High precision bearings must guide machine parts with very high precision and support forces at up to very high speeds. They are selected predominantly from the perspectives of

• accuracy
• rigidity
• running behaviour.

In order that they can fulfil these tasks for as long as possible,
the bearings must run without wear. The precondition for this is the creation of a load-bearing hydrodynamic lubricant film at the contact points of the rolling contact partners. Under these conditions, rolling bearings will achieve their fatigue life in a large number of applications. If the design is appropriate to the fatigue life, the operating life of the bearing is normally restricted by the lubricant operating life.

The decisive factors for the operating life from the perspective of load are the Hertzian pressures occurring at the contacts and the bearing kinematics. For high performance assemblies, individual design with the aid of special calculation programs is therefore advisable.

Since failure as a result of fatigue plays no part in practice in the case of high precision bearings, calculation of the rating life L₁₀ in accordance with DIN ISO 281 is not suitable as a means of determining the operating life.

For bearings under static loading, the following applies:

In order to maintain the accuracy of the bearings, a static load safety factor S₀ ＞ 3 is required.

The speeds of the bearing arrangements are dependent on:

• the preload of the bearings
• the elastic or rigid arrangement of the bearings in the spindle
• mounting as single bearings or in pairs
• the lubricants
• the cooling of the bearings.

The speeds stated in the dimension tables are guide values for single bearings under elastic preload and low loads.

The limiting speeds n_G given in the dimension tables are valid for lubrication with grease or minimal quantity lubrication with oil and must not be exceeded.

For a more detailed description, see Catalogue AC 41 130,
Super Precision Bearings.

Universal bearings of the same sort (same bore and outside diameter) are also available as sets. They can be used in any arrangement (O, X, tandem), Figure 1 to Figure 3.

Sets with slight preload have the following designations:

• duplex (2 bearings), suffix DUL
• triplex (3 bearings), suffix TUL
• quadruplex (4 bearings), suffix QUL.

When ordering bearings, the number of sets must be stated, not the number of single bearings.

In ready-to-fit bearing sets, the bearings are supplied for use in a specifically defined arrangement.

The bearings must be fitted in the arrangement ordered.

1-HSS7012-C-T-P4S-DBL Description: two spindle bearings in O arrangement, slight preload.

For spindle bearings, fits are recommended as a function of the speeds, see Catalogue AC 41 130, Super Precision Bearings.

The bearing tables give the maximum dimensions of the radii r_a and r_a1 and the diameters of the abutment shoulders D_a and d_a.