Caution 1

When establishing shaft or housing sizes the effect of differential thermal expansion must be taken into account. If thermal gradients are present or dissimilar materials are used, room temperature fits must be adjusted accordingly. Approximate thermal coefficients for common materials are available from NHBB.

Caution 2

When miniature and instrument bearings are interference fitted (either intentionally or as a result of thermal gradients) the bearing radial play is reduced by an amount equal to approximately 80% of the actual diametral interference fit. Thus:

• Radial play = .0002"
• Tolerance interference fit = .0003T
• 80% of interference fit = (.0003 x .8) = .00024"
• Resultant operational radial play = (-.00004) tight

The bearing will be subject to early failure in most applications because it may already be overloaded. This problem can be solved either by a higher radial play or looser fit.

Caution 3

If the outer ring or inner ring face will be clamped or abutted against a shoulder, make sure the shoulder configuration provides a good mounting surface:

• The shoulder face must be perpendicular to the bearing mounting diameter within .0002 inches per inch.
• The corner between the mounting diameter and the face must have either an undercut or a fillet radius no larger than that shown on the table pages under the column “r”.
• The shoulder diameter must conform to this table .

Caution 4

It is relatively easy to damage a miniature and instrument bearing during assembly simply by exceeding its load capacity. Adequate fixturing must be provided for handling and assembling precision bearings to ensure that:

• When assembling the bearing to the shaft, force is applied only to the inner ring.
• When assembling into the housing, force is applied only to the outer ring.
• Any movement or shock loads which would be transmitted through the bearing are eliminated.