Unformatted text preview: MECH 325 Machine Elements
Tutorial 11 – Shaft Deflections and Review 1. Adapted from Shigley, 9 Ed., Problems 7‐17 and 7‐18 (8th Ed., 7‐7 and 7‐8). The first figure shows a proposed shaft design for Shaft a of the double‐reduction gear train shown in the second figure. A motor connects to the right keyway using a flexible coupling and provides a torque of 2500 lbf∙in at a speed of 1200 rpm. All the gears are spur with 20° pressure angles, Pd = 9 teeth/in and diameters as shown. A ball bearing is planned for the left‐side bearing and a cylindrical roller bearing is planned for the right (the bearing shoulder is 1.75 in). The shaft is machined. All dimensions are in inches. th 24 in 4 in 20 in in Part 1 – To be done by the students a. Draw the shear force, bending moment, and torque diagrams for the shaft Part 2 – To be demonstrated by TA b. Treating the shaft as having a uniform diameter of 1.875 in for all sections between (and including) the bearings, check that the deflection remains within reasonable limits for the left bearing. Use E = 30∙106 psi. Part 3 – To be done by students c. Continuing the analysis from Part b., check that the deflections for the gear (at 9 in) and the right bearing (at 11 in) remain within acceptable limits. d. Determine the minimum fatigue factor of safety by evaluating any critical locations. Use the distortion energy ASME‐Elliptic criterion. Start at the gear set keyway and consider other locations if time permits. (Notes: for 1030 HR steel, Sut = 68 kpsi, Sy = 37.5 ksi, and HB = 137; assume the keyways can be described by the end‐mill keyseat r/d = 0.02 in Table 7‐1, p. 373 (8th Ed. p. 361) e. Determine the factor of safety to first‐cycle yielding f. Determine the bearing life in years assuming 02‐series bearings with 40 mm bore, reliability of 0.9 and commercial gearing. ...
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- Fall '10
- 20°, 1030 HR, 40 mm