Jeweled bearings use a metal spindle with a jewel lined pivot hole (pictured below). They have been important in the manufacture of mechanical timepieces since the early 1700's. Their importance lies in the fact that they can be machined to very high accuracy, they have low and predictable friction, and their hardness gives them very low wear. They are known for operating in sealed environments for decades with no servicing.

With the advent of synthetic crystal manufacturing in the early 1900's jeweled bearings became the standard for every important bearing in mechanical timepieces. Every quality mechanical watch manufactured these days, for instance, has at least 17 jeweled bearings for the 'going train'.

$\hspace{150px}$Jeweled bearing from wikimedia commons

My questions are:

  • Are there any other common applications for jeweled bearings besides mechanical timepieces?
  • If so, what are the largest jeweled bearings used for?

Typically jewel bearings (as you've described) are not used in large scale industrial equipment. The main reason jewel bearings are used is their inherent hardness. The bearing material has very little wear over the life of the bearing. Most of the wear occurs to the shaft riding in the bearing.

In industry, you typically want to avoid wearing the shafting under any circumstance. An example is power generation turbine shafting. The turbine shaft will typically ride in a journal bearing in which the journal is hydrodynamically lubricated via forced lubrication. The bearing material is normally made of a softer material than the shaft. Under normal operations the shaft rides on a thin film of oil, separating it from the bearing material. In the event of a loss of lubrication or a breakdown of the oil film, the shaft will contact the bearing material. Since it is typically much easier and less costly to replace damaged bearing material versus replacing an entire turbine shaft and rebalancing said shaft, the bearings are normally designed such that the bearing material is sacraficial. When the hard shaft material contacts the soft bearing material, the bearing material will heat up and be wiped away instead of scoring the shaft. A jewel bearing would do the opposite, scoring and wearing the shaft.

Other applications of jewel bearings, aside from watch movements, include gyroscopes, turbine flow meters, and other assemblies which are typically subjected to small loads and do not generate large amounts of heat which require might forced lubrication to remove the heat.



"The business part of a compass is out of sight. This is a set of tiny magnets glued under the compass card and surrounding the jeweled pivot that supports the center of the card." -The Annapolis Book of Seamanship, by John Rousmaniere


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