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What is the tolerance for the contact angle between steel balls and raceways?

For single-row ball slewing bearing, the contact angle (typically 45°) does not have a globally standardized, absolute-value tolerance specification (e.g., requiring it to be 45° ± ?°).

This is because the contact angle is a derived dimension or indirectly guaranteed dimension. It is not controlled by directly machining an angle, but rather indirectly ensured by precisely controlling the dimensions and tolerances of the following two core parameters:

1.Groove curvature radius

2.Ball diameter

We typically ensure the contact angle remains within the ideal range by controlling the dimensional fit relationship between the raceway and the ball.

Groove curvature radius ratio: Typically, the ratio of the groove curvature radii (r_i, r_o) of the inner and outer raceways to the ball diameter (D_w) is maintained between 0.52 and 0.54 (i.e., r ≈ 0.53 * D_w). This ratio directly determines the theoretical contact angle of 45°.

Dimensional Tolerance:Extremely stringent tolerances (typically at the micrometer level) are specified for the diameter of the raceways, the groove curvature radius, and the diameter of the steel balls. The cumulative effect of these tolerances ultimately manifests as variations in the contact angle.

Under ideal manufacturing and fit conditions, the contact angle will be very close to 45°. Actual deviations are usually minimal, typically varying only within a range of a few tenths of a degree to one or two degrees. However, this value is generally not used as a direct inspection criterion but rather as an outcome of process control.

If you need to specify requirements in drawings or technical agreements, it is usually unnecessary to directly mark “contact angle tolerance.” Instead, specify the dimensional tolerances of the raceway, shape tolerances (roundness, profile), and the precision grade of the steel balls.