Jewel Bearing
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A jewel bearing is a
plain bearing A plain bearing, or more commonly sliding contact bearing and slide bearing (in railroading sometimes called a solid bearing, journal bearing, or friction bearing), is the simplest type of bearing, comprising just a bearing surface and no roll ...
in which a metal
spindle Spindle may refer to: Textiles and manufacturing * Spindle (textiles), a straight spike to spin fibers into yarn * Spindle (tool), a rotating axis of a machine tool Biology * Common spindle and other species of shrubs and trees in genus ''Euony ...
turns in a jewel-lined pivot hole. The hole is typically shaped like a
torus In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle. If the axis of revolution does not tou ...
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 pres ...
, usually either
synthetic sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphi ...
or
synthetic 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 sap ...
. Jewel bearings are used in precision instruments where low friction, long life, and dimensional accuracy are important. Their largest use is in
mechanical watch A mechanical watch is a watch that uses a clockwork mechanism to measure the passage of time, as opposed to quartz watches which function using the vibration modes of a piezoelectric quartz tuning fork, or radio watches, which are quartz wat ...
es.


History

Jewel bearings were invented in 1704 for use in watches by
Nicolas Fatio de Duillier Nicolas Fatio de Duillier (also spelled Faccio or Facio; 16 February 1664 – 10 May 1753) was a mathematician, natural philosopher, astronomer, inventor, and religious campaigner. Born in Basel, Switzerland, Fatio mostly grew up in the then- ...
, Peter Debaufre, and Jacob Debaufre, who received an English patent for the idea. Originally natural jewels were used, such as
diamond Diamond is a Allotropes of carbon, 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 Chemical stability, chemically stable form of car ...
,
sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...
,
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 sa ...
, 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 s ...
. 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 pres ...
) was invented by Auguste Verneuil, 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 types ...
, and ultrasonic milling. 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 vast majority of the world's countries—including all of the great powers—forming two opposin ...
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 Sup ...
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 Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...
and highly consistent
static friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...
. 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 The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...
of 9 and
Knoop hardness The Knoop hardness test is a microhardness test – a test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for testing purposes. A pyramidal diamond point is pressed i ...
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 watch A mechanical watch is a watch that uses a clockwork mechanism to measure the passage of time, as opposed to quartz watches which function using the vibration modes of a piezoelectric quartz tuning fork, or radio watches, which are quartz wat ...
es, 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 A balance wheel, or balance, is the timekeeping device used in mechanical watches and small clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a ...
, two pivot jewels and two pallet jewels for the
pallet fork The pallet fork is a component of the lever escapement of a mechanical watch. The pallet fork and the lever form one component that sits between the escape wheel and the balance wheel. Its purpose is to lock the escape wheel, and release it one t ...
, and two pivot jewels each for the escape, fourth, third, and center wheels. In modern quartz watches, the timekeeper is a
quartz crystal Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
in an electronic circuit, powering a small
stepper motor A stepper motor, also known as step motor or stepping motor, is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any pos ...
. 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
galvanometer A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely. A galvanom ...
s,
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,
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...
s,
gimbal A gimbal is a pivoted support that permits rotation of an object about an axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be used to allow an object mounted on the innermost gimbal to remain independent of ...
s, 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 Physical unit, 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 wate ...
, 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
Clock of the Long Now The Clock of the Long Now, also called the 10,000-year clock, is a mechanical clock under construction that is designed to keep time for 10,000 years. It is being built by the Long Now Foundation. A two-meter prototype is on display at the Sci ...
which will use ceramic bearings with no lubrication at low speed


References

*


Footnotes


External links


Paul Baillio, "Jewel Bearings Solve Light Load Problems"
(
PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...
) *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