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2021-04-11T19:42:19Z

1 revision imported: Mitul Imported from Wikipedia

setup>Chetvorno: /* Characteristics */ Rewrote sentence on lubrication to replace unencyclopedic language (WP:TONE)

2021-01-24T21:17:38Z

Characteristics: Rewrote sentence on lubrication to replace unencyclopedic language (WP:TONE)

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{{more citations needed|date=March 2011}}
[[Image:Chinese movement escapement and jewels.jpg|thumb|275px|right|Ruby jewel bearings used for a balance wheel in a mechanical watch movement.]]
[[Image:Watch jewel bearing.svg|thumb|275px|Cross-section of a jewel bearing in a mechanical watch. This type of donut-shaped bearing (red) is called a ''hole jewel'', used for most of the ordinary wheels in the gear train. It is usually made of synthetic sapphire or ruby, press-fit into a hole in the movement's supporting plate (grey). The cup-shaped depression in the top of the jewel is the oil cup; its purpose is to hold the lubricating oil (yellow) in contact with the bearing shaft by capillary action.]]
[[Image:Watch jewel bearing and capstone.svg|thumb|275px|In wheels where friction is critical, a ''capstone'' is added on the end to prevent the shoulder of the shaft from bearing against the face of the jewel.]]

A '''jewel bearing''' is a [[plain bearing]] in which a metal [[spindle (tool)|spindle]] turns in a [[gemstone|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]], usually either [[synthetic sapphire]] or [[Ruby#Synthetic and imitation rubies|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 watch]]es.

==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]], [[sapphire]], [[ruby]], and [[garnet]]. In 1902, [[Verneuil process|a process]] to make synthetic sapphire and ruby (crystalline [[aluminium oxide]], also known as [[corundum]]) 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.<ref name="elgin">{{cite web
| last = Elgin National Watch Company
| first =
| author-link =
| title = Jewel Bearings
| work =
| publisher = Paul Hance Productions, Inc.
| date =
| url = https://elginnationalwatches.com/elgin-jewel-bearings/
| format =
| doi =
| accessdate = 2019-01-10}}</ref> Modern jewel pivots are often made using high-powered lasers, chemical [[industrial etching|etching]], and ultrasonic [[milling machine|milling]].

During [[World War II]] jewel bearings were one of the products restricted by the United States government [[War Production Board]] as critical to the war effort.<ref name="elgin1">{{cite web
| last =
| first =
| author-link =
| title = Preparage – Jewel Bearings
| work =
| publisher = elginnationalwatches.com
| date =
| url = https://elginnationalwatches.com/jewel-bearings-preparage/
| format =
| doi =
| accessdate = 2019-01-10}}</ref>

==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 [[Friction#Kinetic friction|kinetic friction]] and highly consistent [[Friction#Static friction|static friction]].<ref name="Baillio" >{{cite web
| last = Baillio
| first = Paul
| author-link =
| title = Jewel bearings solve light load problems
| work =
| publisher = Bird Precision
| date =
| url = http://www.birdprecision.com/PDFs/jewelbearings.pdf
| format =
| doi =
| accessdate = 2008-07-16}}</ref> The [[Stiction|static coefficient of friction]] of brass-on-steel is 0.35, while that of sapphire-on-steel is 0.10–0.15.<ref name="Baillio" /><ref>{{cite web
| last = Hahn
| first = Ed
| author-link =
| title = Coefficients of friction for various horological materials
| work = TZ Classic Forum
| publisher = TimeZone.com
| date = January 31, 2000
| url = http://www.timezone.com/2002/09/28/coefficients-of-friction-for-various-horological-materials
| format =
| doi =
| accessdate = 2018-08-02}}</ref> Sapphire surfaces are very hard and durable, with [[Mohs scale of mineral hardness|Mohs hardness]] of 9 and [[Knoop hardness test|Knoop hardness]] of 1800,<ref>{{cite web
| last =
| first =
| author-link =
| title = Synthetic Ruby and O-Rings
| work =
| publisher =
| date =
| url = http://www.oringsusa.com/html/synthetic_ruby.html
| doi =
| accessdate = 2013-06-01}}</ref> and can maintain smoothness over decades of use, thus reducing friction variability.<ref name="Baillio" /> 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.<ref>BHI</ref>

==Uses==
The predominant use of jewel bearings is in [[mechanical watch]]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]], 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 [[crystal oscillator|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 [[galvanometer]]s, [[compass]]es, [[gyroscope]]s, [[gimbal]]s, [[Indicator (distance amplifying instrument)|dial indicators]], [[Calipers|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]], although they are made as large as 10 mm and may support loads up to about 500 g.<ref name="Baillio" /> Their use has diminished with the popularization of digital measuring instruments.

== See also ==
* [[Incabloc shock protection system]]
* The [[Clock of the Long Now]] which will use ceramic bearings with no lubrication at low speed

==References==
* {{cite book
| first = G. H.
| last = Baillie
| title = Watchmakers And Clockmakers Of The World
| edition = 2e
| publisher = Nag Press
| year = 1947
}}

==Footnotes==
{{reflist}}

==External links==
*[http://www.birdprecision.com/PDFs/jewelbearings.pdf Paul Baillio, "Jewel Bearings Solve Light Load Problems"] ([[Portable Document Format|PDF]])
*[http://www.birdprecision.com/PDFs/design_factors.pdf A. C. Lawson, "Design Factors for Jewel Bearing Systems"] (PDF)
*[http://www.birdprecision.com/PDFs/frictional_losses.pdf R. H. Warring, "Calculating Frictional Losses in Jewel Bearing Movements"] (PDF)
*[http://www.awci.com/ American Watchmakers-Clockmakers Institute]
*[https://web.archive.org/web/20050428060333/http://www.timezone.com/library/workbench/workbench0025/ TimeZone.com discussion of watch jeweling]
*[https://monochrome-watches.com/technical-perspective-jewel-bearings-watch-movement-rubies ''Monochrome-watches, What are jewel bearings, Xavier Markl'']
*[https://elginnationalwatches.com/elgin-jewel-bearings/ ''Jewel Bearings: A Presentation of the Elgin National Watch Company'']
*[https://www.industrialjewels.com/jewel-bearing/ ''Jewel Bearing is made from synthetic ruby or sapphire materials'']

{{DEFAULTSORT:Jewel Bearing}}
[[Category:Bearings (mechanical)]]
[[Category:Timekeeping components]]

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setup>Chetvorno: /* Characteristics */ Rewrote sentence on lubrication to replace unencyclopedic language (WP:TONE)