Jewel Bearing
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A jewel bearing is a plain bearing in which a metal spindle turns in a jewel-lined pivot hole. The hole is typically shaped like a torus and is slightly larger than the shaft diameter. The jewels are typically made from the mineral
corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the ...
, usually either synthetic sapphire or synthetic ruby. Jewel bearings are used in precision instruments where low friction, long life, and dimensional accuracy are important. Their largest use is in mechanical watches.


History

Jewel bearings were invented in 1704 for use in watches by Nicolas Fatio de Duillier, Peter Debaufre, and Jacob Debaufre, who received an English patent for the idea. Originally natural jewels were used, such as
diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...
, sapphire,
ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapp ...
, and
garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different ...
. In 1902, a process to make synthetic sapphire and ruby (crystalline aluminium oxide, also known as
corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the ...
) was invented by
Auguste Verneuil Auguste Victor Louis Verneuil (; 3 November 1856 – 27 April 1913) was a French chemist best known for inventing the first commercially viable process for the manufacture of synthetic gemstones. In 1902 he discovered the "flame fusion" process, ...
, making jewelled bearings much cheaper. Today most jewelled bearings are synthetic ruby or sapphire. Historically, jewel pivots were made by grinding using diamond abrasive. Modern jewel pivots are often made using high-powered lasers, chemical
etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other type ...
, and ultrasonic
milling Milling may refer to: * Milling (minting), forming narrow ridges around the edge of a coin * Milling (grinding), breaking solid materials into smaller pieces by grinding, crushing, or cutting in a mill * Milling (machining), a process of using rota ...
. During
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
jewel bearings were one of the products restricted by the United States government
War Production Board The War Production Board (WPB) was an agency of the United States government that supervised war production during World War II. President Franklin D. Roosevelt established it in January 1942, with Executive Order 9024. The WPB replaced the S ...
as critical to the war effort.


Characteristics

The advantages of jewel bearings include high accuracy, very small size and weight, low and predictable friction, good temperature stability, and the ability to operate without lubrication and in corrosive environments. They are known for their low kinetic friction and highly consistent static friction. The static coefficient of friction of brass-on-steel is 0.35, while that of sapphire-on-steel is 0.10–0.15. Sapphire surfaces are very hard and durable, with Mohs hardness of 9 and Knoop hardness of 1800, and can maintain smoothness over decades of use, thus reducing friction variability. Disadvantages include brittleness and fragility, limited availability/applicability in medium and large bearing sizes and capacities, and friction variations if the load is not axial. Like other bearings, most jeweled pivots use oil lubrication to reduce friction.BHI


Uses

The predominant use of jewel bearings is in mechanical watches, where their low and predictable friction improves watch accuracy as well as improving bearing life. Manufacturers traditionally listed the number of jewels prominently on the watch face or back, as an advertising point. A typical ''fully jeweled'' time-only watch has 17 jewels: two cap jewels, two pivot jewels and an impulse jewel for the balance wheel, two pivot jewels and two pallet jewels for the pallet fork, and two pivot jewels each for the escape, fourth, third, and center wheels. In modern quartz watches, the timekeeper is a quartz crystal in an electronic circuit, powering a small stepper motor. Because of the small amount of torque needed to move the hands, there is almost no pressure on the bearings and no real gain by using a jewel bearing, hence they are not used in a large proportion of quartz movements. The other major use of jeweled bearings is in sensitive mechanical measuring instruments. They are typically used for delicate linkages that must carry very small forces, in instruments such as galvanometers,
compass A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
es, gyroscopes, gimbals, dial indicators, dial calipers, and turbine flow meters. In such instruments, jewel bearings are often used as pivots for their needles which need to move reliably and with low variability even when measuring small changes. Bearing bores are typically smaller than 1 mm and support loads weighing less than 1
gram The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to ...
, although they are made as large as 10 mm and may support loads up to about 500 g. Their use has diminished with the popularization of digital measuring instruments.


See also

*
Incabloc shock protection system The Incabloc shock protection system is the trade name for a spring-loaded mounting system for the jewel bearings that support the balance wheel in a mechanical watch, to protect the wheel's delicate pivots from damage in the event of physical s ...
* The Clock of the Long Now which will use ceramic bearings with no lubrication at low speed


References

*


Footnotes


External links


Paul Baillio, "Jewel Bearings Solve Light Load Problems"
( PDF) *broken lin
A. C. Lawson, "Design Factors for Jewel Bearing Systems"
(PDF)
R. H. Warring, "Calculating Frictional Losses in Jewel Bearing Movements"
(PDF)
American Watchmakers-Clockmakers Institute

TimeZone.com discussion of watch jeweling''Monochrome-watches, What are jewel bearings, Xavier Markl''''Jewel Bearings: A Presentation of the Elgin National Watch Company''''Jewel Bearing is made from synthetic ruby or sapphire materials''
{{DEFAULTSORT:Jewel Bearing Bearings (mechanical) Timekeeping components