# Tolerances for tapered seats

For tapered shaft seats, SKF recommends the following tolerances (fig. 1):
• The permissible deviation for the rate of the taper is a ± tolerance in accordance with IT7/2. The bearing width B is the nominal size, which determines the standard tolerance values. The permissible deviation for the rate of the taper can be determined using

The permissible range of dispersion of the rate of the taper can be determined using

where
 Δk the permissible deviation of the rate of the taper Vk the permissible range of dispersion of the rate of the taper B bearing width [mm] IT7 the value of the tolerance grade, based on the bearing width [mm] k factor for the taper 12 for taper 1:12 30 for taper 1:30

• To determine the permissible dispersion of the taper angle α, use

α = 2atan (Vk/2)

• The roundness tolerance is defined as "distance t between two concentric circles in each radial plane perpendicular to the cone axis along the tapered surface of the shaft". t is the value of tolerance grade IT5/2, based on the diameter d. Where a high degree of precision is required, IT4/2 should be used instead.
• The straightness is defined as “In each axial plane through the tapered shaft, the tolerance zone is limited by two parallel lines a distance t apart”. t is the value of tolerance grade IT5/2, based on the diameter d.

## Taper position

Only dimensional and geometrical tolerances of the taper are indicated in fig. 1. The axial position of the taper requires additional specifications. When specifying the axial position, you should also take into account the axial drive-up distance of the bearing, which is required to achieve a suitable interference fit.

## Checking tolerances

To check whether a tapered shaft seat is within its tolerances, SKF recommends measuring it with a special taper gauge, based on saddles and gauging pins. More practical, but less accurate measurement methods include ring gauges, taper gauges and sine bars. For information about SKF measuring devices refer to GRA 30 ring gauges and DMB taper gauges.