The following article was written by Paul J. Chambre, who has
posted frequently to the
TimeZone Vintage Forum.
Paul has been gracious enough to allow me to host his article
here. Thanks Paul!
Forgotten Masterpieces: The Last Elgins
Around 1958 Elgin introduced a pair of notable advancements for their higher end watches, these were the Durabalance free-sprung balance, and the calibers 760 and 761, the only American made self-winding movements. These last great achievements of what was at one time the worlds largest watch company were unfortunately not enough to save the manufacturer. The Elgin National Watch Company was to last only five years after their introduction. These late Elgins offer an interesting challenge for collectors. With a few exceptions, they are not particularly rare, and the prices are generally low, but parts for watches of the late Elgin years are scarce indeed. So, why should a collector bother? I'll try to answer that.
The durabalance (illustrated at right) was Elgin's design for a free-sprung balance. A free-sprung balance is a balance that dispenses with the conventional regulator pins found in most mechanical movements.
In standard designs, the regulator pins are attached to the regulator itself, which sits on top of the balance bridge. The pins are suspended, one on either side of the hairspring. When the regulator is moved, the pins are moved either closer or farther from the stud at the end of the hairspring. Since the hairspring touches the regulator pins as it "breathes," the presence of these pins effectively shortens the hairspring. A shorter hairspring results in a shorter period for the balance to swing, and the watch therefore gains. By moving the regulator pins to the correct location, the effective length of the hairspring can be fine-tuned to eliminate minor timing errors. For various reasons, though, this method of regulation is not the most desirable.
Another method of fine-tuning the period of the balance is by changing its moment of inertia. Moment of inertia is a combination of the mass of the balance and the distance that mass is located from the hub. A high mass near the rim provides more moment of inertia than a high mass near the hub or a low mass near the rim. The higher the moment of inertia of the balance, the longer its period (all other things being equal.) One way to adjust moment of inertia is to add mass. Watchmakers often do this when regulating watches with screwed balances. Small washers can be added under the screws to increase the moment of inertia of the balance and therefore slow the watch. This would be a tedious method of accomplishing fine-regulation, though, as changing the washers takes time, and the watchmaker would need a very wide variety of washers. A second method of adjusting moment of inertia is to provide a mass that can be moved closer to or further from the hub. This method is used by Patek-Philippe in their Gyromax balance. The Gyromax uses C shaped weights around the rim. If the slot in the C is turned towards the hub, the moment of inertia of the balance is increased, as most of the mass of the weight will be near the rim. If the slot is turned outward, the moment of inertia is reduced. Other companies use similar methods, the most common being mean-time screws: large screws which can be adjusted in or out to vary the moment of inertia of the balance.
In the case of the Durabalance, Elgin developed a simple and elegant method of regulating the watch. The spiral arms of the balance carry two weights (b), held in place by a spring (c). If the spring is moved, it will cause the weights to follow the spiral arms and move either inward towards the hub, or out towards the rim. The effect will be a loss, or gain, of moment of inertia, respectively. A lighter or heavier pair of weights could be installed in watches that needed additional range. Since this design did not use the conventional regulator, it made manufacture, assembly, and service simpler.
Those spiral arms served an additional purpose as well; they allowed the bulk of the balance's mass, the rim, to be sprung relative to the staff. This protected the balance pivots from shocks, as, in the case of an impact, the rim would just bounce back and forth on the spiral arms. Elgin was so confident in this design, combined with sprung end stones, that they gave a lifetime guarantee on the balance staff in Durabalance watches. Watches bearing the Durabalance can be identified by the symbol shown under the Lord Elgin on the dial at right.
The Durabalance was used in the 760 and 761 automatics that I detail below, but it also found it's way into a number of other Elgin calibers. A smaller version was also developed for use in ladies watches. One notable watch to use the Durabalance was the B.W. Raymond wristwatch. This was the first wristwatch to gain railroad approval. The original model used a caliber 730A movement, later models contained a 780. Both calibers were 23 jewel, manual wind, hack movements. To further insure their reliability they were presented in screw back cases and had iron dials for magnetic shielding.
As can be seen from the picture at right, the 730A had the standard 17 jewels, plus caps on the bridge side of the escape, fourth, and third wheels. This accounts for 20 of the 23 jewels. The plate side of the pallet arbor and escape wheel were also capped, so there's two more. The 23rd jewel, though, is an interesting one; it is the post on which the minute wheel runs.
Besides the high jeweling, the B.W. Raymonds were also adjusted in six positions. The factory poising of 730A balance wheels is another topic of interest. Elgin would test completed 730A B.W. Raymonds on a special timing machine and then drill and time the balance in the watch. Service literature for 730A's suggests that if a balance should ever require repoising, the whole watch should be sent back to the factory.
The American Automatics:
Along with the 607 and 618, the Elgin 760 and 761 have the sad honor of being the only American made automatic movements. Even as they were being developed, other American companies were giving in to the Swiss dominance of the market. Hamilton adopted Swiss ebauches for its automatics; Waltham had tried that, but had already gone out of business in 1957, as Elgin audaciously pressed on.
As a completely independent design, these movements offer a number of innovations not seen at their time. They provided bi-directional, full-rotor winding, without sprung clutches. They also provided two different automatic winding gear ratios; it would switch between them as the mainspring gained tension. To reduce parts count, they integrated the manual and automatic winding trains. The mainspring click in these watches actually brakes the second automatic winding wheel, rather than the winding wheel on the barrel.
The jewel count in these movements is given as 27 for the 761 and 30 for the 760. Pictured at right is a 761, with and without its rotor. A count of the visible jewels, and standard assumptions about those not visible, would account for only 21 - so where are the other 6? The answer is one of the most elegant innovations in the watch.
The directional clutches for the automatic winding system are permanently attached to the rotor. Stacked on top of each other on the rotor post are two pinions. One spins freely clockwise but locks counter-clockwise, the other does the reverse. Within these two clutches are the missing six jewels (see diagram below.) In the diagram, as the rotor turns CCW, the cylindrical jewels bind in the narrow ends of their slots, causing the pinion to turn.
When the rotor turns CW, the jewels can roll freely in the open ends of the slots, and the pinion idles. The other pinion is the mirror image of this one. This clutch design had the major advantages of operating without lubrication and without noticeable wear.
As for the additional three jewels in the 760, these were in the form of caps at each end of the escape wheel, and a cap on the bridge end of the fourth wheel. The 760 was also more highly adjusted (six adjustments rather than the 761's "adj'd") and had a beat adjustment device on the balance bridge (picture at right.)
Another design decision that was unconventional in these movements was the use of an off-center center wheel. This allowed the automatic winding train to be set on the same level with the time train, providing for a thinner, more compact, movement. The 76x's measure just 26.1mm across and 5.9mm in thickness (to the top of the sweep pinion.)
Although it died when the doors closed, the people of the last years of the Elgin National Watch Company never gave up on their dream of high quality, innovative, watches designed and manufactured in the United States. It is sad to see that while company after company rediscovers its heritage of fine watchmaking in Germany, the once proud names in American watchmaking remain nothing but marketing symbols for the cheapest watches. As a collector, I deeply appreciate what the people of Elgin were trying to do, and hope they their efforts will be more valued in the future - both by those who collect the vintage pieces and by those who may once again build watches that can be marked American Made.
Copyright 1999 Paul J. Chambre, except diagram of Durabalance assembly copyright 1959 Elgin National Watch Company.