Ring Jewel and Endstones

Ring jewels are miniature types of annular or journal type bearings. Typical materials are synthetic sapphire and ruby with friction of .15 or less (sliding friction against steel). Because there is no detent to overcome, as is found in miniature ball races, starting torque is extremely low. This type of bearing relies on line contact with the shaft. The shaft is usually a hardened alloy of RC45 or greater with high surface finish for best frictional performance. Up to three degrees of radial misalignment can be accommodated by using an olive shaped profile.(See fig. 2) Because these bearings are low cost, designers can use them at a number of points in an instrument to make a cumulative difference in frictional performance. There are a large variety of sizes available. Typical sizes are .012 through .187 I.D., .040 through .325 O.D. Concentricity is generally .0002. Ring jewels are usually used in conjunction with an end bearing for taking up thrust loads or with a shouldered shaft utilizing a bombe crowned ring jewel.

Typical applications are gear chains, linkages, timing mechanisms, counters, altimeters, gimbals suspensions, dial indicators, turbine flow devices, miniature oscillating instruments, moving coil instruments and sliding output arms.

Figure 1.

Figure 2.