NTN - Plummer Blocks

mcloutiermas

Shaft Design

7. Shaft Design

7.1 Bearing-to-shaft fit

The tolerance requirements of the shaft outside

diameter differs between a bearing with an adapter and a

cylindrical bore bearing each mounted to a plummer

block. Table 7.1 summarizes the recommended bearingto-shaft

fits.

A bearing with an adapter is installed to a shaft by

means of an adapter. A cylindrical bore bearing is usually

positioned in interference fit by a shaft shoulder and

secured with a nut and washer. For this application, the

shaft is provided with threading and washer groove as

illustrated in Fig. 7.1.

Fig. 7.1

Table 7.1 Recommended bearing-to-shaft fit

Bearing bore type

Load condition

Shaft outside diameter

Self-aligning ball bearing Self-aligning roller bearing

Shaft type and

tolerance class

Remarks

Tapered bore

(complete with

adapter assembly)

Various loads

All bearing sizes

H9/IT5

The tolerance class for transmission shafts

may be h10/IT7. "IT5" or IT7" means that the

shaft form tolerance (circularity, cylidricity,

etc.) must satisfy tolerance class IT5 or IT7.

Light load and

fluctuating load

over 18, incl. 100

over 100, incl. 200

–––

–––

J6

k6

Light load essentially means a load as small

as 6 to 7% the basic dynamic load rating.

Pr0.07Cr

Cylindrical bore

Normal load

over 18, incl. 100

over 100, incl. 200

–––

–––

–––

–––

over 40, incl. 65

over 65, incl. 100

over 100, incl. 140

over 140, incl. 280

k5

m5

m6

n6

p6

Normal load is a load that satisfies

0.06CrPr0.12Cr.

Heavy load and

shock load

–––

–––

–––

over 50, incl. 100

over 100, incl. 140

over 140

n6

p6

r6

Heavy load is a load that satisfies Pr0.12Cr.

For this type of application, use a bearing

whose clearance is greater than normal

clearance.

7.2 Mounting dimensions

To be able to correctly seat a cylindrical bore bearing to

the shaft shoulder, the height and fillet radius ras of the

shoulder must be greater than the chamfering rs min of the

bearing as specified in Table 7.2.

If the bearing is used on the shaft end, the configuration

must be designed such that the shaft end does not

interfere with the face of bearing bore. For reference,

Table 7.3 provides the wall thickness values at the

bearing bore.

Table 7.2 Fillet radius and shoulder height of shaft

Unit: mm

Fillet radius

Chamfer

dimension

rs min mm

1

1,1

1,5

2

2.1

2.5

3

4

5

6

7.5

9.5

Shoulder

height h 1

(min)

2.75

3.5

4.25

5

6

6

7

9

11

14

18

22

ras max

1

1

1.5

2

2

2

2.5

3

4

5

6

8

1 The shoulder height must be greater than

that specified when the shaft is subjected to

a greater axial load.

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