21 years: 2005 - 2026

Blog: Stop Work and Recoiling Clicks

Date: 30 July 2015

Copyright © David Boettcher 2005 - 2026 all rights reserved.

I make additions and corrections to this web site frequently, but because they are buried somewhere on one of the pages the changes are not very noticeable, so I decided to create this blog section to highlight new material. Here below you will find part of one of the pages that I have either changed or added to significantly.

The section below about stop work and recoiling clicks, and an often repeated myth about the purpose of stop work, is from my page about watch movements.

If you have any questions or comments, please don't hesitate to contact me via my Contact Me page.

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Stop Work and Recoiling Clicks

Stop work limits the range of winding of a watch mainspring, in particular the degree to which the mainspring can be wound up. In a watch with a fusee, this is necessary to stop the fusee chain riding out of the groove at the top of the fusee cone. In a watch with a going barrel, it is used to prevent the excessive force that could be locked in at the end of winding when the spring cannot be wound any further.

A mechanical watch is driven by the power stored in a spring. This is called the main spring or mainspring to distinguish it from other springs in the movement, in particular the balance spring.

The mainspring is contained in a barrel with its inner end fixed to a central shaft called the barrel arbor. The outer end of the mainspring is fixed to the inner wall of the barrel. When it is wound up, the mainspring exerts a torque or turning force between the arbor and barrel. The arbor is prevented from turning by a ratchet, so the torque drives the watch train and escapement, making the watch run.

In almost all modern watches, the mainspring barrel has teeth on its outside, which drive the movement directly, and is called a going barrel. Some watches and clocks have a fusee, a cone shaped device that evens out the torque of the mainspring. In a watch or clock with a fusee, the mainspring drives the fusee through a chain, and the fusee drives the movement.

The ratchet allows the barrel arbor to turn in only one direction. This is used when winding a watch. Winding turns the arbor, causing the spring to wrap tighter around the arbor, increasing the energy stored in the spring and the turning force on the barrel. The ratchet stops the arbor from turning backwards when winding is finished.

When the mainspring is fully wound, any further turning force cannot be absorbed by the spring and instead goes directly into driving the train. If force continues to be applied to the winding mechanism, this is transmitted directly to the wheel train and the escapement, producing excessive balance amplitude which can damage the escapement. For this reason, you should stop winding a mechanical watch as soon as the sharp increase of resistance is felt at the end of winding, when the spring is fully wound.

The torque exerted by a mainspring is not constant as the spring unwinds. In the middle part of its range it closely follows Hooke's law; the torque is proportional the angle of rotation of the barrel. But at the extremes, when the spring is either tightly wound around the mainspring barrel arbor, or almost fully uncoiled so that it is resting against the barrel wall, the variation is no longer linear as shown in the diagram here, due the way the spring is attached to the barrel and arbor.

If the spring is wound fully and tightly around its arbor, the very high torque that this creates can cause the balance to turn further than it should and the impulse pin to strike the outside of the lever fork. This not only results in inaccurate timekeeping but can also damage the escapement. To prevent this, either ‘stop work’ is used to stop the mainspring being wound tightly around its arbor, or a recoiling click is used to back off the mainspring a little before damaging amplitude can build up.

To avoid the very low torque when the spring is near fully unwound, when the frequency of the balance would be affected, the spring is sized so that a manually wound watch will go for around 36 hours, on the assumption that the owner will wind it every 24 hours and hence the last portion of the unwinding outside the optimum operating range will not be encountered in normal use.

There is a common misunderstanding about stop work. It is often said that its purpose is to limit the operating range of the spring to its middle part, or to prevent the spring from unwinding beyond a point where its increasing weakness causes the watch to lose accuracy. This is not correct, but it is often repeated and needs to be discussed, so I have included a discussion at the end of this section in Myth About Stop Work

Maltese Cross or Geneva Stop Work

Maltese cross, or Geneva, stop work limits the turning of the spring barrel so that the very high torque caused when the mainspring is wound tightly around its arbor at the end of winding is avoided. The picture here shows the general arrangement, the part to the right is supposed to resemble a Maltese cross, which is where the device gets its name from.

The piece with the projecting finger sits on a square section of the arbor so that it must rotate with it. The piece shaped vaguely like a Maltese cross is attached to the spring barrel by a shouldered screw and is free to rotate. As the spring is wound and the arbor rotates relative to the spring barrel, the finger engages with each of the slots in turn and turns the cross. One of the arms of the cross is wider than the others and when this is encountered it locks against the finger piece on the barrel arbor, as is shown in the picture, preventing the spring barrel from turning any further.

The same thing happens in reverse as the spring unwinds, the finger piece turns the cross until the wide arm is reached in the opposite direction and further rotation is blocked. At this point the spring barrel can turn no further and the watch will stop. This is the source of the myth discussed below, that the purpose of stop work is to prevent the watch using a weak part of the spring that would make timekeeping less accurate. However, this is a feature of the way the stop work operates; it is not its main purpose, which is to prevent the mainspring from being wound too tight.

The stop work patented by IWC in 1904 in Swiss patent CH 31457 Dispositif pour limiter le remontage des mouvements d'horlogerie à barillet, or device for limiting the winding of a watch movement barrel, is a variation of this type of stop work called ‘geared stop work’. Instead of the Maltese cross and finger piece, which allow only a small range of adjustments to the operation of the stop work, gears are used. This allows the number of turns that the barrel can make before it is stopped to be varied, and allows finer adjustment of the exact point in winding at which the stop operates when the spring is being wound. Rather strangely I have never seen the IWC patented stop work, all IWC watches with stop work seem to have conventional Maltese cross stop work.

Recoil Clicks

The function of stop work with a going barrel was to prevent excessive force from the mainspring when it was fully wound. Stop work prevented the spring from being fully wound, but was a complicated way of achieving it, and it also stopped the watch if the owner was late in winding it. The invention of the recoiling click, which allowed the mainspring barrel to reverse slightly after the spring was fully wound, achieved the same end with much less complication and cost.

In watchmaking terms a click is a pawl that lets a toothed or ratchet wheel turn in one direction but blocks it from turning in the other direction. A recoil click in the keyless work is designed so that when the mainspring is fully wound, the click allows the barrel to turn backwards slightly, to "recoil", and let the mainspring uncoil a little from being fully wound. This removes the sharp increase in torque shown at the right hand side of the graph at the 100% wound position.

In 1877, Charles Haseler, of Aston, near Birmingham, who probably worked for the English Watch Company, was awarded a patent for a recoiling click. Haseler explained that in a going barrels without stop-work, when the mainspring is wound up to its full extent, it is in ‘a state of extreme tension’ until the spring hss slightly relaxed. The solution was to make the pivot hole in the click elongated so that when winding is finished, the pawl can slide backwards, allowing the barrel to turn a little, relieving the extreme tension.

High quality watches continued to be fitted with stop work; not because it improved timekeeping but because stop work was expected on a high qulity watch. In 1881, Henry Ganney, a member of the British Horological Institute and forthright commentator on horological matters, reported,

Noticing the absence of stop-work from Mr. Guye's second quality work, I was told they only put it to their best work in deference to general prejudice on the stop-work question ; but as a matter of fact the watches kept a better rate without stop-work, as fewer main-springs broke, as the extra width obtained by the suppression of the stop-work gave a strength and elasticity unobtainable otherwise. With such testimony it is useless to contend, and the sooner watch buyers and wearers are enlightened on the subject the better, and with the stop-work will disappear a cause of much trouble to repairers.

Automatic Winding

Automatic watches, which are constantly being wound while they are worn, have a mainspring that is designed to slip in the spring barrel when it is fully wound to avoid over straining the winding mechanism. The grease used has to be the correct grease to allow just the right amount of slippage. If the grease dries out and the spring can't slip, then the automatic winding mechanism can damage itself or the barrel; another good reason for getting a watch serviced regularly.

Myth About Going Barrel Stop Work

There is a common misunderstanding about the purpose of stop work used with a going barrel such as the Maltese Cross or Geneva mechanism. It is often said that its purpose is to limit the operating range of the spring to its middle part, to prevent the spring from unwinding beyond a point where it becomes too weak and causes the watch to loose accuracy. This is not correct.

Although the effect of stop work is to limit the operating range of the spring to its middle part, this is not its purpose. The fact that stop work prevents the mainspring of a going barrel from fully unwinding is an unwanted consequence of the design that is a nuisance and provides no benefit.

The principal purpose of stop work is to prevent the barrel being further wound at the end of winding. This is to avoid the high torque caused when the mainspring is wound tightly around its arbor. But of course, by limiting the number of turns the barrel can make, the stop work will stop the barrel turning before the spring is fully unwound, thereby stopping the watch. This is a consequence of the design rather than its primary purpose.

Rather than preventing a loss of accuracy, stopping a watch results in a total loss of accuracy, which is an inconvenience and annoyance to the owner.

As the mainspring of a going barrel (i.e. no fusee) unwinds, its torque reduces and the amplitude of the balance also reduces. With a manually wound watch this usually happens every 24 hours, between when it is fully wound and when it is run down before it is next fully wound. The effect of this variation in amplitude between fully wound and run down on timekeeping is minimised by making the balance and balance spring assembly as near to "isochronous" as possible, within the normal operating range of the mainspring.

Although a watch maintains its rate less accurately, and therefore keeps time less well, if it operates with the spring run down so that it is outside the range for which the balance is isochronal, the watch is still of some use to its owner. It might lose a few minutes, but it can be wound and corrected to time when the opportunity presents itself. However, a watch that has stopped has totally lost accuracy and is useless.

A stopped watch is of no use to its owner whatsoever. In fact is a positive nuisance because, in addition to winding it, the owner must then find a reference time to set the it correctly against. Today this is easy, but in earlier times, when stop work was common, it was not so easy to find a clock or a sundial.

In case this discussion does not convince, I quote George Daniels (Watchmaking, p284) ‘If the barrel is without stop work, then some form of resilient or recoiling pawl is necessary to relieve the pressure of the fully wound spring.’ Also, in Britten (Watch & Clockmaker's Handbook, 16th edition, p38), ‘To avoid high torque when the mainspring is tight wound about its arbor, various stop work devices can be used.’

In the Horological Journal June 1884, T. D. Wright wrote ‘The Winding of Watches. I have had a number of high-priced American watches through my hands, and have been surprised to find in every case that the barrel had no stop-work. There are some advantages gained in having no stop at the “down” position, because if a wearer forgets to wind his watch at the usual time, it will go many hours longer ; but every good watch should have a stop to prevent excessive winding up.’ These watches were fitted with recoiling clicks, American watchmakers finding no benefit to timekeeping of more complicated stop work.