Blog: Jewels in watch movements
Date: 16 February 2016Copyright © David Boettcher 2006 - 2017 all rights reserved.
I make additions and corrections to this web site frequently, but because they are buried somewhere on one of the pages the changes are not very noticeable, so I decided to create this blog section to highlight new material. Here below you will find part of one of the pages that I have either changed or added to significantly.
The section below about jewels in watch movements is from my page about watch movements.
If you have any questions or comments, please don't hesitate to contact me via my Contact me page.
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Jewel watch bearings were originally made from real gem stones, rubies and diamonds, hence the name "jewel".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.
Copyright © David Boettcher 2006 - 2017 all rights reserved. This page updated February 2016. W3CMVS.