ABMA 7:1995(S2013) pdf download

ABMA 7:1995(S2013) pdf download.Shaft and Housing Fits for Metric Radial Ball and Roller Bearings (Except Tapered Roller Bearings) Conforming to Basic Boundary Plan
1. Scope
This standard covers the general selection of shaft and housing fits for metric radial ball and roller bearings of tolerance classes ABEC 1 – RBEC 1 as influenced by the type and extent of bearing loading and other design requirements. Other tolerance classes are not covered by this standard. Recommendations for the fitting practices of some particular types of ball and roller bearings are covered in other ANSI/ABMA standards. These include:This standard can also be used as a guide for determining shaft and housing dimensions for inch design ball and roller bearings by using the recommended shaft and housing fits for metric bearings and applying the appropriate bore and O.D. tolerances for the inch design bearings, except those bearings covered by ANSI/ABMA Standard 15.
2. Conformity with
Other ANSI Standards In the size range 0-2500 mm, the deviations used in this standard for shaft and housing seats conform to American National Standard ANSI B4.2, “Preferred Metric Limits and Fits”.
3. Description of Shaft and Housing
Tolerance Classifications In the size range described in 2 above, the tolerance classifications are designated by a letter and a numeral. A lower case letter is used for shafts and a capital letter is used for housings. Numerals indicate the degree of accuracy – the smaller numerals representing closer tolerances than the larger. The letters indicate the location of the shaft and housing limits relative to the inner ring bore and outer ring outside diameter tolerance ranges indicated in Figures 1 and 2 by the symbols KB and hB respectively. Figures 1 and 2 show graphically how the various tolerance classifications result in clearance or interference depending upon how the diameters of the mating parts interact in specific cases.
4. Selection of Shaft and Housing Fits
To select the proper fits, it is necessary to consider the type and extent of the load, bearing type, and certain other design and performance requirements. The required shaft and housing fits are indicated in Tables 1 and 3. The terms “Light”, “Normal” and “Heavy” loads refer to radial loads that are generally related to C r as shown in Figure 3 (C r , being the Basic Dynamic Radial Load Rating computed in accordance with ANSI/ABMA Standards). 4.1 Shaft Fits. Table 1 indicates the initial approach to shaft fit selection. Note that for most normal applications where the shaft rotates and the radial load direction is constant, an interference fit should be used. Also, the heavier the load, the greater is the required interference. For stationary shaft conditions and constant radial load direction, the inner ring may be moderately loose on the shaft. Table 2 shows the shaft diameter deviations and resultant fits for the various tolerance classifications for bore sizes over 3 mm and up to 1250 mm. 4.2 Housing Fits. Table 3 indicates the initial approach to housing fit selection. Note that the use of clearance or interference fits is mainly dependent upon which bearing ring rotates in relation to the radial load. For indeterminate or varying load directions, avoid clearance fits. Clearance fits are preferred in axially split housings to avoid distorting bearing outer rings, The extent of the radial load also influences the choice of fit. Table 4 shows the housing bore deviations and resultant fits for the various tolerance classifications for outer diameter sizes over 10 mm and up to 2500 mm.
5. Design and Installation Considerations
5.1 Effect of Fit on Bearing Internal Clearance. Since interference fitting will reduce bearing radial internal clearance, it is recommended that prospective users consult bearing manufacturers to make certain that the required bearings are correctly specified to satisfy all mounting, environmental and other operating conditions and requirements. This is particularly necessary in those cases where heat sources in associated parts may further diminish bearing clearances in operation. Standard values of radial internal clearances of radial bearings are listed in ANSI/ABMA Standard 20. 5.2 Allowance for Axial Displacement. Consideration should be given to axial displacement of bearing components due to thermal expansion or contraction of associated parts. Displacement may be accommodated either by the internal construction of the bearing or by allowing one of the bearing rings to be axially displaceable. For unusual applications consult bearing manufacturers.