Friction is the enemy of the watch movement as watches are required to work on a scale that most of us can not even comprehend. When manufacturing pivots for train wheels and balance staffs, tolerances are generally 5 microns either side of the actual number. Five microns is equal to 0. Yes, of one millimeter. So reducing friction is necessary to ensure top performance for a watch movement. And this is done by setting such watch components in bearing jewels instead of having metal rub metal.
The jewels that we use in watches today and decades past are synthetic, the most common being synthetic ruby. These jewels are grown in a controlled environment as something called a boule , the French word for a cone-shaped chunk of the material. The ruby jewels must then be milled, sawed, and polished into the desired shapes, which is time-consuming and difficult, necessitating the use of diamond-tipped tools.
Where the natural rubies would have impurities called inclusions that made them difficult to work with as a bearing jewel, when grown in a laboratory setting inclusions do not occur: the grain in the jewel is minimal and they can be polished to a very high standard.
On the Mohs scale of hardness both synthetic and natural rubies rate at 9. Diamond is the hardest material on the Mohs scale, coming in at a rating of 10, making synthetic rubies a logical, cost-effective choice as a bearing jewel. Jewels today are friction-fit into main plates and bridges, however that process only began around the s.
The great disadvantage with this style of jewel setting is the time and effort needed to replace them. Modern friction fit jewels are just pressed in and out with ease, but with a rubbed-in jewel great care and time must be taken to burnish the new setting.
Contemporary watches utilize jewels in a variety of areas, including as pivot bearings for wheels, automatic winding components, and calendar mechanism as well as pallet stones. The gear train wheels of a watch are the means of transmitting power from the mainspring to the escapement. In order to make that process as efficient and friction free as possible, jewels are used as bearings for the pivots of those wheels. Steel or brass bearings would cause excessive friction, thus consuming unnecessary power from the mainspring.
The use of jewels in combination with the highly polished steel of the pivots drastically reduces that friction. Balance pivots use jeweled bearings, though their setup is slightly different: they utilize a standard-style train wheel jewel bearing except that it has metal seating around it. That metal seating holds another jewel in place that is positioned on top of the balance pivot, keeping the lubrication for the jewel in place but also greatly reducing friction.
Watches of a higher quality, such as those receiving C. C certification or higher are manufactured to a higher level of precision. One area this particular aspect stands out is the spring barrel.
Traditionally, barrels would have brass bushings as bearings for their arbors on the main plate and barrel bridge. However, a watch manufactured to a higher tolerance would swap those out for jeweled bearings. You will see in the photos that the movement is labeled 39 Jewels using a placard which was attached over top of the original label of 17 Jewels and you will find all 22 extra jewels installed in the reversers where they serve no functional purpose 11 in each reverser.
So what makes a jewel functional? The balance wheel of the watch is the most critical component of the watch for timekeeping.
Balances are fit with a different style of a jewel than most of the other wheels gears in the watch. The balance rotates back and forth on an axle known as a balance staff. The pivots of the staff are supported by a system of capped jewels in a shock system.
In a capped jewel system the pivot passes through a jewel with a hole and the tip contacts a flat jewel. This system provides the same benefits as any other jewel, mainly reducing friction and wear, but it also provides an extra advantage of being able to equalize the effects of friction between horizontal and vertical positions. That is to say when the watch face is vertical the balance wheel is exposed to the same amount of friction as when the watch face is horizontal.
This helps the watch keep better time. These are 4 of the jewels you would find in a 7 jewel pocket watch and in every modern watch.
The escapement is the mechanism which delivers energy to the balance and keeps it oscillating so the watch will run. The Swiss lever escapement, used in most modern watches is a beautiful mechanism but it has some downsides, namely friction.
This is why the co-axial escapement is considered to be a superior design because it eliminates the sliding friction of the escapement. There are 3 essential jewels in the escapement. They are a roller jewel which is attached to the roller on the balance and two pallet stones that receive the impulse from the escape wheel. The roller jewel is the part that receives the impulse from the pallet fork. It is made from ruby to keep it from developing a flat spot due to the repeated impacts at least , per day.
These are the other 3 jewels in a 7 jewel pocket watch. In the photo of the escapement, you will notice that the pivot of the pallet fork arbor is also supported in jewels. These would be brass bushings in a 7 jewel watch but are usually jewels in all modern watches.
The jewels in the gear train all share similar properties. The bottom of the jewel is flat. It has a hole drilled in it and the top has an oil sink or little bowl to hold the lubrication. Occasionally the train wheels will have capped jewels like the balance but usually they just have one jewel on each side, like the one pictured on the pallet fork.
Two jewels for each of the wheels in the train escape wheel, fourth wheel, third wheel, and center wheel will bring the count to A high-grade pocket watch with 23 jewels would have capped jewels on the escape wheel and jewels for the barrel arbor and barrel contributing 6 additional jewels. The automatic winding mechanism often takes more abuse than the escapement so jewels are really important, however, some brands have released watches without any jeweled bearings in the automatic mechanism.
This is far less common today than it was 25 or 30 years ago. The typical modern automatic watch has 17 jewels in the base movement and additional jewels in the automatic mechanism. The location and total count depends on the design.
If the automatic mechanism has an oscillating weight with an axle, like many Rolex calibers, then the axle is usually supported by two jewels. By , when Verneuil died at age 57, his process was being used to make 10 million carats of rubies annually.
In Jan Czochralski, a Polish chemist, invented a process for growing single crystals that was fast and inexpensive. It produces flawless crystals that are so clear they can easily be mistaken for glass imitations. Consequently, gemmologists now look for inclusions to distinguish natural rubies and the Czochralski process is used to manufacture rubies for industrial use. The picture here is a scan of a page from an Electa catalogue dated 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. The extra charge for 21 red rubies set in chatons is The Francs work out at 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. Jewelling reduces the wear, and thereby prolongs the life of a watch, but it also increases cost. The reduction in wear is a result of reduced friction. Variations in friction at 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. The balance staff also rotates a lot more than any wheel in the train.
It is no coincidence that the balance staff pivots were the first to be jewelled. The image here shows a balance staff in green with the balance in mustard yellow. The balance staff pivots turn in the red jewel bearings with holes through their centres, like the pivots of other train wheels. At both ends of the balance staff are red flat jewels without holes. These are end stones, sometimes called cap jewels. The use of end stones achieves two beneficial results. The first is that combined with the jewel hole they form an oil reservoir, the second is that they control the end float of the arbor.
Because the end float of the arbor is controlled by the end stone it does not need a square shoulder, so it can be made "conical", a shape that 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. Some movements have end stones 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 were made as fine as those of a balance staff to minimise friction, a downside of this would be that they were as fragile and prone to breakage as the pivots of the balance staff itself. However, the escape wheel turns much more slowly than the oscillating 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. 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.
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