About Watch MovementsCopyright © David Boettcher 2006 - 2017 all rights reserved.
I have split the old page about watch movements into two. This page is intended to convey some basic information about the movements (the "works") of mechanical or "wind up" watches. It gives some basic terms for the parts of a movement so that you can ask questions about them more confidently, and it gives some advice on caring for a mechanical watch.
The effects of temperature on the rate of a watch and attempts to compensate for this are such a large topic that I have made a separate page about temperature effects.
If you have any questions or comments, please don't hesitate to contact me via my Contact me page.
Lever escapement movement
The picture here of a movement with a lever escapement should help with some basic terms for the parts of a movement which you can see when you open the case back. If you click on it a larger version should open in a pop-up window where you can see more detail. If your movement doesn't have the escape wheel pivot visible like this one it might have a cylinder escapement, see cylinder escapement further down this page.
I have indicated where the winding stem enters the movement at the top of the picture. The stem carries a pinion which meshes with the crown wheel. When the stem is turned, the pinion turns the crown wheel, which turns the ratchet wheel connected to the mainspring arbor, winding the spring that makes the watch go. The spring is contained within a barrel underneath the ratchet wheel.
The mainspring barrel has a gear on its outside which drives the pinion of the centre wheel directly, this is called a going barrel. The centre wheel turns once per hour and its arbor is extended through the bottom plate and turns the minute hand, and it also turns the hour hand through a 12:1 reduction gearing called the motion work. Every time the minute hand makes one revolution the hour hand makes 1/12 of a revolution, so one complete revolution of the hour hand takes 12 hours.
The centre wheel drives the pinion of the third wheel, and the third wheel drives the pinion of the fourth wheel, the speed of rotation increasing each time. The fourth wheel is usually arranged to make one turn every minute. Its pivot in the bottom plate is often extended so that it passes through the dial where it turns a seconds hand. Watches with the "traditional" layout of the one shown here rarely have centre seconds hands - see below for more details of watches with centre seconds dials.
The fourth wheel also drives the pinion of the escape wheel. In a lever escapement movement like the one pictured, the escape wheel is locked by a lever pallet, which you should just about be able to see if you click on the picture to get the larger version. The pallets are either side of the lever pivot which I have labelled, they are tiny pale ruby coloured things, one is just visible above the screw on the rim of the balance.
The balance and its spring form the oscillator that controls the timekeeping of the watch. The balance has a central spoke that is mounted in the balance staff and carries a circular rim that is the oscillating mass. The balance spring is mounted above the balance. It is secured to the balance cock at its outer end by the stud. Its inner end is secured to the balance staff by the collet. The balance spring tries to hold the balance in one central position. If the balance is moved from that central position in either direction, the spring pulls it back. Like all masses on springs, the balance swings through the central position to the other side, and the spring then pulls it back from there.
As the balance swings back and forth, a small pin called the impulse pin or impulse jewel knocks the lever from one side to the other. Each time this happens, whichever pallet is currently locking the escape wheel releases and allows one tooth of the escape wheel to escape. The other pallet then catches the escape wheel and locks it, so that each time the balance swings, the escape wheel advances one tooth. Immediately after the locking pallet has released a tooth of the escape wheel, the escape wheel gives the pallet a push, which in turn makes the lever give a push to the balance through the impulse pin. This little push, or impulse as it is called, is what keeps the balance swinging backwards and forwards.
Once the balance has knocked the lever it carries on turning as far as its momentum and the little extra push it received from unlocking the escape wheel will take it against the resistance of the balance spring. When the balance has run out of energy it stops and then the balance spring accelerates it in the reverse direction. In passing it knocks the lever back the other way, and the sequence starts all over again.
The balance is so called because in early clocks there was no circular rim. The balance was a single central spoke or bar with weights hanging from it to provide the mass. These weights were moved to control the time keeping, and the whole thing looked like a weighing balance and hence the name. Some people call the balance a "balance wheel" but this is incorrect. In watch work, wheels have teeth on their rims which engage with pinions. The balance does not have teeth on its rim and so it is not a wheel. Britten's Watch and clockmaker's handbook, dictionary and guide 14th ed, 1938, makes it clear that balance wheel was the wheel next to the balance in a verge clock, i.e. it was an alternative term for the escape wheel.
Early watch movements have two plates, and most of the "works" sits between these. The bottom plate is the one behind the dial, the top plate is the one you see when you open the back of the watch. Early "full plate" watches have all the train wheels between the two full circular plates, with the balance and its cock mounted outside the plates on the top plate. To make movements thinner, part of the top plate was cut away so that the balance could be brought in between the two plates with its cock mounted on the bottom plate. These are "three-quarter plate" movements, where the top plate carries the pivots of the barrel, centre, third and fourth wheels. The next step was the "half plate movement" where the fourth wheel was pivoted in a separate cock and the plate carries the pivots of the barrel, centre and third wheels. Movements such as the one illustrated here, where bridges and cocks are used instead of a top plate, are called "Geneva" or "bar" movements. A bridge has a support and screw at each end, a cock has just one support and screw, so it is a cantilever and must be short to be sufficiently rigid.
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By far the commonest questions I get asked is "what do the letters on the movement A.R.F.S or F.S.A.R (or sometimes just FS or AR) mean?".
These letters are found on the balance cock under the regulator lever. They stand for "Faster Slower" and the same in French "Avance Retard" They show which way to move the regulator lever to make the watch go faster or slower.
The balance and its spring, called the "balance spring" or "hairspring", are the heart of a watch movement. The balance is the little flywheel that you see swinging backwards and forwards when you look at a watch movement that is running. The balance spring or hairspring is a fine spring that is fixed at its outer end to the balance cock and at its inner end to the balance staff, the arbor on which the balance is mounted.
The balance and its spring form a simple harmonic oscillator that oscillates with a constant frequency and controls the rate at which the watch runs and determine its timekeeping.
ARFS on a watch regulator
The frequency of oscillation of the balance is usually expressed by watchmakers in "vibrations". A vibration is the same as one tick, the click made when one tooth of the escape wheel "escapes" and the whole train moves forward one step. The escapement makes one tick when the balance swings one way, and another when it swings back. Each tick is half of a complete oscillation expressed in Hertz (Hz), the number of complete oscillations it makes in one second. A typical watch from the early twentieth century, has a balance frequency of 18,000 vibrations per hour, or 18,000 vph. This is five vibrations per second, or 2.5 Hz. Some more modern watches have faster trains, 21,000 vph or even 36,000 vph, in an attempt to improve their timekeeping.
The frequency at which the balance oscillates is determined by its rotational inertia and the strength of the balance spring. Think of a weight hanging from a spring. If you pull it down and let go, it will oscillate up and down at a certain frequency. The balance and its spring work in exactly the same way, but in rotation rather than up and down.
The rotational inertia of the balance is dominated by the mass of the rim, which is not easy to change. The strength of the balance spring is determined by its cross section and its length. The cross section of the spring is even more difficult to change than the mass of the balance. But the effective length of the balance spring can easily be altered, and this allows the rate of the watch to be easily adjusted.
In a watch with a regulator the effective length of the balance spring is determined by two curb pins, one on each side of the outer coil of the balance spring close to where it is fixed to the balance cock by the stud. The curb pins hold the balance spring lightly so that the piece of spring between the stud and the curb pins is "dead" and has no effect on the frequency of the balance. The effective length of the balance spring, the length that determines the rate of the watch, is the free part on the other side of the curb pins, the spiral coil that terminates in the collet on the balance staff. The curb pins are moved along the outer coil of the balance spring by a regulator, make the effective length of the spring either longer or shorter. This changes the rate of the watch; an effectively longer balance spring causing it to run slower, a shorter one to run faster.
The type of regulator shown in the first photograph is called a Bosley regulator. The regulator lever is mounted on the balance cock, it has a circular centre section that is held in place by the upper cap jewel setting so that the lever turns co-axially with the balance staff. The short end of the lever carries the two curb pins which project downwards and embrace the outer coil of the balance spring. The long end of the lever projects over a graduated scale which is there for visual reference only, it is not calibrated. The letters A.R.F.S or F.S.A.R show which way to move the regulator lever to make the watch go faster or slower.
The Bosley regulator
The type of regulator with just a simple straight lever, the type shown in the first photograph above, was invented and patented in 1755 by Joseph Bosley, and is hence called a "Bosley regulator". It formed the basis for almost every regulator design that followed.
The photograph here shows am earlier form of Bosley regulator. This one is on a nineteenth century English pocket watch with a fusee movement and lever escapement.
The Bosley regulator lever has a circular section that is held in place on the balance cock by the upper cap jewel setting so that the lever turns co-axially with the balance staff. The under side of the lever carries the two curb pins, which are not visible in the photograph, that project downwards and embrace the outer coil of the balance spring. The long end of the lever projects over a graduated scale which is there for visual reference only, it is not calibrated. The scale of this watch is made from sterling silver. The end of the lever projects past the scale so that it can be moved with a finger nail. Fast and Slow are engraved on the plate to show which way to move the regulator lever to make the watch go faster or slower.
What the regulator can tell you
The ideal position for a regulator lever is in the centre of the scale. This looks best and also allows for small adjustments to rate either way. When the watch left the factory the regulator lever would have been close to the centre of the scale, and some watch repairers will make small adjustments to the balance inertia by adding or removing timing washers to make the lever sit exactly in the middle of the scale.
Small offsets of the lever from the centre are of no great consequence to the functioning of the watch, but if the regulator lever has to be excessively to one side or the other, or even off the scale, for the watch to keep good time, this tells you that something is wrong, most likely that the watch needs a service to replace old gummy oil with fresh new oil.
Omega regulator with snail cam adjuster
Which way to turn the regulator?
In the first picture above the letters A.R.F.S or F.S.A.R show which way to move the regulator lever to make the watch go faster or slower. It is easy to see that turning the regulator lever anti-clockwise towards the "R" and "S" indications for slower would move the curb pins towards the stud, making the free part of the balance spring longer and the watch run slower, and vice versa. Sometimes watches are fitted with additional complications that make it possible to achieve finer adjustments to the regulator, such as the regulator of an Omega pocket watch shown in the picture here which has a modified form of the Reed's regulator that is described further down on this page. In addition to the regulator lever there is a disc with a snail cam on it, and a spring that holds the bent tail of the lever against this snail.
Turning the disc rotates the snail cam which causes the lever to move, but at first glance the letters "F" and "S" might not show clearly which way to turn the cam. This is easy to work out by remembering that moving the curb pins towards the stud makes the free part of the balance spring longer and the watch run slower, and moving the curb pins away from the stud has the opposite effect. Looking at the red arrows in the picture you can see that turning the adjuster counter-clockwise towards the "F" causes the snail cam to move the regulator lever towards the spring, which moves the curb pins away from the stud, making the effective length of the balance spring shorter and the watch run faster. The marks on the disc are simply there for visual reference, they are not calibrated and variations in timing are done by experiment, moving the lever slightly and seeing how much effect this has on the timekeeping, usually with the aid of a timing machine.
Reed's Whiplash Regulator
In 1867 the American George P. Reed invented and patented an improvement to the Bosley regulator, US patent No. 61,867 dated February 5, 1867. This was a precision adjuster for the regulator lever consisting of a spring curved around the lever to bias it in one direction, with a screw used to move the lever in the opposite direction against the spring. Reed's addition to the Bosley regulator allowed finer adjustment to the regulator than can be achieved by simply moving the index lever with a finger or the tip of a screwdriver.
Reed's whiplash regulator: US patent 61,867, 5 February 1867.
Reed's regulator with its spring and precision adjustment is today usually called a "swan's neck regulator" or swan neck device, because of the shape of the curved spring which is vaguely in the shape of a swan's neck. Sometimes it is called "Reed's whiplash regulator", the whiplash also referring to the shape of the spring. It should really be called something like "Bosley regulator with Reed's whiplash adjuster", but this is rather a mouthful and no doubt "swan's neck" or "Reed's regulator" is more acceptable.
Reed regulator on Electa movement
In the figure from Reed's patent reproduced here you can see the swan neck spring "d" which curves around the lever of the Bosley regulator, and the adjuster screw "e" which passes through a threaded hole in the end of the spring "c". Screw e is screwed in or out to regulate the watch. In practice the end of the spring "c" is usually made in the form of a block with locating pegs and a securing screw or screws.
Reed's regulator was first used on watches made by Edward Howard in the USA, and after the expiry of the patent was widely used by watch manufacturers in America, Switzerland and Germany. There were many other types of micro-adjuster devised by inventive minds over the years, but Reed's design was simple and elegant and is still used today, in either its original form such as the one shown here on an Electa movement, or in one of many variants such as the Omega version pictured above with a snail cam instead of an adjusting screw.
Tompion's or Thuret's regulator
This is probably the earliest form of watch regulator. Thomas Tompion made the first English watches to have a balance spring in 1675, as part of Robert Hooke's efforts to show that he had invented the balance spring. A watch made by Tompion and presented to King Charles II was inscribed "Robert Hooke invent. 1658. T. Tompion fecit, 1675". This watch is lost and the exact form of the balance spring is not known, but later Tompion watches have the form of regulator shown here, which as a consequence is often called Tompion's regulator.
Tompion's or Thuret's regulator
The regulator is in the form of a curved rack and pinion. One end of the rack carries two curb pins that embrace the spiral balance spring. Moving these curb pins along the balance spring alters its effective length and so the rate of the watch. The rack is moved by applying a key to a square projecting from the pinion and turning it. Turning the pinion clockwise will move the curb pins away from the stud and shorten the effective length of the spring, making the watch run faster. Turning the pinion counter-clockwise will move the curb pins towards the stud, making the effective length of the spring shorter and the watch run faster.
Usually you can't see the rack and pinion, but a silver disc mounted on the arbor of the pinion is visible, set into the top plate. This plate is engraved with arbitrary numbers that are helpful as a relative reference when making adjustments.
In fact, it seems that although Hooke had been working on applying springs to watch balances for some years, it was Christiaan Huygens of the Netherlands who first came up with the idea of using a spiral balance spring, and it seems that watches with spiral balance springs and the type of rack and pinion regulator shown here were made by Thuret in Paris for Huygens before than Tompion's watches, so this should really be called Thuret's regulator, but I doubt that this will happen!
Watches without regulators
Some watches don't have regulators. These are carefully adjusted at the factory and there is no easy way to change their rate. They are called "free sprung".
The benefit of an indexless or free sprung watch is that there are no regulator curb pins to interfere with the balance spring. It is very difficult to make a pair of curb pins grip the balance spring with exactly the right amount of force. Too tight and the spring will kink when the regulator is moved, too loose and the part of the spring between the regulator and the stud can flex, upsetting the consistency of the timekeeping.
In addition to the basic mechanical objections to the use of curb pins, there is also an aspect of balance spring regulators called "point of attachment errors". The isochronism of a balance spring regulator is affected by the relationship between the point where the balance spring is attached to the plate and where it is attached to the collet. For instance, the attachment points can be arranged so that the balance spring contains a whole number of turns in its spiral, 12 say, or a fractional number, 12¼ or 12½ for example. The point of attachment and number of turns of the balance spring affects the frequency of oscillation for different amplitudes of vibration, which inevitably occur when the watch is in different positions. A free sprung watch fixes the point of attachment so that this effect is controlled at the point of manufacture, but movable curb pins change the point of attachment and thus the rate in different positions.
Point of attachment error is important in very high precision timekeepers, but is not really of concern for everyday use where other effects such as the thickening of the oil over time dominate, so regulators continue to be fitted to mechanical watches. And with a bit of good engineering they provide a visual treat that free sprung watches lack.
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One common description by sellers is that a watch is not going because it has been "over wound". This is nonsense. It is like saying that a car won't start because the fuel tank is full of fuel. Don't believe stories that being over wound is a fault in itself, or that a watch will stop because it is over wound. Just like a car with a full tank of fuel that won't start, the reason the watch doesn't go is because there is something wrong with it. This might be something simple that is easy to fix, and it might be something serious that could be very expensive, or even impossible, to fix.
It is really quite difficult to damage a watch by winding it - unless you have a vice-like grip, muscles like a gorilla, and no sense of feeling. Watches are built to be worn by normal human beings, so when you are winding a watch and feel that the crown doesn't want to turn any more, then just stop winding. You can't actually stop a watch by "over winding" it — when the spring is fully wound and you let go of the crown, if there is nothing wrong with it the watch will start running.
If you have had a watch for a few years and it doesn't wind easily, varies in its timekeeping or stops unexpectedly, then it most likely needs a service. All mechanical watches need a service every few years to clean out old gummed up oil and replace it with fresh. You wouldn't run a car for years without changing the oil, would you?
However, if you are thinking about buying a watch and the seller describes it as overwound, then you need to be extremely cautious. The seller might actually believe that this is the problem, or they might be trying to hide the fact that there is something seriously wrong with the watch; caveat emptor, buyer beware.
If it was your watch and it stopped working, then you would know its history and whether you had done something to it, such as dropped it. But with an unknown watch you don't know what has happened to it in its lifetime. It may be that the watch has not been serviced and the oil has gummed up; a simple service would sort this out fairly cheaply. But it could also be that there is a more severe problem, such as a broken balance staff or some internal wear or damage. This would be more expensive to rectify, quite possibly much more expensive, and sometimes even impossible, to fix — or impossibly expensive.
Once you get to know a bit about watches you will be able to make a judgement on this. If the balance is swinging freely and doesn't wobble on its pivots, and there is no obvious damage, then you can be fairly sure that a service will sort out the problem. But if you are not confident in assessing this, it may be better to pass on until you have more experience.
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Servicing a watch
A watch needs to be cleaned and oiled every so often because the oils and greases used to lubricate the moving parts thicken then dry out. Oil or grease that is dried out cannot lubricate the moving surfaces adequately and they wear or, even worse, over time oil can mix with dust from the atmosphere to form a grinding paste that quickly wears parts. Spare parts for old watches are often no longer available, so a worn out part can mean that an old watch cannot be repaired economically.
Modern watches with fully sealed waterproof cases can go longer between services than older watches with less well sealed cases. Case joints that are not well sealed allows dust and fluff into the case. Fluff is a nuisance, but dust is worse because it can combine with oil to form a grinding paste that quickly wears components. Old watches with less than fully waterproof cases should be cleaned and oiled every three or four years, more modern watches with fully waterproof cases can go longer, five or six years, or even as much as ten years for watches with co-axial escapements.
If you wind up an old watch and it seems to be running OK, bear in mind that although the components inside the watch are very small and consequently delicate. Human muscles, and even a fully wound mainspring, can generate powerful forces that can damage delicate components — see the section below about damaged stem bearings to see the damage that winding a watch everyday can do if this mechanism is not adequately lubricated.
Watches will continue to run for a surprisingly long time without being serviced. But by continuing to run a watch that has not been serviced for a long time, you might be building up wear and damage inside the watch that you can't see. This will become apparent when eventually the watch stops, at which point the damage might be so bad that it cannot be repaired.
Replacement parts for old watches are usually no longer available. In theory all the parts can be made for a mechanical watch by a skilled watchmaker, but this is expensive and might not be economic. And some parts are easier to make than others - I wouldn't fancy trying to make a balance spring, and these are now getting in short supply for older watches — even stocks of some mainsprings are running down. And I still haven't repaired the damaged stem bearings shown in the section below. I know how to do it in theory; bore out and sleeve. But in practice, accurately boring and sleeving a a bearing in a wristwatch plate a few millimetres thick is not an easy operation without expensive equipment that most watch repairers don't have.
Remember that these old watches have survived through many years and events until now, and it is your responsibility to take care of them and make sure you pass them on in good working condition. A mechanical watch that is regularly serviced could still be working just as well in centuries from now as the day it left the factory; you can't say that about electrical or electronic watches.
Regular servicing is particularly important for old hand wound watches because
- The cases tend to be not very well sealed, especially if they are jointed (hinged), so fluff and dust can get in and mix with the oil form either a sort of gum that can stop the watch working, or worse, a grinding paste that wears the moving parts.
- The keyless work (the mechanism that winds the watch or sets the hands when you turn the crown) of a hand wound watch takes a lot of stress through being used every day, and can wear badly if not adequately lubricated - see the discussion about this in the section below, and the picture of a badly worn bearing.
There are two methods of cleaning and lubricating a movement:
- The first method places the complete movement in the cleaning machine through a wash and two rinses, the second rinse containing a lubricant, and that's it. There are two problems with this method. It seems to me that the cleaning fluid will not be able to clean difficult to reach places such as the jewel holes with the pivots in them, although I understand that the end or cap stones are removed before cleaning. These need to be cleaned thoroughly to remove congealed oil. Perhaps a powerful ultrasonic machine can do this. I am sure that a single, necessarily very fine, lubricant cannot be ideal for all the different duties of each part of the mechanism, from the fast moving but lightly loaded balance staff to the slow moving but heavily loaded keyless work. This method is certainly quick and cheap, but the downside is probably that it needs to be repeated more often than a full strip and oil.
- The second method, and the only valid one in my view although it is more expensive, is a full strip, clean and lubricate, where the movement is completely dismantled, the parts are cleaned and rinsed in a specialised watch cleaning fluids, each component then examined for cleanliness and further cleaned if required, e.g. the jewel holes are "pegged out", which means a sharpened piece of special wood is pushed into the hole to remove any last traces of dried gummy old oil, and the movement then reassembled with the correct lubricant applied where it is needed. I use at least four different lubricants depending on the duty of each component, ranging from a grease for the keyless work and barrel arbor pivots where there is high torque and low speed, through to a light oil for the pivots of the faster train wheels, and a thixotropic grease for the escape pallet faces. These specialised oils and greases are very expensive, the grease that is used only on the pallet faces works out at well over £100,000 per gallon! (fortunately I don't buy it by the gallon.)
Before committing your watch to be serviced it is always best to ask which method will be used, simply for the avoidance of doubt. I once purchased some equipment from a watchmaker who used to work for the principal jewellery retailer of a reasonable sized town and an Omega agent. He told me that he used the first method on Omega watches for many years. I was astonished. There is no doubt that a quick dunk like this will get a watch going, but the lubricant carried in the final rinse has to be very thin because it has to go everywhere in the movement without gumming it up, so it doesn't last very long, and it can't adequately lubricate bearings under heavy load such as in the keyless work for winding and setting. More wristwatches are scrapped because of worn out bearings in the keyless work than due to any other reason - see the section on keyless work below.
Badly worn stem bearing
Stem wound and set watches, that is the type of watch that you wind up by the crown and set the time by pulling crown out away from the case, incorporate a "keyless mechanism". It is called this because you don't need a separate watch key to wind or set the watch, hence the watch is keyless. The most common "shifting sleeve" form of keyless work was invented in 1845 by Adrien Philippe, who later joined the Geneva company of Patek to form Patek Philippe. You can read more about the various forms of keyless work at Keyless Work.
The action of turning the crown to wind the the watch or set the time is carried into the mechanism by a metal shaft called the "stem". When you pull the crown out to set the time, the stem is drawn out and the keyless work, a system of levers, disengages the winding mechanism and engages the time setting mechanism.
If a watch is manual winding, then it has to be wound every day to keep going. Although the stem winding keyless mechanism is a clever piece of design, the bearings are small and not jewelled. If a watch is not regularly serviced and grease in the stem bearings renewed they can wear heavily. It is not unusual that a watch that otherwise runs perfectly well becomes impossible to repair because of wear in the stem bearings and keyless work, so it pays to be aware of this potential problem.
Wear in the stem bearings is the Achilles heel of manually wound watches. Automatic watches that wind themselves as the wearer moves around do not suffer anything like as much from this problem, because the stem is only used occasionally.
The picture here shows the outer stem bearing in the bottom plate of a watch. It is very badly worn - the tops of the ridges standing up from the bearing surface give an idea of where the original surface was and how much wear has occurred. This degree of wear has almost certainly been caused by the wearer winding his watch while it was still on his wrist. Although it is possible to slide a finger between the crown and your wrist with the watch in place and turn the crown, this picture shows you why this is a very bad idea. Jamming the finger between the wrist and the crown causes excessive side force on the crown and the stem, which has to be carried by this bearing. And as you can see, the bearing is not adequate to withstand this treatment and wears badly.
The moral of this is: always take off your watch to wind it, try to avoid sideways force on the crown as far as possible, and also have the watch serviced regularly to get the stem bearings lubricated. If you wait until your watch stops running or you can no longer wind it, it might be too late!
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Jewels are used in watch movements to provide hard smooth bearing surfaces that reduce friction, resulting in smoother operation, lower power consumption and reduced wear. They enable the train to deliver power to the escapement more uniformly, allow a weaker and longer mainspring to be used which delivers more consistent torque, and prolong the life of the mechanism by protecting parts from wear.
The picture here shows a movement from a 1914 Borgel wristwatch. It has a typical Swiss straight line lever escapement but this movement has more than the standard 15 jewels. You can see the normal jewel holes fitted to the third and fourth wheels to the left and slightly above the centre. This movement is "jewelled to the centre" which means the centre wheel bearing, the one right in the centre, is also jewelled, bringing the count up to 17 jewels, and the escape wheel has cap jewels, you cans see the polished steel setting and its screw on the escape wheel cock, these add a further two jewels bringing the total to 19.
The subject of the design and use of jewel bearings is, rather surprisingly, little discussed in text books on watchmaking. Their cleaning and replacement is well covered in texts about watch servicing, but in texts devoted to the theory and design of watches, such as A L Rawlings "The science of clocks and watches" and George Daniels' "Watchmaking" they are hardly mentioned. I expected to find some discussion of the design aspects of their use; finish, tolerances, the appropriate type of jewel to use in each place, etc. Perhaps there is some superlative text that renders discussion unnecessary which I have yet to discover.
The first jewel bearings
Jewel watch bearings were originally made from real gem stones, rubies and diamonds, hence the name "jewel". On 1 May 1704 Nicolas Fatio de Duillier, a friend of Isaac Newton, and Peter and Jacob Debaufre, watchmakers of Church Street, Soho, London, were granted a patent for 14 years over the method of making jewel bearings by piercing rubies. On 11 December 1704 the Court of the Clockmaker's Company was informed that Facio and the Debaufres had petitioned the House of Commons for an Act for "the sole applying precious and more common stones in Clocks and Watches", and for extending the term of their patent. The Clockmakers' Company naturally objected to this, which appears to have been intended to give the patent holders sole rights to use jewels of any sort in clocks and watches.
English lever 1833 rose diamond endstone
The Clockmakers' Company produced evidence to a committee of the House of Commons of an old watch with the maker's name Ignatius Huggerford, that had a stone fixed in the cock and balance work, which was important in persuading the committee to recommend that the Bill be rejected, which it was in January 1705. This evidence was regarded by the Clockmaker's Company as so important that the Watch was purchased from its then owner, Henry Magson, for £2 10s and kept by the Master of the Company for use in the Company's defence in case the Patentees should commence any suit. Ten shillings was given to Mr William Scale who appeared before the committee to prove he had the watch before the date of the Patent, and that he sold it to Mr. Magson.
In the nineteenth century Huggeford's watch was examined by Mr E J Thompson, a member of the court of the Clockmaker's Company, who reported that " The movement is not in any sense jewelled, the verge holes being of brass. A piece of coloured glass or soft stone, fastened in a disc of silver and burnished into a sink in the steel cock, gives a fictitious appearance of jewelling." It appears that if Facio and the Debaufres had stuck to claiming a patent for piercing holes through jewels they would probably have been successful, but in extending the claim to any jewelling - "the sole applying precious and more common stones in Clocks and Watches", they had overreached themselves and their claim fell.
The picture here is of a balance staff endstone from an English lever watch dated by the hallmark in its case to 1833. The setting is blued steel. The jewel is a rose diamond, a hemispherical diamond with the curved upper part cut in triangular facets. This was purely for decoration, the working face of the stone was the flat base. The diamond was brazed to the steel setting and the two were polished on the underside together.
It is often said that watch jewelling was a jealously guarded secret among English watch makers, but the jewels were there to be seen by anyone who cared to look, and techniques for cutting and shaping jewels had been known for centuries, so it can hardly have been a great secret. It is more likely that the continental makers had difficulty getting hold of raw jewels because the principal sources of rubies were in Sri Lanka and Burma, and the trade between them and Europe was dominated by the British East India Company. When free trade opened up British import and export trade in the middle of the nineteenth century, Swiss manufacturers started buying raw jewels in quantities in London and mass producing watch jewels, with serious consequences for the English hand craft producers.
In evidence given in 1887 to the select committee of the House of Commons examining the Merchandise Marks Act (1862) Amendment Bill, Alfred Bedford, the General Manager in Europe of the Waltham Watch Company, said that jewels for Waltham watches were bought in the rough in London and cut there, and that some were finished in London and some in America. During peacetime America continued to import jewels, mainly from Switzerland, until the 1940s when it was recognised that jewel bearings were so important in modern precision instruments and timepieces vital to the war effort that American firms were encouraged to begin manufacturing jewels.
Electa catalogue 1914: click image to enlarge.
Copyright © The Gallet Group
Because of the difficulty of shaping and boring very hard materials such as diamond and ruby, they were at first used only for the bearings and endstones or cap jewels of the balance staff. However, the importance of jewel bearings in reducing friction and wear was soon appreciated - John Harrison's prize winning timepiece H4 which was made between 1755 and 1759 was extensively jewelled - and jewels became more widely used in other parts of the movement.
Natural and synthetic jewels
All of the jewels used in the nineteenth century and early years of the twentieth century were made from natural gem stones, in the main rubies and sapphires. In 1902 Auguste Verneuil invented a method of making synthetic or artificial rubies which were much cheaper than natural gem stones.
The picture here is a scan of a page from an Electa catalogue dated 1914. It's interesting that even the 7 jewel basic version had a Bréguet balance spring and temperature compensated balance. The red rubies seem to be rather expensive, presumably they were natural gem stones rather than the other "jewels" which were synthetic. The first three entries on the table are for an "0" sized movement, this would be a 13''' movement for a wristwatch - for more about these measurements see watch sizes. The columns of prices do not have headings but I guess that the first is Swiss Francs and the second is English shillings and pence. Before the Great War currencies were tied to gold, the "gold standard" and had been stable for a long time. I think that French, Belgian and Swiss Francs were all valued at 25 to the pound sterling, the dollar was at four dollars to one pound sterling, hence the old English slang of a "dollar" for a crown (five shillings) and, more commonly, half-a-dollar for a half crown (2/6 or 2 shillings and six pence).
The extra charge for an 0 size movement with 15 jewels and 17 jewels in chatons at 1 and 8 Swiss Francs repectively are shown as 10 pence (10d) and six shillings and six pence (6/6) which agrees with the exchange rate, there were 240 pence to the pound so 1 Franc would be 240/25 = 9.6 pence, or 10 pence in round money, and 8 Francs would be 8 * 240/25 = 76.8 pence, or 6 shillings (72 pence) and 4.8 pence, six shillings and sixpence in round money, the sixpence being a common coin at the time. The extra charge for 21 red rubies set in chatons is 41.50 Francs or 33/6. The Francs work out at 41.5 * 240/25 = 398.4 pence or 33 shillings and 2.4 pence; 33 shillings and sixpence in round money; one pound thirteen shillings and sixpence. This would be an enormous extra charge, wristwatches in ordinary silver cases were being retailed at only two pounds and six shillings to two pounds and 10 shillings at the time, I bet not many were made with red rubies! You can read more about Electa and Gallet on my Gallet and Electa page.
Variations in friction in the balance pivots are the most significant point at which timekeeping will be affected. The amount of energy lost to friction during each oscillation of the balance compared to the amount of energy stored in the balance and spring assembly determine its "Q" factor. The higher the ratio, the better the timekeeping. It is no coincidence that the balance staff pivots were the first to be jewelled.
Balance assembly - balance staff in green
The picture here shows in red the jewel holes and cap jewels for the balance staff. The pivots of the balance staff are made very fine, only a few hundredths of a millimetre in diameter, to reduce friction. In addition, the holes of the two jewel bearings that the pivots pass through are made with convex rather than parallel sides, so that the pivots only touch them over a short distance.
Jewelling does reduce the wear, and thereby prolongs the life of a watch, but it also increases cost. Starting at the balance with two hole bearings and two endstones (jewel holes and cap jewels) for the balance staff, four jewels in total, better quality lever watches add a jewel as the impulse pin and two jewels for the lever pallets that lock the escape wheel, giving 7 jewels in total.
Higher quality watches also have jewels for the bearings of the lever pivots and the pivots of the train wheels. There are two jewels for the lever pivots, and two each for the third, fourth and escape wheel pivots, another eight jewels making 15 in total.
Some watches are in addition "jewelled to the centre" with two jewel bearings for the centre arbor, making 17 jewels in total. A centre jewel would be difficult to justify by any improvement it might make to timekeeping because the centre arbor turns so slowly, but it does reduce wear in the centre bearing in the plate or bridge. However, the large jewels that are needed to accommodate the centre arbor are prone to cracking. Sometimes only the top bearing is jewelled giving a count of 16 instead of 17 jewels.
A count of 18 jewels usually means 15 plus one centre jewel and two endstones for the escape wheel. A count of 21 jewels usually means 15 plus two centre jewels, two endstones on the lever pivots, and two endstones on the escape wheel pivots. This is about as much as practical and leaves only the barrel arbor without jewel bearings, which were occasionally jewelled giving a total of 23.
End stones / cap jewels
The use of endstones or cap jewels achieves two beneficial results. The first is that they form oil reservoirs, the second is that they control the end float of the arbor. Because the end float of the arbor is controlled it does not need a square shoulder and can be made "conical", a shape the prevents oil migrating along the arbor from the pivots.
In an ordinary plain jewel bearing without a cap jewel, the outer face of the jewel bearing is dished to form a reservoir for oil. When a cap jewel is added, a much better reservoir for oil is formed, capillary action causing the oil to form a globule around the pivot in the cavity between the cap jewel and the jewel bearing. When filling this reservoir it is important not to overfill it because if it touches the plate the oil will penetrate between the plate and the cap jewel setting and be dispersed by capillary attraction. There are two ways of introducing oil into this reservoir. One way is to place a drop of oil onto the cap jewel before it is put in place, which I find is difficult because the jewel can move about while you are trying to secure it, and the oil can get onto places it shouldn't. The other way is to introduce oil into the assembled setting through the jewel bearing. This is done with a fine piece of wire, or with a special oiler which makes the job easy and is my preferred method. It is sometimes said that the pivot of the balance staff will push the oil through so there is no need to lead it through by hand, but the setting should be examined after oiling to make sure that there is the right amount of oil in place. This examination is complicated if the balance assembly is in place, and if the quantity of oil is wrong, removing the balance can result in oil getting where it shouldn't
Occasionally movements are seen with cap jewels on the escape wheel pivot bearings. As the escape wheel is the second fastest turning component after the balance this would be a logical place to enhance the bearing arrangement to reduce friction. Cap jewels are usually used with conical pivots, without the square shoulder that is needed to control end float on normal parallel pivots. If the escape wheel pivots are made as fine as those of a balance staff to reduce friction, a downside of this is that they are as fragile and prone to breakage as the pivots of the balance staff itself. However, the escape wheel turns much slower than the balance, so its pivots do not need to be made so fine and can be more robust.
Sometimes end stones or cap jewels use a Kif Duofix setting, where the cap jewel is held in place by a spring that looks like the spring of a shock protection system. The spring is simply a convenient alternative to tiny screws to hold the cap jewel in place, allowing it to be easily removed and replaced during cleaning. Kif Duofix is not a shock protection system. It is often seen on the escape wheel pivots of Rolex watches.
Cap jewels are also sometimes seen on train wheel pivots.
Train arbor pivots are parallel, with a shoulder that keeps them in the right place, stopping them dropping through their bearing. However, when the watch is moved about this shoulder moves into and out of contact with the plate or jewel bearing. This causes a difference in friction, when the shoulder is in contact with the bearing the friction is higher. The oil flows along the parallel pivot surface by capillary attraction, and can get onto the shoulder of the pivot causing it to stick to the plate. A cap jewel replaces the function of the shoulder in keeping the arbor where it should be, and eliminates the problem of the shoulder of the pivot touching the plate.
These two factors, the additional oil reservoir and control of arbor end float, mean that the fact that cap jewel on train pivots are rare even in top end modern jewelled watch movements is surprising. Several companies produced endstone settings for use with train wheel pivots with square shoulders. There was "Giracap" made by Universal Escapements Ltd., the makers of Incabloc; "Fixmobil" made by Parachoc, the makers of Kif shock protection, and Lubrifix made by Seitz, the makers of Rubyshock and watch jewels.
How many jewels are actually essential?
How many jewels are necessary? Although jewels are often said to be used to reduce friction, this isn't essential and many watches were made without any jewels at all, a good strong mainspring ensuring that the watch ran. I have never seen an analysis of the effects of jewelling on the timekeeping properties of a watch, and I suspect that they are not large; timekeeping is determined by the characteristics of the balance and balance spring. A balance in a watch with a going barrel has to cope with a far greater variation in torque from the mainspring between fully wound and nearly run down 24 or so hours later than it would ever get from variations due to friction in the train.
The first bearings to be jewelled, at the beginning of the eighteenth century by Nicolas Facio (or Fatio) de Duillier, were the balance staff bearings. These are the most important bearings in a watch because the quality of timekeeping depends on the balance oscillating with as little loss of energy as possible so that the impulse that keeps it swinging can be small. Each impulse necessarily disturbs the timekeeping of the oscillating balance, so the smaller the impulse the better. This is why the balance staff pivots are made so small in diameter, and consequently are so easily broken. Balance staff jewels are usually regarded as essential in a good quality watch, although many successful cheap watches have been made without them.
Because the balance of a lever escapement is highly detached it is fairly well immune to small fluctuations in torque due to friction in the train. Jewelling of other parts of the movement is more a case of reducing wear and increasing longevity at a certain cost, rather than significantly improving the timekeeping of the watch. It might be thought that the escape pallets must surely be jewelled because of the amount of sliding friction they experience, but the Roskopf pin pallet escapement, which has no jewels at all and lasts reasonably well for a cheap watch, belies that.
In most jewelled watches, train jewels are more value in reducing friction and wear and lengthening the life of the movement than for any effect on timekeeping.
Counting jewels can be more difficult than it appears at first sight. You can't simply count the number of jewels visible on the top of the movement and double this to get the total. The reason for this is that pivots were not always jewelled in the bottom plate in mirror image to the top plate. If the centre arbor bearing in the top plate is jewelled, the bearing in the bottom plate usually isn't jewelled. Cap stones were often fitted only to bearings in the the top plate, and sometimes even only the top bearings were jewelled. This was obviously to make the movement appear jeweled to a customer, but to halve the cost of jewelling by not putting jewels in the bottom plate. This was very common practice throughout the American pocket watch industry, and also some English watches. I am not sure about Swiss practice but I am sure it would have been done by some.
When they were first used it was difficult, given the tools and equipment available, to pierce holes that were exactly central in a jewel, so jewels were first pierced to make the hole and then mounted in a metal setting that was then turned on its outside to be concentric with the jewel hole. The setting and jewel were then secured into a larger hole in the plate with small screws. These settings are called by the Swiss "chatons". At first sight this appears to be the French for kittens, but it is also name given to small gem stones, offcuts from a larger gemstone when it is being cut and shaped, like a cat producing kittens. Presumably the first watch jewels were made from these kittens or chatons, hence the name.
As technology improved it was possible to make jewels that were concentric, that is their holes and external diameters were co-axial, and chatons were no longer necessary. However, they remained in use when a manufacturer wanted to make a movement that looked impressive, but they were often only used on the visible pivots on the top plate, so were only there for show.
Once jewels were made that were concentric, the first method of setting them into the plates without chatons was called "rubbing". This was the same way that jewels were set into chatons, but now it was done directly on the plate. A feather edge was turned into the plate around the jewel hole. The jewel was dropped into the hole and then the feather edge was rubbed with a tool to fold it over the edge of the jewel, holding it in place.
When it became possible to make jewels with very accurate external dimensions, friction setting was introduced. The hole in the plate that is to receive the jewel is drilled and reamed to a very precise size and then a jewel that is a hundredth of a millimetre greater in diameter than the hole is pressed into the hole by a special press. There is enough elasticity in the materials to allow the jewel to enter the hole without shattering, and it is then held in place by friction.
A broken or chipped jewel can cut into the surface of the pivot that runs in it. A cracked jewel can draw the oil away from the bearing by capillary action. For these reasons, damaged or cracked jewels should always be replaced.
If the jewel is friction set and the correct size jewel can be located, the repair is straightforward. Likewise for a rubbed in jewel, although the procedure is less straightforward than for a friction set jewel. The major problem with replacing rubbed in jewels is finding a jewel of the correct dimensions. They are not the same shape as friction set jewels, which are cylindrical on their outer surface. Rubbed in jewels have a thinner outer edge for the setting to be rubbed over. They can sometimes be replaced with a modern friction jewel by boring out the setting but this can look out of place, and the watch is less original. Finding a jewel with the correct hole size for the pivot and outside diameter for the bored out hole in the plate can also be difficult.
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Balance assembly - balance staff in green
The picture here shows a cross section through the balance assembly of a watch. The gold coloured item is the balance, the thing you see oscillating backwards and forwards as the watch runs. The green coloured item is the shaft on which the balance turns, called the "balance staff". The red items are four "jewels" that provide hard and low friction surfaces for the staff to turn on. The two jewels that the pivots of the staff pass through are called jewel bearings or "jewel holes", and the two that the ends of the staff bear on are called "end stones" or "cap jewels". The pivots of the balance staff, the reduced diameter portions at the ends, are made very small in diameter, just a few hundredths of a millimetre, in order to minimise friction, and are hardened to minimise wear. They are therefore very delicate.
If a watch is dropped or knocked, the shock can cause the balance staff pivots to bend, or more usually to break because they are very hard and brittle, causing the watch to stop or run inaccurately. Pocket watches and early wristwatches were both subject to this problem. It was not so much of a problem for pocket watches, which were normally kept in a pocket and only received a shock if accidentally dropped, but wristwatches are in a vulnerable position at the end of the arm, where they are very prone to getting knocked.
Broken balance staff pivots were a common occurrence in early wristwatches, and every watch repairer kept a stock of spare balance staffs. Expert watch repairers could also make a new balance staff on a lathe if necessary. Turning a round shaft on a lathe is not a difficult job in principle, but the very small size of balance staff, especially of a wristwatch, which is just a few millimetres long and with pivots only a few hundredths of a millimetre in diameter, makes turning a balance staff challenging.
To overcome the problem of broken balance staff pivots, shock protection systems were devised with the idea of isolating the pivots from shocks that affect the watch. In around 1790 Abraham Louis Breguet invented what was probably the first system, which he called the "parachute" or "suspension élastique". The endstones of the balance staff were held in place by spring blades so that they move in the event of a shock, cushioning the balance staff pivots. Breguet presented the definitive version of his design at the French national industrial exhibition of 1806. Other shock protection systems followed over the years, but the first commercial and widely used shock protection system did not arrive until Incabloc was invented in the 1930s by Fritz Marti.
Today, when every modern mechanical watch has shock protection, it seems surprising that it took so long for shock protection to be adopted. The reasons for this, and the eventual universal adoption of shock protection, are an interesting story in their own right which I discuss in the section below called "slow adoption".
Fritz Marti, a Swiss engineer working at Fabrique Election of La Chaux-de-Fonds, owned by Georges Braunschweig, was well aware of the weakness of balance staff pivots and determined to do something about it. In April 1928 he created a watch fitted with a shock absorbing system that used movable balance staff jewels to protect the balance staff pivots from shocks. This design was granted Swiss patent CH 141098, filed 27 July 1929 and registered 15 July 1930. In 1931 Georges Braunschweig and Fritz Marti established Porte-Echappement Universel SA, now better known as Portescap SA, the name it adopted in 1963.
Incabloc patent CH 168494
At Porte-Echappement, Marti continued his work and on 2 March 1933 filed an application for a new patent for a simplified spring cushioned bearing system, which was granted as Swiss patent CH 168494 on 15 April 1934. Previous systems used two separate springs, one for lateral and the other for axial shocks. Marti's new design incorporated a cone shape for the bearing housing that redirected lateral shock in an axial direction, thus requiring only one spring. Production started in June 1933 and the Incabloc trademark was registered by the company in Switzerland on 6 July 1933.
All shock protection systems work in basically the same way. The balance staff jewel bearings are held in place by light springs instead of being mounted rigidly in the plates. When a shock occurs the springs allow the jewels and pivots to move slightly, and a stronger part of the balance staff contacts a fixed part of the housing to take the shock. Once the shock is absorbed, the springs return the jewels and pivots to their correct positions.
The figure from the patent reproduced here shows this in action. In Fig 3 the balance staff has received a lateral impulse shown by arrow A. The staff pivot and its jewel bearing have mode to the right in the housing, and the cone shape of the jewel setting has caused it to ride up in the housing, lifting the cap jewel 5 against the spring 6. The stronger part of the balance staff 9 has contacted the housing to absorb the shock. In Fig 4 the balance staff has received an axial impulse shown by arrow B. In this case the jewel bearing and cap jewel have both been lifted vertically against the spring and the shoulder of the balance staff 10 has contacted the housing to absorb the shock.
Two of the first companies to adopt Incabloc were The West End Watch Co. in 1934 for their Sowar Prima, which became West End's most successful model, and Mido in 1935 for the Mido Multifort, became the best selling Mido watch until the 1950s. Both companies were also early adopters of the Taubert / Borgel company's waterproof decagonal case.
Incabloc advert September 1935
Incabloc provided a real and commercial solution to the problem of broken balance staff pivots, but it wasn't immediately widely adopted. In fact, Incabloc was only one of many shock protection systems that had been developed since Breguet invented his "parachute" in 1790, but for some reason watch manufacturers were reluctant to incorporate these into their designs. The reasons for this, and the eventual universal adoption of shock protection, are an interesting story in their own right.
Shock protection for the balance staff pivots added extra cost, and most manufacturers were very cost sensitive, knowing that a higher price point would cost sales. There was also no demand at the time from the public for shock protection; everyone knew that watches were delicate and that if you dropped them they were liable to break, every watch repairer at the time was very well used to replacing balance staffs, and spare balance staffs were readily available from the manufacturers.
It might be thought that the military would be the first to require that shock protection be fitted. A watch with broken balance staff pivots is useless, and if that happened in the middle of a military manoeuvre it could be dashed inconvenient. One would think that army types would be breaking balance staffs left right and centre, but in fact the military were among the most reluctant to see watches fitted with shock protection.
The British "Army Trade Pattern" A.T.P and "General Services Trade Pattern" G.S.T.P. specifications emerged after the Great War and governed all British Army watches used before and during World War II, until they were superseded by the "Watch, Wrist, Waterproof" or "W.W.W" specification in 1945 at the end of the war. Neither the A.T.P, G.S.T.P. or the original 1945 version of the W.W.W. specification required shock protection, even though by the time of the W.W.W. specification shock protection of various forms had been commercially available for many years.
It is clear from this that breakage of balance staffs was not a great inconvenience to the British military. In fact, there was a dispute in the military committee that drew up the W.W.W specification about whether the benefit in reduction broken balance staffs result from shock protection would be offset by the increased time required for regular service of watches with shock proof settings, estimated at 10 - 15 minutes per watch. This was a red herring because it is actually quicker and easier to service a shock resistant setting where the jewels are held in place by clips, than an old style setting with end stones held in place by screws. Nevertheless, it was not until 1947 that an amendment to the W.W.W. specification introduced a requirement for shock protection.
The conclusion must be that that the general public and the military types who actually needed a wristwatch to perform their duties (mainly officers, not squaddies who were jumping in and out of trenches etc.) took care of them and that broken balance staffs were relatively rare. Before the second world war, vigorous pursuits such as trekking, diving and mountain climbing were the realm of a few and not followed as widely as they are today. If people outside the watchmaking profession even realised that shock protection was possible, they probably didn't think that they needed it.
The power of advertising
Shock protection was initially more widely advertised in America than in Europe. It seems that in America, with its more developed advertising industry, shock protection was used as an extra selling point or feature that could be used in advertising, persuading consumers that they needed it and to pay the extra that a watch with the feature cost. Once watches that were "shock proof" entered the public's consciousness, the early adopters of such watches acquired "bragging rights", and any watch that didn't have shock protection was deemed old fashioned.
The feature that made Incabloc a commercial success, and the system that within a short period dominated the market for shock proof settings, was that it was very cleverly designed. It was easy for manufacturers to add to their movements, and it also speeded up watch servicing.
All balance staffs had, and still have, the same four jewels; two bearing or "jewel holes", and two "end stones" or "cap jewels". These all need to be cleaned when the watch is serviced, which means removing the cap jewels. In a watch without shock protection the cap jewels are held in place by one or two small screws. Fritz Marti's clever idea was to hold the cap jewel in place with the, now instantly recognisable, shaped Incabloc spring clip, which was also the spring that allowed the jewel to move when a shock occurred. Instead of taking longer to service than a setting without shock protection, Incabloc was faster, because instead of fiddling about with tiny screws, simply releasing the Incabloc spring, which was cleverly also held captive to the setting, allows the cap jewel to be removed, and then quickly clipped back into place after cleaning and oiling. This additional benefit was soon recognised and Incabloc came to dominate the market for shock proof settings.
The lifetime of Swiss patents in the 1920s and 1930s was normally 15 years, so Marti's patent for the original Incabloc system would have expired in 1949. After that many other shock protection systems such as Kif followed.
Shock protection is a real benefit, and today owners don't have to treat their watches as if they are delicate. A modern mechanical watch can be bashed about with gusto, and some owners take pride in wearing a watch that shows scars from trekking, mountaineering or diving. The only downside is for collectors of watches that were made before shock protection was widely used. The days of the local watch repairer who could replace a balance staff are now long gone, and watch repairers who can do this are few and far between, which makes replacing a staff with broken pivots an expensive operation. So if you have a watch without shock protection, take care of it!
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The first watches were wound and set by a separate loose key. A common arrangement was for the mainspring to be wound from the back and the hands set from the front. The spring is wound by passing the key through a hole in the inner case back and onto the square end of the fusee arbor, or the barrel arbor in going barrel watches. Turning the key winds the spring. To set the hands the front bezel is opened and the key is applied to a square on the boss of the minute hand. Turning the key moves both the minute and hour hands.
Using a key to wind and set a watch has numerous disadvantages: the key can get lost, the hole in the case back lets in dust, and the dial or hands can easily be damaged. To overcome these problems mechanisms were invented that allowed the watch to be wound and set using a button or crown on the end of the pendant, the tube that projects from the side of the case and carries the bow. This meant that a separate loose key was not needed and, in the nineteenth century, such watches were called "keyless". Today almost all watches are keyless and it is only antique watches that are key wound so the term keyless has fallen out of use.
The mechanism that allows you to wind the watch mainspring and set the hands by turning the crown or button is called the "keyless work". The keyless work shifts gears into and out of mesh so that the different functions of winding and setting can be performed by turning the one crown. There are different ways of changing the keyless work from winding to setting; these are described in separate sections below.
There many designs and patents for different keyless mechanisms. Thomas Prest, an apprentice, journeyman and then foreman to John Arnold the chronometer maker, was one of the first to design a movement with keyless winding, applying for a patent that was granted No. 4501 date 20 October 1820 for "A new and additional movement applied to a watch, to enable it to be wound up by the pendant knob without any detached key or winder". Prest's design was only applied to movements with a going barrel so it found little favour with English watchmakers who continued to prefer fusee movements.
In Switzerland Louis Audemars invented a form of keyless winding in 1838. In Britain Adolphe Nicole devised keyless mechanisms for both going barrel and fusee movements, for which he was granted British patent No 10,348 in 1844. Nicole initially worked in Switzerland as a partner in the company Nicole & Capt, setting up a London branch in 1840. When Jules Capt died in 1876 Nicole took on the Dane Sophus Emil Nielsen as partner and the company became Nicole, Nielsen & Co. This company produced many of the finest London watches nineteenth century.
Sliding sleeve keyless work: mouse over to operate
In 1845 Adrien Philippe, who later joined the company of Count Patek and which subsequently became Patek Philippe, invented the modern form of "sliding sleeve" or "shifting sleeve" keyless works. Philippe filed a patent application on June 5, 1845 and was awarded French Patent No. 1317 for "Mechanical system or device for winding and handsetting of watches via the pendant". This mechanism is found in almost all keyless watches from the late nineteenth century onwards.
Two pinions sit on the stem, the winding pinion and the sliding pinion. On the mating faces of the two pinions are inclined teeth that form a Bréguet ratchet - it is this the teeth of this ratchet slipping over each other that you feel when you are winding a watch and turn the crown backwards. The sliding pinion sits on a square section of the stem and is normally held in contact with the winding pinion so that turning the crown winds the watch. To set the hands the sliding pinion is made to slide along the square section of the stem, either by pulling out the crown or by pressing the pin set push piece, so that it disengages from the winding pinion and teeth on its other end engage with the setting wheels.
The image shows a stem set sliding sleeve mechanism from a Marvin watch movement. If you mouse over it you should see the action of pulling out the stem to set the hands.
In the usual position the setting lever engages with a groove on the stem just above the winding pinion. When the crown is turned the sliding pinion turns, driven by a square section of the stem below the winding pinion. The sliding pinion then turns the winding pinion through the Bréguet ratchet that couples the two pinions.
When the stem is pulled out the setting lever presses down the yoke, which makes the winding pinion slide down the square section of the stem. The disengages the winding mechanism and engages the hand setting mechanism, the small train of wheels that connect to the motion work.
However, despite the efforts of numerous inventors over centuries the keyless work remains the worst designed part of a watch from the point of view of lubrication and longevity, and many watches have been scrapped over the years because of wear in the winding mechanism. From this point of view an automatic self winding watch is a benefit in a watch for everyday use.
Rocking Bar and Sliding Sleeve
There are two basic types of mechanism that are used to change keyless work from winding to setting mode; rocking bar and sliding or shifting sleeve. The rocking bar mechanism uses a bar with gear wheels mounted on both ends. The bar is rocked to engage one or the other wheels to change the mechanism from the winding to hand setting mode. The sliding sleeve mechanism uses gears that slide on the winding stem to change the mechanism from winding to hand setting mode. Both rocking bar and sliding sleeve mechanisms can be operated by the crown moving the stem, called crown or stem set, or by a push piece on the side of the case, called pin set, or by a lever.
The rocking bar mechanism is conceptually simpler, and is the older of the two. The sliding sleeve mechanism was invented in 1845 by Adrien Philippe.
Pin or nail set, and lever set
Pin or Nail Set
Pin, or nail, set and lever set are alternatives to stem setting for putting the keyless work into the hand setting mode. In both the pin set and lever set mechanisms the crown remains in its normal position against the case during both winding and hand setting. Pin set and lever set are seen on nineteenth century pocket watches, and also on early wristwatches.
The pin or lever set mechanism is more robust than the stem set mechanism, which is actuated by a small projection from the setting lever that engages with a groove on the stem. Because these parts are so small and not well lubricated they often wear and cause problems, such as the stem pulling out completely when the wearer tries to set the watch. The pin set and lever set mechanisms don't suffer from this problem. By the 1920s pin and lever set were seen increasingly as old fashioned and were phased out in favour of stem set.
- Pin set is a mechanism which uses a pin on the side of the case close to the crown to engage the hand setting mode. The pin is indicated by the red arrow in the picture. With the pin in its normal position, turning the crown winds the main spring. When the pin is pressed in, turning the crown sets the hands. When the pin is released it springs back to the winding position. This type of keyless work is sometimes called "nail set", because a finger nail is usually used to depress the pin.
- Lever set is an alternative form of setting that is similar in concept to pin set. Instead of pressing in a pin, a lever is pulled out to engage hand setting. This lever is often covered by the watch bezel, so the front cover of the watch must be opened to operate it. Lever set was required by American railroad companies to make it almost impossible to set the hands accidentally, after a serious railroad accident was thought to have been caused by this happening.
Positive and Negative (American) stem setting
If a watch is set to the correct time by pulling out and then turning the crown it is called "stem set". This is because the outward movement of the stem when the crown is pulled out puts the keyless work into the hand setting mode. There are two classes of stem set keyless works, positive and negative set. In both forms the normal position of the crown against the case is the winding position and the crown and stem are pulled out from the case to put the mechanism in the hand set mode. The difference is in which way the mechanisms are biased by their internal springs.
Positive set keyless work
Positive set keyless work is the most common form in Europe. Because it is so common, "positive set" is usually omitted and it is just called stem setting. In this type of keyless work a long stem extends from the crown into the movement and is held in place in the movement by a projection on the setting lever that engages with a groove on the stem. The setting lever is held in place by a small screw that is trapped between the plates. The head of this screw is visible on the top plate or bridge near to the axis of the stem. To release the stem the setting lever screw is slackened a couple of turns which moves the projection on the lever aside and the stem can then be pulled out from the movement and case.
When the movement is in the case, the setting lever screw is tight and the crown is pushed to the side of the case, the keyless work is put into the winding mode. When the crown is pulled away from the watch case to set the time, the setting lever moves and puts the keyless work into the hand set mode. The pull on the stem is a direct, positive, action on the keyless work, hence the name. A detent in the keyless work holds the mechanism in the hand set position until the crown is pushed back to its normal position against the case.
Negative set or American keyless work
Negative set detent spring sleeve
Negative set or American keyless work was widely used in American made watches because the watch movement and case were often combined only at the point of sale, so that a customer could choose which movement he wanted and which case he wanted, and the sales assistant would then put the movement into the case. This needed to be easily done without requiring a workshop or tools and negative set keyless work was used. With negative set keyless work there is no setting lever screw.
Negative set keyless work is spring biased into the hand set mode; this is the mode the keyless work adopts when the movement is out of the case. To put the movement into the case the crown is pulled out and the movement inserted into the case. When the crown is then pushed in it puts the keyless work into the winding mode, which is where it remains unless the crown is pulled out to set the hands or remove the movement from the case.
The image here shows a cross section through the pendant of a watch with negative set keyless work. A short "case" stem or "American stem" is fitted in the pendant or stem tube of the watch case. This stem is not attached to the movement but the square section on the end of the case stem engages with a square socket on the end of a short stem in the movement. Once the movement is put into the case the case stem is used to push the keyless work into the winding position, against the spring in the keyless work. A detent in the pendant holds the crown stem in this position whilst the watch is in use.
The detent that holds the case stem in one of two positions is formed by grooves in the stem and a split spring steel sleeve that I have coloured grey in the image. The sleeve is split at its lower end to form four claws that grip the stem. The spring sleeve is held in place by an externally threaded brass plug that is coloured yellow. In the image the case stem is in the normal winding position although the movement is not shown. When the crown is pulled out the claws of the sleeve are forced open by a taper to allow the swelling on the stem to pass, and then they grip the groove in the stem below the swelling and hold the crown in the hand setting position.
When the crown stem is pulled out into the hand setting position, the spring in the keyless work pushes it into the hand set position - so the stem doesn't "pull" the keyless work into the hand set position. The keyless work assumes the hand set mode when it is not held in place by the crown stem, so the action of putting the keyless work into the hand set mode is by removing something which is stopping it, a negative rather than positive action, hence the name negative set.
Watches by Cyma sometimes have movements with the American negative set keyless work and are engraved "US Pat 24 May 1904", reference to patent US 760647 for a negative set stem winding and setting mechanism (keyless work) granted to Sandoz on that date, a US version of a Swiss patent granted to Sandoz in 1903. You can see details of a movement with this feature on my Movement Identification page.
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In the wristwatches I am interested in, centre seconds, that is where the seconds hand is pivoted in the centre of the dial at the same point as the hour and minute hands, are rare. The reason for this is that it is not easy to get a movement that is laid out in the traditional nineteenth century way, as shown above, to drive a centre seconds hand.
When a centre second hand is fitted to a movement with traditional layout, it is done by extending the arbor of the third wheel through the central bridge and mounting on the end of this extended arbor a wheel which drives a pinion on the centre seconds arbor. If you look at the picture here you can see the wheel on the third wheel pivot clearly. The pinion on the centre seconds arbor is almost completely covered by the end plate of a spring. The purpose of the spring is to hold the centre seconds arbor in place, whilst at the same time creating some friction to dampen down fluttering of the seconds hand.
Because the seconds hand pinion is not part of the train of wheels carrying power from the mainspring to the escapement, but is driven indirectly by the wheel on the third wheel pivot, this arrangement is called "indirect centre seconds". The speed of the seconds hand has to be geared up from the slower-moving third wheel, and because the centre seconds arbor is not driving anything there is nothing to stop it fluttering backwards and forwards a small amount each time it gets a kick from the third wheel, due to the play or backlash in the gear teeth.
Direct Centre Seconds
Fluttering of the seconds hand can be eliminated by rearranging the layout of the gear train to place the fourth wheel at the centre of the movement. The fourth wheel rotates once a minute and therefore in this layout it can drive the centre seconds hand "directly", by mounting the seconds hand on an extension of the fourth wheel arbor. This was very common in English watches but was rare (did not exist?) in Swiss watches before the twentieth century.
The cannon pinion that carries the minute hand, and drives the hour hand via the motion work, is still driven off the arbor of the second wheel, that is the wheel that was called the centre wheel until it was moved off-centre to make way for the fourth wheel. In this arrangement, the arbor of the second wheel is extended through the bottom plate and carries an intermediate wheel that drives the cannon pinion and the motion work.
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The motion work is a set of wheels under the dial that takes the motion of the centre wheel, which turns once an hour, and divides it by twelve to drive the hour hand.
Motion work with indirect centre seconds
The picture here shows how the motion works operates. The drive from the great wheel turns the centre wheel, coloured yellow. The rate at which this turns is of course governed by how quickly the escapement, through the "going train", allows it to turn, which is arranged to be once an hour. The arbor of the centre wheel is extended through the bottom plate and the dial and turns the cannon pinion, which carries the minute hand on a pipe extending from the pinion.
The pipe that carries the minute hand is what gives the cannon pinion its name. In watchwork a pinion is a small gear, such as the one at the base of the cannon pinion. Etymologically the word cannon means a 'large tube', derived from the Latin canna for reed, which also gives us the word 'cane' for tall grasses with hollow stems, especially bamboo or sugar cane. So the cannon pinion is simply a pinion with a large tube attached to it.
To drive the hour hand, the cannon pinion turns the minute wheel, which carries a smaller pinion that drives the hour wheel. Why this is called the minute wheel escapes me, because it neither carries the minute hand nor turns once a minute. But it has to be called something, and minute wheel it is.
The gearing of the cannon pinion to the minute wheel and the minute pinion to the hour wheel are arranged to give an overall 12:1 step down in turning speed, so that the hour wheel turns once in twelve hours. The hour hand is mounted on a pipe projecting from the hour wheel. Using the same logic as for the cannon pinion, this could have been called the cannon wheel, but it isn't.
The cannon pinion is a friction fit on the centre arbor so that the hands can be turned to set the time. The cannon pinion has a slight indent that snaps into a groove on the centre arbor as shown in the picture. This stops the cannon pinion from floating up and down on the centre arbor, and also provides the means by which the friction between the cannon pinion and the arbor is controlled. If the friction is too great, the hands cannot be set easily, but if it is too small the hands slip whilst the watch is working and don't indicate the correct time. The friction between the cannon pinion and the centre arbor is increased by lightly tapping the indent with a punch to make it grip tighter, or decreased by broaching the hole in the cannon pinion. To prevent the hour wheel from floating up and either rubbing on the dial or causing the hour hand to touch the crystal, a very thin concave brass dial washer is usually fitted as shown in the picture.
If a centre seconds hand is fitted, as is shown in the picture, this is driven separately and not connected to the motion work. It is driven either "indirectly" from the third wheel as shown in the picture, or "directly" by rearranging the layout of the movement to bring the arbor of the fourth wheel to the centre as described in the section about Centre Seconds elsewhere on this page.
If there is no centre seconds hand the centre wheel arbor is solid in modern movements. In older movements, mainly pocket watches and some very early wristwatches, a Lépine friction centre post was used to drive the cannon pinion. This replaced the extended arbor of the centre wheel with a post or pin fitted into a hole bored through the shortened arbor of the centre wheel. This pin is a friction fit into the hole in the centre wheel and drives the cannon pinion. Its purpose is to allow the hands to be set by a key from the back of the watch.
The friction centre post was invented by Jean Antoine Lépine in the eighteenth century. Before this invention the hands were set by applying a key directly to a square boss on top or front of the cannon pinion, which meant that the front of the case, the bezel carrying the crystal, had to be arranged to open, and also that there was the constant danger of the owner slipping with the key and marking the dial or damaging the hands. Lépine's invention allowed the bezel and crystal to be fixed to the middle part of the case, which made the case simpler, and allowed the crystal to have a lower dome, which made the case slimmer. This was just one of Lépine's contributions to the design of the modern watch.
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The cylinder escapement (also called the horizontal escapement to differentiate it from the verge escapement that preceded it) is usually looked upon rather sniffily by collectors, and although it was invented in England by Thomas Tompion in 1695 and improved by George Graham, an apprentice of Tompion, it was never really embraced by English watchmakers.
Cylinder escapement from Saunier
The image here is based on an image in Saunier's "Treatise on Modern Horology". Fig. 1 on the left shows why the cylinder escapement is so called, a cylinder with its wall partly cut away forms the arbor on which the balance turns, the two plugs at the top and bottom carry the balance pivots. The cut away part of the cylinder wall at the top allow the oddly shaped teeth of the escape wheel to pass as the balance swings. The wider cut away at the bottom allows the tooth support to pass.
The plan view Fig. 2 shows how the escapement works. The figure shows a series of actions by showing the cylinder in white adjacent to successive teeth of the escape wheel; in reality of course the cylinder turns back and forth in one place while the escape wheel ticks round. I have labelled the different steps in red.
At step 1 the lip of the cut out is receiving impulse from the inclined face of an escape wheel tooth as it enters the cylinder. Step 2 shows the tooth locked against the inside of the cylinder. Steps 3 and 4 show how the tooth remains locked as the balance swings to its full amplitude and then swings back. In step 5 the tooth is about to escape from the other side of the cylinder. Step 6 shows how the inclined face of the escaping tooth gives impulse to the cut out in the cylinder. Step 7 shows the tooth dropping onto the outside of the cylinder; this tooth is of course actually the next tooth around on the escape wheel.
Because a tooth is always in contact with the cylinder this is called a "frictional rest" escapement. It is often said that a cylinder escapement cannot keep good time, but Saunier explains that once optimum proportions and materials had been arrived at after some years of development in Switzerland, a watch with a cylinder escapement and without a fusee was a far better timekeeper than a watch with a verge movement with a fusee.
In "Watchmaking in England, 1760-1820" by Leonard Weiss I found the following in a quote from 'A Mechanic' in 1859 which throws an interesting light on the situation:
"The horizontal escapement was invented in England, and was found by its frictional action during the state of rest of the train so nearly to counter-balance the variable impulse given by the spring, that even with the crude going—barrels the average performance of the watch was amazingly improved. English engineers had by experiment proved that friction was much less between different metals than between similar, therefore the watchmaker made the horizontal wheel of brass and his cylinder of steel. Meanwhile public taste demanded flat watches, and the Swiss made the horizontal escapement of steel entirely, thereby sacrificing theory to demand. After a time it was found that, whereas the brass wheel destroyed the cylinder very quickly, the steel wheel hardly marked it in years of wear, clearly showing that even if there be a slight excess of that friction that retards motion, it is a less evil than the absolute wear of the machine itself. The Swiss were thus rewarded for studying the taste of the public by a large trade, and have made their country the home of the horizontal escapement."
The point that 'A Mechanic' is making is that because the cylinder escapement is a "frictional rest" escapement it should, in theory, be improved by minimising friction and therefore using a combination of brass and steel for the wheel and cylinder. However, the friction of the cylinder is actually beneficial to timekeeping, because it evened out the torque from the mainspring in a movement with a going barrel, i.e. without a fusee.
The feature of the cylinder escapement that caused so much objection to English watchmakers is that the escape wheel is always held in contact with some part or other of the cylinder. The force of the main spring presses the escape wheel against the cylinder causing friction. But this objectionable friction is also the secret of the unexpectedly good timekeeping of the cylinder escapement. When the main spring is fully or near fully wound and the force it exerts is at it highest, the friction in the escapement is also at its highest. As the main spring runs down it produces less force and the friction in the escapement decreases.
The combination of high torque with high friction and low torque with low friction results in a greater consistency of amplitude of the balance between fully wound and nearly run down. If the balance and spring were perfectly isochronous this wouldn't matter because the period in big and small amplitudes would be the same, but perfection is difficult to achieve, especially with eighteenth and nineteenth spring technology, and the greater consistency of amplitudes resulted in a rate that was more constant than might have been expected. The combination of steel on steel used by the Swiss produced a superior timekeeping performance to the lower friction combination of brass on steel favoured by the English watchmakers for theoretical reasons.
The other problem with the brass wheel and steel cylinder combination used by the English watchmakers was that the softer brass picked up particles of dust which embedded themselves into the surface of the escape wheel, turning it into a grinding wheel as it rubbed against the steel cylinder, thus wearing it away very quickly. The Swiss combination of steel wheel and steel cylinder didn't suffer nearly so much from this problem, although dust in the oil will still cause wear over the years.
English watchmakers couldn't get over their view that using steel on steel was bad engineering, so when they did make cylinder escapements they used brass escape wheels and then, observing that these wore out quickly, condemned the cylinder escapement. The Swiss however were not so purist and observing that steel on steel worked very well, even if it shouldn't in theory, made millions of watches with cylinder escapements, which they sold cheaply to happy customers, who didn't know or care about the difference between a cylinder and a lever escapement and were just happy to get a cheap watch that told the time reasonably well. And we all know what happened to the Swiss and the English watch making industries as a result of this difference in attitudes.
Identification and care of a cylinder escapement
How can you tell if a watch has a cylinder rather than a lever escapement? The picture here is of a movement with cylinder escapement. If you start at the centre pivot, the one right in the middle of the picture, you can then identify the pivots of the third and fourth arbors. The next wheel in the train is the escape wheel, and in this movement the pivot for the escape wheel arbor is underneath the balance — the red arrow is not pointing to the balance. This is because the teeth on the escape wheel engage directly with the cylinder, which is part of the balance staff. There is no lever between the escape wheel and the balance staff as there is in a lever escapement, so the escape wheel of a cylinder escapement has to be planted right next to the balance staff.
The DF&Co mark stamped onto the movement show that it was imported into Britain by Dimier Brothers who were large and important watch importers in the nineteenth century. The ébauche is nicely finished with "frosted" (matted and gilded) plates and jweled pivots for the train wheels, a typical basic product of the "Swiss watch industry" in the nineteenth century. At the time British retailers did not allow basic items like this to carry brand names so most watches from the period are anonymous products of "the Swiss watch industry".
Although the performance and longevity of Swiss made cylinder escapements with steel escape wheels and steel cylinders was better than English ones with brass escape wheels and steel cylinders, the difference is relative rather than absolute; the cylinder wears more slowly with the Swiss steel escape wheel, but it still does wear as the oil picks up dust and turns to a fine grinding paste. They were also usually at the lower end of the price scale so the train pivots are not jewelled. Jewels in watch movements are not just there to look pretty, or even to reduce friction; their principal role is to provide a hard bearing surface the reduces wear. An watch without train jewels needs servicing more than one with jewels if wear of the bearings in the plates is going to be kept within acceptable limits.
The only way to delay the inevitable is to have the movement regularly serviced, when it will be cleaned to remove the old mixture of oil and dust and lubricated with fresh clean oil. This should be done before the performance starts to deteriorate noticeably, because by then the damage can have been done, and replacing a cylinder is a job that fewer and fewer watch repairers are prepared to do. Even if you can find someone who will take on the task, it may be uneconomic because, in the main, watches with cylinder movements are not very collectible and therefore not highly valued.
The great Abraham Louis Breguet overcame the problem of wear in the cylinder escapement to a very great extent by making his cylinders of ruby, but don't expect to find such an exotic device in a cheap Swiss watch.
If you contrast this picture with that of the lever escapement at the head of this page, concentrating on the escape wheel and the cock that holds its upper pivot, you will soon be able to see the difference.
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Stop work and recoil clicks
A mechanical watch is driven by the power stored in a spring. This is called the "mainspring" to distinguish it from other springs in the movement such as the balance spring. In almost all modern watches the mainspring is contained in a barrel that has teeth on its outside. The inner end of the mainspring is 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 makes the barrel turn, which drives the train and the escapement, making the watch run.
The arbor can turn inside the barrel, and when you wind the watch this is what happens. The arbor winds the spring around itself, increasing the power in the spring and the turning force on the barrel. A ratchet stops the arbor turning backwards. When the mainspring is fully wound, any further turning force cannot go into winding the spring further and instead goes directly into driving the train. If you apply further pressure to the winding mechanism, this is transmitted directly to the wheel train and hence 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.
Optimum mainspring operating range
The torque (turning or twisting force) exerted by a watch 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. 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 and the torque can be much higher or lower as shown in the diagram here.
The optimum operating range for the spring is the portion shown between the red lines which is near "Hooke's law" linear, avoiding the extremes of high and low torque at either end of the range. In this region the balance and balance spring can be designed to function near isochronously; that is with the same frequency despite the variation in driving torque which causes a change in the amplitude of the balance as the spring runs down. This is discussed further under Isochronism.
If the spring is wound fully and tightly around its arbor, the very high torque that this creates, shown by the grey shaded region of the graph, can cause "over banking" in a lever escapement — the balance is impulsed so much that it turns further than it should and the impulse pin strikes the outside of the lever fork. This not only results in inaccurate timekeeping but can also damage the escapement. To prevent this various forms of "stop work" are used to stop the mainspring being wound tightly around its arbor.
As the spring unwinds the torque it produces reduces as shown in the figure, and the amplitude of the balance will be reduced. The effect of this on timekeeping is minimised by making the balance and balance spring assembly as near to "isochronous" as possible. A fully isochronous balance/spring assembly will oscillate with the same period or frequency irrespective of the amplitude, and it is possible to design the balance spring assembly to be near isochronous in the region shown as the optimum operating range of spring torque.
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, that its purpose is 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 Myths about stop work
Maltese cross or Geneva 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 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.
When the watch is being wound and the stop work prevents the arbor turning any further, the force of further winding is reacted against the mainspring barrel by the Maltese cross. If the owner applies further pressure to the winding mechanism, this is transmitted through the barrel directly to the wheel train and hence the escapement, producing the very effects of excessive amplitude and potential over banking that the stop work was designed to avoid. This also happens if there is a recoil click, or no form of stop work at all. 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.
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 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.
It was eventually realised that the extra cost of and complexity of stop work was not justified. It was advances in spring technology that brought this about, modern springs are much longer than those used in the early days of watchmaking. A modern spring needs only to be backed off a small amount to avoid the undesired high torque when it is fully wound. Today manually wound watches usually have a simple "recoil click" instead of stop work.
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.
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.
Myths about stop work
There is a common misunderstanding about stop work, that its purpose is prevent the spring from unwinding beyond a point where it becomes weak and causes the watch to loose accuracy. This is not correct.
As I explain above, the purpose of stop work is to prevent the barrel being further wound at the end of winding 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 and stop the watch before the spring is fully unwound. However, this is a consequence of the design rather than its primary purpose, and rather than preventing a loss of accuracy, stopping a watch results in a total loss of accuracy and is an inconvenience 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, and it can be wound and corrected to time when the opportunity presents itself. However, a watch that has stopped has totally lost accuracy. Even if it was within one second of the correct time before it was stopped, as each second passes it becomes one second less accurate. (Until 12 hours have elapsed, when it is right again - although of course the owner cannot know this from simply looking at the watch.)
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 find a clock or sundial to set the time correctly against, which in earlier times might not be so easy.
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."
As George Daniels says, manually wound watches without stopwork have a recoiling pawl that allows the barrel to turn backwards slightly, to "recoil", and let the mainspring uncoil a little from being fully wound. All modern manually wound watches have recoil clicks. Automatic watches allow the mainspring to slip in the barrel at the end of winding so that the watch is not wound too much, either manually or automatically.
A recoil click of course does not stop the spring running down. To avoid the very low torque when the spring is near fully unwound, 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 will not be encountered in normal use.
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Early spring driven timepieces didn't have balance springs. This meant that their balance had no inherent natural frequency, it was simply slicked back and forth by the escapement. The time that each movement took depended on how hard the escapement pushed on the balance, so the rate varied greatly if the driving force changed.
To keep the rate of such a timepiece constant a fusee was introduced between the mainspring and the train. A fusee is shaped like a cone and connected to the mainspring barrel by a chain. When the mainspring is fully wound and its tension at its greatest, the chain pulls on the smallest diameter part of the fusee cone. As the mainspring runs down and its force diminishes, the part of the fusee cone that the chain pulls on increases proportionally in diameter. This keeps the force applied to the train, and hence to the balance by the escapement, constant.
When the balance spring was introduced, the combination of balance and spring had a natural frequency that resisted changes in its rate due to variations in the force exerted by the train. Improved designs of escapement reduced the influence of the force of the mainspring further, culminating in the 1820s in England with the highly detached English lever escapement. A fully detached balance and spring would be isochronous, i.e. would oscillate with the same frequency irrespective of amplitude, but no practical watch balance can achieve this because it needs to be impulsed to keep going. However, improved designs increasingly approached the ideal. Arnold and Breguet recognised that the shape of the outer coil of the balance spring could be altered to reduce the "point of attachment" error and improve iscochronism. With these developments, the detached lever escapement and overcoil balance spring, the improvement in timekeeping of an ordinary watch from employing a fusee was negligible. However, English watchmakers throughout the nineteenth century persisted with the fusee — but why?
Marine chronometer compensation balance
There was one branch of English horology where the fusee was not an unnecessary complication but a vital necessity. Marine box chronometers could not achieve the required level of precision in their timekeeping without it. But these machines had very highly detached spring detent escapements, and balance springs with exquisitely formed terminal coils, so were their balances not isochronous? No. Because as part of their means of compensating for variations in temperature the rims of the balances were cut through in two places, which made them sensitive to centrifugal forces.
The dotted lines on the figure here shows how a cut bimetallic balance compensates for changes in temperature. When the temperature rises the balance spring gets weaker, so the bimetallic arms curl inwards to reduce the moment of inertia of the balance. The opposite happens if the temperature rises. The problem is that cutting the rim to make arms that can move like this also allows them to move under centrifugal force.
While the movement is working, the balance is stationery at two places during every oscillation at either end of its swing. When the balance stops the balance spring accelerates in back towards the central point where it unlocks a pallet and receives impulse. As this occurs the balance is travelling with maximum speed, and this speed causes a centrifugal force to act on the rims and their masses, causing them to flex outwards. This increases the moment of inertia of the balance which affects the period. If the amplitude is always exactly the same, then this does not matter because the effect will be exactly the same on every cycle. But if the amplitude varies, then the speed of the balance as it passes through the central point will vary, so the effect will be different and affect the period.
In 1887 Victor Kullberg, of the eponymous and famous chronometer making company, asked the Astronomer Royal to rate a chronometer as it was fitted with four different balances. The chronometer was an ordinary large two day type and it was deposited at the Observatory on 18 April. With it were four balances of practically the same diameters but different constructions.
- A plain brass balance, not cut, with four quarter timing screws. Thickness of rim: 0.085 inch.
- An ordinary compensation balance, two timing screws and two compensation masses. Thickness of rim, 0.038 inch ; length of acting laminae 135° ; distance of centre of compensation masses 98° from bar.
- A steel balance with brass inlaid, two timing screws, two compensation masses. Thickness of rim, 0.035 inch ; length of acting laminae 141° ; half the laminae on each side compensated next to bar ; distance of centre of compensation masses 100° from bar.
- Same as No. 3 but with laminae 0.024 inch thick ; acting length of laminae 150° ; two small screws at ends of acting laminae, each weighing three grains ; distance of centre of compensation masses 61° from bar.
The balances in large arcs made one turn and a fifth, and in short arcs three-quarters of a turn. The last three balances were accurately adjusted for temperature, and as the variations of temperature were so small, it can be assumed that the rates are unaffected by temperature. When balance No. 1 was fitted, the chronometer was placed in the oven at an even temperature. Below are the mean daily rates :-
|Long arcs||Short arcs||Difference|
Winding a fusee or going barrel
If you are looking at the back of a English fusee key wound watch, which you will usually be when winding it, then the minute hand (if you could see it) would appear to be going anticlockwise and therefore when viewed from the back the great wheel must turn clockwise. The great wheel is driven by the fusee cone through a ratchet, and during normal running the fusee must also be driven to turn clockwise to drive the great wheel, so this is the direction the mainspring barrel must pull the fusee through the fusee chain. As the watch runs down, the chain is drawn off the fusee and onto the mainspring barrel, so when you wind the watch you need to reverse this and draw the fusee chain off the barrel and onto the fusee cone, in the process winding the mainspring, and so you have to turn the fusee anticlockwise. It doesn't matter whether the spring barrel in a fusee watch turns clockwise or anticlockwise, in the "reverse fusee" the mainspring barrel turns in the opposite direction to the barrel in a standard fusee.
In a watch with a going barrel, the barrel, which has the great wheel teeth cut on its outside, when viewed from the rear of the watch, must always turn clockwise. With a key wound going barrel, you turn the barrel arbor clockwise to wind the spring in towards the centre of the barrel, and the spring uncoils outwards as the barrel also turns clockwise driving the train.
Sometimes watches with going barrels had an extra gear incorporated so that the barrel was wound anticlockwise. This was to simulate the anticlockwise winding of a fusee watch.
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English and American watch sizes
The photograph here shows the dial plate of an English lever watch. The initials JW are for John Wycherley of Prescot, an English pioneer of mass produced rough movements or "frames". In 1866 Wycherley set up a factory in Warrington Road, Prescot, with three floors and steam power to produce by machinery plates and other parts that were interchangeable.
Above Wycherley's initials are a set of numbers that define the essential dimensions of the movement, often called in English watchmaking the "calliper" of the movement, derived from the measurement of the diameter of the bottom (dial) plate measured by a pair of callipers. The equivalent Swiss/French term is "calibre" and literally means much the same thing, although calibre is often used to characterise the specific layout of a movement as well as its size.
The following information is based on information in Philip Priestley's "Aaron Lufkin Dennison, An Industrial Pioneer and his Legacy".
The number 12 gives the size or diameter of the movement, followed by a • and then a 0 over a 3 that gives the pillar height which determines the thickness of the movement.
This calliper size is called the "Lancashire Watch gauge system" for determining watch sizes. Size zero formed the base of the scale with a plate diameter of 1 inch plus 5/30 inches for the mounting flange or "drop", giving a base for the scale at zero of 35 thirtieths of an inch, or 1.167″. Each 1/30 inch increased in diameter increments the gauge size by one. For smaller watches, the scale counts down from zero, indicated by 2/0, 3/0 etc. A glance at the table makes it clear.
The 12 on the Wycherley movement shown in the indicates that it is 1 inch plus (12+5)/30 = 1 and 17/30 inches in diameter, or 47/30 = 1.567″.
|10/0||26/30 = 1.000||22.0||9.75|
|9/0||27/30 = 1.000||22.9||10.1|
|8/0||28/30 = 1.000||23.7||10.5|
|7/0||29/30 = 1.000||24.6||10.9|
|6/0||30/30 = 1.000||25.4||11.3|
|5/0||31/30 = 1.033||26.2||11.6|
|4/0||32/30 = 1.067||27.1||12.0|
|3/0||33/30 = 1.100||27.9||12.4|
|2/0||34/30 = 1.133||28.8||12.8|
|0||35/30 = 1.167||29.6||13.1|
|2||37/30 = 1.233||31.3||13.9|
|4||39/30 = 1.300||33.0||14.6|
|6||41/30 = 1.367||34.7||15.4|
|8||43/30 = 1.433||36.4||16.1|
|10||45/30 = 1.500||38.1||16.9|
|12||47/30 = 1.567||39.8||17.6|
|14||49/30 = 1.633||41.5||18.4|
|16||51/30 = 1.700||43.2||19.1|
|18||53/30 = 1.767||44.9||19.9|
|20||55/30 = 1.833||46.6||20.6|
|22||57/30 = 1.900||48.3||21.4|
It might be thought odd that the gauge was based on 1/30 part of an inch rather than some less unwieldy fraction, but 1/3 of an inch was the smallest Anglo-Saxon unit of length and was called a barleycorn, because it was nominally the length of a corn or grain of barley. This measurement is still the basis for shoe sizes in Britain. When early watchmakers needed to specify dimensions more closely, it was natural for them to think in terms of 1/10 of a barleycorn.
The micrometer, with its associated division of the inch into "thous" or thousandths of an inch, was not invented until the nineteenth century. It might be thought that it would be difficult to make something as precise as a watch without a means of accurate measurement, but the first watches were made by hand finishing parts so that they all fitted together in one watch, they were not interchangeable between different watches. It was the development of accurate measuring instruments that allowed the mass production of watches, by enabling parts to be made to uniform sizes and interchangeable.
The Lancashire gauge system was adopted by American watch manufacturers, no doubt because before watches started to be manufactured in America, watches and watch movements were imported from England, and the Lancashire gauge size would have been used to specify the size of the movement, and hence the name for the size of the watch.
The gauge size is the diameter of the movement, not the size of the watch. A size 18 American railroad watch for instance should have a movement 1 + (18+5)/30 = 1.767 inches diameter, but the overall diameter of the case containing will be around 2.25″.
The 0 over 3 indicates the pillar height, the distance separating the two plates of the movement. Standard pillar height was taken 1/8″ indicated as 0/0, with increments indicated above the line and decrements below in 1/144″. So 0 over 3 indicates a pillar height of 1/8″ minus 3/144″, or 18/144 - 3/144 = 15/144, that is about 0.104″ or 2.65 mm - which when I first worked it out seemed very small, but I have just put a rule to the movement of an English lever watch that was lying on my desk and the gap between the plates is 3 mm, so 2.65 mm doesn't seem out of the question.
It seems a bit strange that the conversion between inches and millimetres is a nice easy to remember number rather than having a long string of decimal places. In fact this wasn't always so. In 1930 the British Standards Institution adopted an inch of exactly 25.4 mm, the American Standards Association followed in 1933 and by the mid 1930s many countries had adopted this "industrial inch", but these were industrial rather than legal standards. In Britain and the Commonwealth countries and America the inch was legally defined as one thirty sixth of a yard. Before 1959 the British imperial yard and the American yard were not exactly the same, and consequently British and American inches were slightly different. In 1959 the "international yard" was defined as 0.9144 metres and this was adopted in Britain and Commonwealth countries and America. The American legal inch changed by -2 millionths of an inch and the UK legal inch by +1.7 millionths of an inch, so that the inch of exactly 25.4mm falls mid way between the old UK and US legal inches.
Swiss and French watch sizes
Swiss and French watch movement sizes are usually given in lignes. A ligne (pronounced line) is a douzième or 1/12 of an old French inch, which itself is 1.0657 of an English inch. So a ligne is about 2.256mm. In the context of watches a douzième usually means a twelfth part of a ligne, also sometimes called a point. This can be measured with a douzième gauge
The standardized conversion for a ligne is 2.2558291 mm (1 mm = 0.443296 ligne), which is more easily remembered as 2.256 mm. The line size is abbreviated by a triple prime ‴ in a similar way to the double prime sign ″ for an inch.
Watches were made in sizes from 3 lignes, a very small lady's baguette movement, to 20 lignes or more for pocket watches. A typical Swiss made man's trench wristwatch from the Great War would have a movement around 12‴ or 13‴ (12 or 13 lignes) that is about 27 to 29.3 mm diameter, the case being about 32 to 35mm in overall diameter.
Copyright © David Boettcher 2006 - 2017 all rights reserved. This page updated December 2016. W3CMVS.