I initially prepared this as a contribution article to one of the more popular watch sites on the Internet, but the site owner decided to leave these technical articles to the real watch makers, not hobbyists. As such I decided to publish it here instead. This is something different from my usual writings, but I learnt a lot about this particular feature, somewhat more of a visual spectacle than real functionality.
All pictures taken from various sources from the Internet. Copyright remains with the original owners.
The swan neck regulator, alongside the three quarter plate is one of the hallmarks of German watch making.
Let’s take a deeper look into this device, its history, how it works and its uses in watches today.
The traditional balance and the balance wheel found in almost all watches today plays a central part in the timekeeping function of a watch, substituting the harmonic oscillation of a pendulum found in a standing clock, to one of a minuscule wheel swinging back and fro at regular intervals in order to keep time. It is these regular oscillations or “swings” that determine the rate (time gained or lost) of a watch.
In most watches using a curb pins and stud approach (i.e. excluding free sprung balance wheels), the rate of the watch movement is determined by the effective length of the balance spring. The balance spring (aka hairspring) is the very fine spring that you see coiled up within the circumference of the balance wheel. Shortening the effective length of balance spring causes the watch to run faster, and lengthening it causes it to slow down. This is explain in more detail later.
The effective length of the balance spring can be changed by simply adjusting the position of the curb pins, which holds between them a length of the end of the coiled hairspring. This position is adjusted by a device known as the “regulator”.
Most watches today uses a “Bosley” regulator or a design derived from it, which comprises of a circular portion that is centred on the balance wheel, with a long sharp end (commonly referred to as the regulator) that lies on the balance cock/bridge where one can normally see the letters F and S engraved on it and a short end where the curb pins holding one end of the balance spring are found. The “Bosley” regulator was patented in 1755 by Joseph Bosley.
Moving the long end of the regulator towards the F (S) engraving will move the curb pins further (nearer) from (to) the stud and correspondingly cause the effective length of the hairspring to shorten (lengthen) and correspondingly cause the watch to run faster (slower). Take note that the markings between F and S are for visual reference only and are usually not a accurate indicator of any scale of time gained/lost. The Bosley regulator is the basis of many of the modern regulators in use today such as the ETAchron regulator and Seiko’s tadpole regulator found in their higher end models.
One usually regulates the rate of the watch via the regulator with the aid of a timing machine. One point to note is that many watch enthusiasts confuse this action with “adjusting” a watch, when it really is just “regulating” a watch. “Adjusting” a watch comprises of a much wider range of actions than simply moving a small lever.
Reed’s Swan Neck Regulator
Some years later, the American watch maker George Reed patented a device (US Patent no. 61867) on February 5 1867, which is now known today as the Swan Neck regulator. To be fair, this was not in any way a replacement for the Bosley Regulator, but an enhancement to 1) fine tune the regulation and 2) ensure that the regulator stays in place once the desired rate has been achieved.
Refer to the images below for the original patent. PDF of his patents can be obtained from this link.
How it works
The basic concept of Reed’s idea was to have a curved piece of tensile metal (the swan neck) exerting a force against the regulator in one direction while having a screw on the opposite side of the regulator to exert an opposing force. The screw can be used to make fine adjustment of the regulator by screwing it inwards or outwards, pushing the regulator towards the desired position while ensuring that the regulator cannot be knocked astride by a hard knock or drop as the swan neck ensures it maintains its position against the screw.
Some companies have improved upon the Swan Neck Regulator, for example Muehle-Glashuette’s woodpecker regulator, which not only exerts a force on the regulator on the horizontal plane but also pushes it down onto the balance cock/bridge. You can read more about their technology here.
Some other companies have done away with regulators all together and instead rely on free sprung balance wheels with adjustable weights on the rim to regulate the rate of a watch. Famous examples include Rolex’s Microstella and Patek’s Gyromax.
Functionality vs Visual Spectacle
As discussed briefly above, the Swan Neck was first envisioned as a tool to allow for micro regulation of the rate of the watch but it gradually became a nice to have feature in more expensive time pieces, especially for the German marques. This is especially so in movements with double swan necks.
Certainly it is quite a spectacle and feast for the eyes, but one might wonder what a double swan neck is for when I have explained above that the swan neck is used for rate adjustment. Well, the second “swan neck” is used to adjust the beat error, the “ticks” and the “tocks” of a movement, which should differ by no more than 0.2ms. This is done by linking the second “swan neck” to the adjustable stud, not to the curb pins.
It is certainly up to the task, but it does lead one to wonder whether this has crossed the line from being functional to being a means of showcasing movement finishing as there are easier and cheaper means of achieving the same effect.
Similarly in cases where a swan neck is used in conjunction with a free sprung balance, the swan neck is used to manipulate the adjustable stud in order to control the beat error. The rate of the watch is still adjusted by the weights on the free sprung balance wheel.
In contrast to the rate of the watch, the beat (error) of the watch will need to be adjusted only on a very infrequent basis. To employ a swan neck regulator for such purposes smacks of nothing more than a superfluous intent to showcase the movement finishing/engraving (and at the same time provide yet another reason to charge consumers more).