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Similar comparisons of the radial deflection characteris- tics of the same two types of angular-contact ball bearings can be made from the two graphs shown in Figure 14. These curves show that increased radial deflections result when bearings having the higher contact angle are used. The indicated radial deflections are for one bearing. When employing duplex pairs of bearings under equal, applied loads, the radial deflections would be approxi- mately one-half of the values shown.

EFFECT OF CONTACT ANGLE ON RADIAL DEFLEC- TION

Less Radial Rigidity High Contact Angle

Radial Deflection

.0014

.0012

.0010

.0008

.0006

.0004

.0002

100

200

300

400

500

600

700

Radial Load – lbs. B LIGHT PRELOAD 40 LBS. C MEDIUM PRELOAD 125 LBS. D HEAVY PRELOAD 250 LBS.

Less Radial Rigidity High Contact Angle

Radial Deflection

.0014

.0012

.0010

.0008

.0006

.0004

.0002

100

200

300

400

500

600

700

Radial Load – lbs. B LIGHT PRELOAD 40 LBS. C MEDIUM PRELOAD 125 LBS. D HEAVY PRELOAD 250 LBS.

Figure 14 – Radial Deflections

Width Tolerances

The width tolerance for individual inner and outer rings is shown on pages E4, E5 but, to allow for the face grinding on two bearings for various preloads, the total width tolerances of duplex pairs of bearings are as follows:

Over

Inclusive

Maximum

Minimum

0

200

.000"

.010"

.00mm

.25mm

Nominal bore

Width

Millimeters

Tolerance

102800

B

C D

B C

D

ENGINEERING

If other than a pair of bearings is involved, the total width tolerance is in proportion to the number of bearings. If closer than standard width tolerances are required specify by adding FS732 as a suffix to the part number.

Recommended Shaft and Housing Tolerances Shaft Fits

The main purpose of the shaft fit is to assure a proper attachment of the inner ring to the shaft. Under normal conditions of shaft rotation, a loosely fitted inner ring will creep on the shaft, leading to wear and peening. This condition will be further aggravated by increase of load or speed. To prevent creeping or slipping, the inner ring should be mounted firmly in place and held securely against the shaft shoulder. However, it is important that the shaft fit should not result in any undue tightening of the bearing. An excessive tension would be established in the ring, resulting in a proportionate expansion which would disturb the internal fit of the bearing and lead to heating and increased power consumption.

As a general rule, it is recommended that the shaft size and tolerance for seating superprecision bearings (ABEC-7 and 9) be the same as the bearing bore. In the case of preloaded bearings, the ideal shaft fit to strive for is line-to- line fit, since an excessively tight fit expands the bearing inner ring and increases the bearing preload which can lead to over-heating. For example, a duplex pair of 2MM9111WI- DUL bearings, with 35 pounds built-in preload, when mounted on a shaft that provides an interference fit of .0004 inch, will increase the preload to approximately 180 pounds which could result in elevated operating temperatures.

EXAMPLE: ABEC 7

Bore size

Shaft Diameter

Inches

Inches

max. 2.1654

min. 2.1652

Resulting Mounting Average Fit Fit, Inches

line-to-line

min. 2.1652

.0002 loose

max. 2.1654

.0002 tight

EXAMPLE: ABEC 9

Bore size

Inches max. 2.16540

Shaft Diameter

Inches min. 2.16525

Resulting Mounting Average Fit Fit, Inches

.00015 loose

line-to-line

min. 2.16525

max. 2.16540

.00015 tight

Housing Fits

Under normal conditions of rotating shaft, the outer ring is stationary and should be mounted with a hand push to a light tapping fit. Should the housing be the rotating member, the same fundamental considerations apply in mounting the outer race as in the case of an inner ring mounted on a rotating shaft.

As a general rule, the minimum housing bore dimen- sion for superprecision bearings (ABEC-7 and 9) may be established as the same as the maximum bearing outside diameter. If the bearing O.D. tolerance is .0003 inch (.0008mm), the maximum housing bore should be established as .0003 inch (.0008mm) larger than the minimum housing bore dimensions.

E33

ENGINEERING

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