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Chapter_8_Solutions - Chapter 8 Note to the Instructor for...

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Chapter 8 Note to the Instructor for Probs. 8-41 to 8-44 . These problems, as well as many others in this chapter are best implemented using a spreadsheet. 8-1 (a) Thread depth= 2 . 5 mm Ans. Width = 2 . 5 mm Ans. d m = 25 - 1 . 25 - 1 . 25 = 22 . 5 mm d r = 25 - 5 = 20 mm l = p = 5 mm Ans. (b) Thread depth = 2.5 mm Ans. Width at pitch line = 2.5 mm Ans. d m = 22 . 5 mm d r = 20 mm l = p = 5 mm Ans. ______________________________________________________________________________ 8-2 From Table 8-1, 1.226 869 0.649 519 1.226 869 0.649 519 0.938 194 2 r m d d p d d p d p d p d d p 2 2 ( 0.938 194 ) . 4 4 t d A d p Ans ______________________________________________________________________________ 8-3 From Eq. ( c ) of Sec. 8-2, tan 1 tan tan 2 2 1 tan R R m m R f P F f P d Fd f T f 0 / (2 ) 1 tan 1 tan tan . / 2 tan tan R m T Fl f f e A T Fd f f ns Chap. 8 Solutions - Rev. A, Page 1/69
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Using f = 0 . 08, form a table and plot the efficiency curve. , deg. e 0 0 0 0.678 20 0.796 30 0.838 40 0.8517 45 0.8519 ______________________________________________________________________________ 8-4 Given F = 5 kN, l = 5 mm, and d m = d p /2 = 25 5/2 = 22.5 mm, the torque required to raise the load is found using Eqs. (8-1) and (8-6)   5 22.5 5 0.09 22.5 5 0.06 45 15.85 N m . 2 22.5 0.09 5 2 R T A ns The torque required to lower the load, from Eqs. (8-2) and (8-6) is   5 22.5 0.09 22.5 5 5 0.06 45 7.83 N m . 2 22.5 0.09 5 2 L T A ns Since T L is positive, the thread is self-locking. From Eq.(8-4) the efficiency is   5 5 0.251 . 2 15.85 e Ans ______________________________________________________________________________ 8-5 Collar (thrust) bearings, at the bottom of the screws, must bear on the collars. The bottom segment of the screws must be in compression. Whereas, tension specimens and their grips must be in tension. Both screws must be of the same-hand threads. ______________________________________________________________________________ 8-6 Screws rotate at an angular rate of 1720 28.67 rev/min 60 n Chap. 8 Solutions - Rev. A, Page 2/69
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