why are jewel bearings present in watches?

Question

pls pls help me. be as descriptive as possible

Answer 1

*Jewel bearings were used widely for mechanical (escapement) watches, where their low and predictable friction improved watch accuracy. A typical mark of watch quality was a note such as "17 jewels". More jewel bearings often meant better precision. Some makers added non-functional or unnecessary jewels to give the impression of accuracy. Some watches had 100 jewels, most of them of no use. A typical "fully jeweled" time-only watch has two cap jewels, two pivot jewels, an impulse jewel for the balance wheel, two pivot jewels, two pallet jewels for the pallet fork, and two pivot jewels each for the escape, fourth, third and center wheels. Modern electronic watches achieve accuracy entirely separate from the friction of the mechanism, but early quartz watches used jewels to increase battery life, and high-grade quartz watches use jewels to reduce friction and wear.

Today, jewel bearings are used widely in sensitive measuring equipment.

The advantages of jewel bearings include high accuracy, very small size and weight, low friction, predictable friction including good temperature stability, ability to operate without lubrication and in corrosive environments.

*A jewel bearing is a bearing which an unlubricated metal shaft spins in a jewel-lined pivot hole. The hole is typically shaped like a donut hole and is slightly larger than the shaft diameter. In operation, the shaft tilts slightly so as to contact the jewel pivot hole at two opposite points. The shaft rolls inside of the bearing rather than sliding. As the shaft rolls, the center precesses.

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http://www.microlap.com/pdfs/Jewel_Bearings_HR.pdf
http://www.swissjewel.com/jewel_bearing_applications.htm
http://www.swissjewel.com/jewel_bearing_design_aids.htm

Answer 2

Besides what the answerer above says...

Diamonds are the hardest known substance and sapphires are right up there in hardness (an a lot cheaper). Hardness translates to longevity of a bearing.

Were the bearings made of steel, they would wear out much quicker and the watch would need repair more often.

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Answer 3

While the first answer was detailed and accurate, it was simply a copy and paste from Wikipedia, and did not cite it's source.

The actual Wikipedia article has links to additional information if desired:
http://en.wikipedia.org/wiki/Jewel_bearing