Haven't actually got this one yet, but it is winging its way over already...
Lord Elgin with the (in)famous call 760 movement. Was fairly clean, so I decided to go for it:
Now, the first thing that really stands out is that "Made In America" at the 6. This is one of what is called "The Forgotten Masterpieces" that basically mark the end of the US watch industry as such. While watches are still made in the US, by companies such as Kobold, RMG and Mk II, as well as others, these are all basically specialty boutique watch makers, which means that they manufacture watches using Swiss movements (and yes, I know RMG uses Hamilton movements, but these are vintage pocket watch movements, and hence I don't count them...)
The real end for US manufacturers came in the 20 years after WW2 ended. By that time - 1965 - the last of the major US makers, Hamilton, had been purchased and watch manufacturing ended in the US, something that hasn't changed in the last 40+ years.
Why? Because there is no US industrial policy to support such manufacturing: it has been the industrial policy of the US, basically since the 1960s, not to have any industrial policy. I will leave it as an exercise to the reader to decide if this way a wise policy or not.
While I'd love to have the time to write a complete history of the American watch industry, I'm just going to cover this particular watch and its historical role. Most pictures are from the seller with his permission: others are from Ranfft or from various web sites over the years.
It's a standard 3-hand watch, externally, with gold markers for the hours and an internal train track for the minutes and seconds. The hands, especially the minutes hand, are perfectly sized, while the seconds hand is characteristically somewhat stubby: all images I've seen online with this dial design show this. There's only one other dial out there that I've seen, a silver-colored one, that uses a longer, more traditional seconds hand that goes out further, as you can see here:
Crown is original on this one as well:
So, what about this "Forgotten Masterpiece?" Why is it called that?
Here's a shot of the movement...
It's not in the best of shape - there's a fair amount of grime I'll have to remove - but what makes the watch a forgotten masterpiece (not my term, but rather from this Elgin site) is the movement, which despite the fairly mundane nature of the finishing is truly unique: the Durabalance and the winding mechanism.
The Durabalance can be seen here:
What makes the Durabalance so unique?
First of all, it's American designed and made, and was highly innovative.
Second of all, it's a free-sprung balance, without the conventional regulator pins. Now, I'm gonna get all watchgeeky on y'all and talk about what that means.
Normally, the balance spring is held by regulator pins, attached to the regulator. These pins are suspended on each side of the hairspring and the watch is regulated by moving the pins one way or another from the hairspring stud, effectively shortening (or lengthening, depending on how the watch is regulated) the length of the hairspring and hence changing the swing period of the balance during both upswing and downswing in the balance cycle. A shorter swing period will decrease the time between ticks, speeding up the watch; a longer swing increases the time between ticks, slowing the watch. This way of regulating a watch can eliminate minor timing errors (ca 20 seconds in either direction) and has the virtue of being fairly simple to manufacture, especially in large volumes, but does have disadvantages.
First and foremost, the hairspring of a watch is always a finely tuned piece of metal: clamping it down like this affects the isochronism of the movement in several ways. First of all, the hairspring should be ideally perfectly concentric, with no distortions for a truly smooth movement for both upswing and downswing; distorting this shape means the hairspring will always be distorted, and due to the distortion being geometry-dependent, the distortion has different effects in different positions. The hairspring is the core of the way the watch works: the spring obeys Hooke's Law (i.e. the extension of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit of the material) and the restoring torque of the spring is proportional to the angular displacement: a watch is isochronic when the period of oscillation is independent of the amplitude of the oscillation. If the center of gravity of the balance spring coincides with the axis of the hairspring, the hairspring assembly is isochronous.
To understand the importance of this, consider what the hairspring represents to the working of the watch: it is a harmonic oscillator, with the balance spring providing the force needed to reverse the cycle from uptick to downtick. The hairspring power curve is one of a sinusoidal motion of constant period, one whose resonance period is fairly immune to external influences, but also one that is highly dependent on that sinusoidal motion being as smooth and free of distortion as possible.
Mathematically, it is expressed as (sorry for the poor formatting):
T= 2 pi times the square root of (I / k)
where T=time, I = inertia of the balance wheel in kg/m^2 and k = spring coefficient (aka "stiffness") in nm/radian. The important thing is hence both I and k; both must be perfectly matched in order to achieve an absolutely smooth, consistent and repeatable period, aka T or time.
Second, regulators are friction fitted, clamped onto the hairspring, and even a simple knock can dislodge this under unfavorable conditions, meaning that the regulators will at the very least move from the original timed settings, and may actually drift, depending on both position and time. Third, and this is where the watchmakers get grey hair, positional adjustment becomes a game of finding the position of least worst accuracy, rather than a way of fine-tuning the movement's upswings and downswings in various positions.
These three reasons are the basic reasons why free-sprung balances, without a regulator assembly, are invariably used for high-end watches. The downside of using free-sprung balances are significantly higher costs, significantly tighter manufacturing specifications (why use a free-sprung balance when the rest of the watch is so sloppy as to negate the advantages?) and generally speaking are much more demanding to work on: getting a freely-sprung balance to sit up and sing requires a very good watchmaker indeed, one who can handle how free-sprung balances are adjusted.
Now, as most engineers will tell you, the best way to resolve a subassembly problem is to eliminate the subassembly entirely. Hence if you want to eliminate the regulator problems, get rid of the regulator.
Let's skip all the problems that arise with the balance wheel itself for the time being: let's simply talk about how to get the center of gravity of the hairspring into coincidence with the axis of the balance wheel (this is hard enough!). You do this by adjusting the balance of the balance wheel itself: the hairspring, when freely sprung, is a constant, after all, and can't be varied any more. While there are various means of doing this, including the removal of metal, the most elegant way of handling this way to place two small screws, diametrically opposed, usually in-line with balance spokes, that could be adjusted to bring the axis of the balance into unity with the center of gravity of the hairspring.
A free-sprung balance could hence breath (cycle concentrically) without distortion of any kind except gravity: this results in significantly better performance regardless of position, and other problems - such as shocks, drift of the mainspring power curve and/or lubrication - would show up as such, rather than being masked by the hairspring.
So where's the downside? It's a lot of work to properly regulate a balance with timing screws, and these must be made with a high degree of precision with very durable materials, since any loose play here makes a mockery of the whole idea. Companies like Patek, Rolex, Omega and others have found their own solutions to this tedious work, but I think one of the most elegant solutions is the one used by Elgin here.
The balance wheel itself - with the long spiral-shaped arms - is perfectly poised at the factory and remains so as long as the balance wheel remains intact. The weights are attached to the spiral arms and can only be moved in such a way that they always remain equidistant: in other words, the amplitude can be changed to compensate for aging components and wear, but the isochronism is only dependent on the physical integrity of the balance wheel assembly.
Which makes it totally cool: given an inital proper assembly and installation, a watchmaker can adjust the timing simply by moving a single weight, which automagically moves the other weight in the opposite direction, and you're done. Any other method requires the balance assembly to be removed and balanced: Elgin recommended that any adjustments to the balance wheel assembly be done with the watch movement installed in the watch.
In other words, this movement is in many ways a dream movement: it is designed to be timed in the case, under real-world conditions, yet be free-sprung and hence highly accurate under all operating conditions. Elegant!
There was an additional plus to this design: given the long spiral arms, the rim, where the mass and hence the inertia of the balance wheel is centered, is also sprung relative to the axis of the balance wheel, providing additional shock resistance to the movement by design.
To give you an idea of what this design did for accuracy, it was first used in the cal 730A movement, which was the first (and as far as I know, the only mechanical wristwatch to meet railroad accuracy standards and hence win approval. For those who know their railroad standards, that is one heck of an accomplishment.
The second unque aspect of this movement is the winding mechanism, which is more than slightly outrageous for its time. First of all, it is bidirectional, but doesn't use any sprung clutches, which were at that point notoriously hard to maintain. That in itself isn't bad, but Elgin also provided two different winding ratios and adjusted them automatically during the winding process of the mainspring!
Both manual and automatic winding were integrated to reduce part count: the directional clutches were attached directly to the rotor. There are two pinions on the rotor post, stacked on top of each other, with one spinning freely clockwise, the other counter-clockwise, both locking in the opposite direction. In each of these clutches are three jewels (total six): as the rotor turns in one direction, the cylindrical jewels in one clutch bind, causing the pinion to turn; moving in the other direction, the jewels release, but the other pinion binds. Given that there is no point friction in the winding system and that surface friction between jewel and metal is minimal, the winding system didn't need lubrication, and given hardened surfaces of the metal, there was no wear. Seriously intelligent and cool.
Given the fact that the movement started out fully jeweled (21 jewels), after adding 6 for the winding mechanism, where are the other three?
The escape wheel as capped on both ends, as well as a cap on the bridge end of the fourth wheel. While perhaps (okay, more than perhaps) overkill in terms of real efficiency, the jewel count of 30 does not include any "play" jewels that serve no purpose.
The movement size is also surprisingly small, given everything going on: 26.1mm across and only 5.9mm thick to the top of the central sweep second pinion. This was achieved via an off-center center wheel (wait: if a center wheel is off-center, is it still a center wheel, or is it an off-center wheel? ), which allowed the winding train to be on the same level as the gear train. This is vastly more elegant that the usual toss-on-the-top winding mechanisms of modern automatic movements...
I'll post more on this when I actually get the watch...