Jewel Bearing Applications
Synthetic Sapphire and Ruby, because of their hardness and ability to accept a high polish, are recognized universally as the ideal material for instruments, meters, control devices and other precision mechanisms where low friction, long life and dimensional accuracy are important.
Typical Applications: Flow Meters, Gauges, Meters, Indicators, Aircraft Instruments, Gyros, Watches, Clocks
Outstanding advantages of synthetic Sapphire Jewel Bearings
- High polish and low friction
- Hardness and Shock Resistant
- Miniature Size
- Close Tolerances, Low Cost
- Long & Accurate Wear Life
- Resistance to Heat, Corrosion, Distortion
- High Dielectric Strength
Jewel bearings are normally mounted in some type of housing. This housing may be a screw, bushing or plate fabricated from half hard brass, C.R.S., stainless, aluminum or other metals. Mounting is generally accomplished by spin setting or friction set. By this method, the jewel is forced into a hole drilled to create interference fit with the OD of the jewel.
Spin setting is the more generally used and more satisfactory mounting method because minimum pressure is applied on the jewel, and there is less danger of breakage or damage. The jewel is placed in position in the hole and setting material is spun over the edge of the jewel to hold it in place.
Spring-loaded mounts offer a factor of safety in jewel assembly and application. With rigid mountings, excessive tightening of the bearing can cause the pivot to bottom with the possibility of damage to the bearing or pivot. With spring set jewels, the bearing adjustment is not critical.
Ring Jewels serve as radical or sleeve bearings used with a straight cylindrical shaft. They offer a great flexibility in design because of the many possible combinations with endstones. Rugged straight hole rings restrict lateral movement to a minimum but require accurate alignment when the clearance between pivot and bearing is closely held. An olive hole (radiused ID) jewel offers lower friction with the pivot and permits adjustment in the assembly. A bombé face provides minimum contact with a shouldered pivot for light, intermittent end thrust. Where thrust load is continuous, an endstone is usually combined with the ring jewel.
Typical Applications: General Instrumentation, Gauges, Meters, Indicators, Watches, Clocks, Potentiometers, Gyros, Aircraft Instruments.
Vee Jewels are well suited to sensitive instruments where the moving element is light. They offer minimum friction when used with conical, small radiused pivots and permit slight lateral movement. The jewel radius should be 3 times larger than the pivot radius for low friction torque, sensitivity, and resistance to deformation. The contact area of the pivot should be highly polished and a micro-inch finish of 2 or better on the pivot radius is recommended.
Typical Applications: Ohmmeters, Voltmeters, Gauges, and other Indicating Meters; Timers and Relays.
Endstones find wide use as a thrust bearing in combination with a ring jewel which serves as the annular bearing. The endstone may be mounted in the same housing with the ring jewel or mounted separately in an adjusting screw—especially when the end of the pivot extends beyond the radical bearing. Pivot ends in both cases should be highly polished. Endstones are also used as spacers or insulators.
Typical Applications: General Instrumentation, Insulating Spacers, Time-keeping movements.
Cup Jewels are generally used with a semi-spherical pivot or in a design that fits a ball bearing between two cup jewels. They are widely used for vertical shaft applications. Typical Applications: Compasses, Heat Monitors
The shape and type of the pivot used are determined by the operating conditions, the type of jewel, and other design factors involved in suspending the moving element in the system. Cylindrical pivots can be supported by any of the ring jewel designs and combinations. End thrust may be taken by having a shoulder on the pivot ride on the polished face of the jewel or by using an endstone with the ring jewel to take the thrust from a pivot with a rounded end. Pivots with radiused conical ends are generally used with vee jewels. Rounded or semi-spherical pivots are used with single cup jewels and flat endstones. Since working areas of the jewel bearing are lapped to a mirror finish, the contact area of the pivot should be highly polished for best performance. On pointed or ball end pivots, a finish of 2 micro inch or better on the pivot radius is recommended. Through our affiliate, HERMAN D. STEEL COMPANY, we can furnish miniature pivots of most materials turned with extreme accuracy. Especially recommended is “Nivapoint”, a patented, non-corrosive, non-magnetic material with excellent tensile strength and hardness. Please consult us on your pivot requirements.