Page 391 - Shigley's Mechanical Engineering Design

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366 Mechanical Engineering Design
Figure 7–6

Similar to the arrangement of
Fig. 7–5 except that the outer
bearing rings are preloaded.

Figure 7–7
In this arrangement the inner ring of the left-hand bearing is locked to the shaft between a
nut and a shaft shoulder. The locknut and washer are AFBMA standard. The snap ring in
the outer race is used to positively locate the shaft assembly in the axial direction. Note the
floating right-hand bearing and the grinding runout grooves in the shaft.

Figure 7–8

This arrangement is similar to
Fig. 7–7 in that the left-hand
When components are to be press-fit to the shaft, the shaft should be designed so
bearing positions the entire
that it is not necessary to press the component down a long length of shaft. This may
shaft assembly. In this case
require an extra change in diameter, but it will reduce manufacturing and assembly cost
the inner ring is secured to
by only requiring the close tolerance for a short length.
the shaft using a snap ring.
Consideration should also be given to the necessity of disassembling the compo-
Note the use of a shield to
prevent dirt generated from nents from the shaft. This requires consideration of issues such as accessibility of
within the machine from retaining rings, space for pullers to access bearings, openings in the housing to allow
entering the bearing. pressing the shaft or bearings out, etc.

7–4 Shaft Design for Stress

Critical Locations
It is not necessary to evaluate the stresses in a shaft at every point; a few potentially
critical locations will suffice. Critical locations will usually be on the outer surface, at
axial locations where the bending moment is large, where the torque is present, and
where stress concentrations exist. By direct comparison of various points along the
shaft, a few critical locations can be identified upon which to base the design. An
assessment of typical stress situations will help.