Page 149 - Rollingbearings

Surface texture of bearing seats
Tolerances for • To determine the permissible dispersion of based on saddles and gauging pins. More
tapered seats the taper angle α, use practical, but less accurate measurement
methods include ring gauges, taper gauges
α = 2atan (V /2) and sine bars. For information about SKF
k
For tapered shaft seats, SKF recommends measuring devices, refer to skf.com (GRA 30
the following tolerances (ig. 6): • The roundness tolerance is deined as ring gauges and DMB taper gauges).
“distance t between two concentric circles
• The permissible deviation for the rate of in each radial plane perpendicular to the
the taper is a ± tolerance in accordance cone axis along the tapered surface of the
with IT7/2 The bearing width B is the shaft”. t is the value of tolerance grade Surface texture of
nominal size, which determines the stand­ IT5/2, based on the diameter d. Where a
ard tolerance values The permissible high degree of precision is required, IT4/2 bearing seats
deviation for the rate of the taper can be should be used instead.
determined using • The straightness is deined as “In each
axial plane through the tapered shaft, the The surface texture of a bearing seat has
tolerance zone is limited by two parallel less of an impact on bearing performance
IT7/2
k lines a distance t apart”. t is the value of compared to the dimensional and geomet­
B tolerance grade IT5/2, based on the diam­ rical tolerances of the seat. However, the
∆ =
eter d. texture of the mating surfaces affects
The permissible range of dispersion of the smoothing, which can reduce the interfer­
rate of the taper can be determined using ence in a it. The surface texture should be
Taper position limited to ensure the required it is obtained.
Guideline values for the roughness proile
IT7/2
k Only dimensional and geometrical toler­ parameter Ra are listed in table 4. These
B ances of the taper are indicated in ig. 6. The recommendations apply to ground seats,
V = 1/k ±
axial position of the taper requires additional which are normally assumed for shaft seats.
speciications. When specifying the axial For housing seats, which are normally ine­
where position, you should also take into account turned, the Ra values may be one class
Δ = the permissible deviation of the rate the axial drive­up distance of the bearing, higher. For applications where some loss of
k
of the taper which is required to achieve a suitable inter­ interference is not critical, rougher surfaces
V = the permissible range of dispersion ference it. than recommended in table 4 can be used.
k
of the rate of the taper
B = bearing width [mm] Bearing interfaces
IT7 = the value of the tolerance grade, Checking tolerances
based on the bearing width [mm]
k = factor for the taper To check whether a tapered shaft seat is
= 12 for taper 1:12 within its tolerances, SKF recommends
= 30 for taper 1:30 measuring it with a special taper gauge, B.6

Table 4 Fig. 6
Surface roughness of bearing seats Tolerances for tapered shaft seats
Seat diameter Ra (guideline values for ground seats) 1/k ± (IT7/2) / B
d, D Diameter tolerance grade IT5/2 A t
> ≤ IT7 IT6 IT5 Ra 1,6 IT5/2
A
mm μm
– 80 1,6 0,8 0,4
80 500 1,6 1,6 0,8
500 1 250 3,2 1) 1,6 1,6
d js9 E
t

B
1) When using the oil injection method for mounting, Ra should not exceed 1,6 μm.

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