Machinery's Handbook, 31st Edition
2470 MOUNTING BEARINGS pieces are often checked on a “Talyrond” or a similar continuous recording instrument ca - pable of measuring to within a few millionths of an inch. Though this may seem extreme, it has been found that shaft deformities will be reflected through inner races shrunk onto them. Similarly, tight-fit outer races pick up significant deviations in housings. In many instrument and in missile guidance applications, such deviations and deformities may have to be limited to less than 0.00002 inch (0.508 m m). In most of these precision applications, bearings are used with rolling elements con trolled to less than 5 millionths of an inch deviation from roundness and within the same range for diameter. Special attention is required both in housing design and in assembly of the bearing to shaft and housing. Housing response to axial excursions forced by bearing wobble (which in itself is a result of out-of-square mounting) has been found to be a major source of small electric and other rotating equipment noise and howl. Stiffer, more massive housings and careful alignment of bearing races can make significant improvements in applications where noise or vibration has been found to be objectionable. Table 22. Commercial Application Alignment Tolerances Feature Location Tolerance Housing Face Runout 1 Square to shaft center within .0004 inch/inch of radius full indicator reading. Outer Race Face Runout 2
Square to shaft center within .0004 inch/inch of radius full indicator reading and complementary to the housing runout (not opposed). Square to shaft center within .0003 inch/inch of radius full indicator reading.
Inner Race Face Runout
3
Cover and Closure Mounting Face Parallelism Housing Mounting Face Parallelism
4 and 5 Parallel within .001.
6
Parallel within .001
4
5
Closure
6
1 2
3
Cover
Squareness and Alignment.— In addition to the limits for roundness and wall variation of the races and their supports, squareness of end faces and shoulders must be closely controlled. Tolerances of .0001 inch (2.54 m m) full indicator reading per inch of diameter are normally required for end faces and shoulders, with appropriately selected limits for fillet eccentricities. The latter must also fall within specified limits for radii tolerances to prevent interference and the resulting cocking of the race. Reference should be made to the bearing dimension tables which list corner radii for typical bearings. Shoulders must also be of a sufficient height to insure proper support for the races, since they are of hard - ened steel and are less capable of absorbing shock loads and abuse. The general subject of squareness and alignment is of primary importance to the life of rolling element bearings.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online