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18_ch 12 Mechanical Design budynas_SM_ch12

# 18_ch 12 Mechanical Design budynas_SM_ch12 -...

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Chapter 12 321 Now we can check the performance at c min , ¯ c , and c max . Of immediate interest is the fom of the median clearance assembly, 9 . 82, as compared to any other satisfactory bearing ensemble. If a nominal 1.875 in bearing is possible, construct another table with t b = 0 and t d = 0 . c b d ¯ T f T max h o P st T max fos fom 0.0020 1.879 1.875 157.2 194.30 × 7.36 0.0030 1.881 1.875 138.6 157.10 8.64 0.0035 1.882 1.875 133.5 147.10 9.05 0.0040 1.883 1.875 130.0 140.10 9.32 0.0050 1.885 1.875 125.7 131.45 9.59 0.0055 1.886 1.875 124.4 128.80 9.63 0.0060 1.887 1.875 123.4 126.80 × 9.64 The range of clearance is 0 . 0030 < c < 0 . 0055 in . That is enough room to fit in our de- sign window. d = 1 . 875 + 0 . 000 0 . 001 in, b = 1 . 881 + 0 . 003 0 . 000 in The ensemble median assembly has fom = − 9 . 31 . We just had room to fit in a design window based upon the ( h o ) min constraint. Further reduction in nominal diameter will preclude any smaller bearings. A table constructed for a d = 1 . 750 in journal will prove this. We choose the nominal 1.875-in bearing ensemble because it has the largest figure of merit. Ans. 12-19 This is the same as Prob. 12-18 but uses design variables of nominal bushing bore b and
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