheel for each completed revolution of the large driving wheel. The Maltese cross wheel itself is geared to the date disc; this quarter turn of the Maltese cross wheel equals a date advance of one day.
Maltese cross date
Due to this special date switching design, the date star disc doesn't need any sort of jumper and spring. As the date disc is constantly geared to the Maltese cross wheel, which itself is blocked during the inactive period due to its special design, the date disc is firmly held in position. The lack of a spring-driven jumper is a benefit, as the date disc doesn't need to overcome the resistance of a spring. Thus friction and any other disturbing forces to the balance are minimized relative to many other designs which employ jumper springs to hold the date wheel in position- in fact the friction associated with the date change, and any drop in balance amplitude, is probably negligible. As is so often the case even this advantage comes hand in hand with some slight drawbacks; this construction does not allow for an immediate quickset of the date and the process of changing the date requires a comparatively long time (about two hours). Changing the date for one day takes about 5 1/2 revolutions of the crown (pulled to first stop, second time zone setting position) however a change in both directions is possible.
The Keyless Works
Except for the first wheel, the entire setting wheel train is mounted to a rocker bar. This rocker bar pivots coaxially with the first setting wheel and is activated through the setting lever. A small pin, riveted to the setting lever, sits into a cut out groove of the rocker bar. This groove is shaped so as to guide the rocker bar to the different setting positions: neutral position is winding only; first position pulled out is for setting second time zone ("local time") in 1 hour increments and semi quick set for the date; second position is for setting "home time". This is the only position in which setting the minute hand is possible; and in addition the stop lever will stop the balance wheel; in this position both hour hands of course are synchronised. All three setting wheels mounted to the rocker bar are riveted to it; therefore disassembly is not possible. The setting lever spring and yoke with spring are in one piece; each are attached to the mainplate with help of only one screw; obviously nicely optimized for ease of assembly.
Click for animation of the keyless works
My Personal Impression and Conclusion
From a manufacturing standpoint it is very interesting in several respects; in addition to extensive use of new technologies and materials in the movement itself, I would also be inclined to say that the design is intended to provide optimum results given modern manufacturing methods and techniques. For example, every bridge, cock and plate comes with several, relatively large, positioning holes (detail picture 4). The underlying issue this is intended to address is a key problem in CNC manufacturing: the precise placement of parts. Usually this is achieved by using some of the functional holes (or pins) of the plates, cocks and bridges to index the part; this often results in considerable wear and loss of precision for the holes or pins, which are important parts of the completed movement. Adding these indexing holes, which serve production purposes only, certainly is a very good and useful idea, though admittedly distracting in terms of aesthetics.
A Jaeger-Le Coultre specialty are the threaded holes in bridges, plates and cocks, which are of the "raised hole" type; this means the threaded hole is surrounded by a raised portion concentric to the hole. This raised portion assumes the function of the formerly common steady pins, indexing the bridges and cocks to the plate with highest possible precision. Interestingly these thread holes are bushings, thus building the raised portion around the thread hole; thanks to modern CNC technology this seemingly more complicated design is in fact easier to execute. This design has been characteristic of Jaeger-Le Coultre for some time, but I found it to be none the less up to date with modern production methods.
Apparently a lot of attention during the design phase was paid to improving and facilitating later assembly. There is not one part which is difficult to hold or to fix in place when assembling the movement, not one wire spring which needs to be installed under tension and immediately makes the watchmaker utter his desire for a third hand. The parts almost fall into place; such as the automatic winding train, which is created as a module and can be detached completely as a single unit. The finish of the functional parts seems to be very good, including the polishing of pinion leaves, the carefully rounded and polished escape wheel teeth, the clean and precisely cut wheels. Most of the flat steel parts like the click spring, intermediate crown wheel rocker, setting wheel rocker and automatic winding springs are stamped out parts with a rather industrial finish (detail pictures 4,5).
One exception is the nicely finished adjustable stud carrier: this part comes with a nice straight grained surface and chamfered as well as polished bevels which are well executed and represent the classic approach to steel parts finish. The plain screws are nicely polished and without cause for complaint, as are the traditionally heat blued screws.
The decorative finish of plates and bridges is difficult to characterize; maybe "post modern" would fit the bill. At first sight, there seems to be rather traditional decoration: circular Geneva stripes on the rotor and bridges, nice perlage on the mainplate, the very nicely contrasting massive gold rotor weight and the blued screws. But on a closer inspection, caliber 975 is missing many of the finer forms of decoration: beveling (or "anglage") of plates and bridges is in fact simply nonexistent, and is replaced by rounded, uniformly matte surface edges. Jewel counter sinks are generally minimal, and those for the screw heads are replaced by large simple matte finished recesses (detail pictures 7,8).
(Editor's note: We should remember that "this caliber can be bought in a
Master Hometime at euros 5,000." As a
manufacturer, certain business decisions must be made - "you have to make a consensus and cannot expect the finishing of a
limited edition priced at 50k euros or more.")
Over all, in my eyes caliber 975 represents a rather successful execution of a traditionally dressed, but industrial finish. As much as I like the technical design and conception, I'd love to see a "luxury" version with a little bit more traditional finish. I'm sure it would be a stunning movement, some springs made from a thicker base material and nicely chamfered, instead using parts stamped out and bent from a thin sheet. A nice anglage with sharp and precise transitions, polished jewel and screw head counter sinks would add a great deal. And if one may be allowed to dream, then yes, a Breguet overcoil would be appreciated as well.
Comments, suggestions, and corrections to this article are
Copyright February 2005 - Suitbert Walter and ThePuristS.com - all rights reserved