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Unformatted text preview: MECH 325 Machine Elements
Tutorial 2 – Gear Force Analysis 1. Shigley, 9th Ed., Problem 13‐43 (8th Ed., 13‐29). (To be demonstrated by the TA.) The figure shows a 16T 20° straight bevel pinion driving a 32T gear, and the bearing centerlines. Pinion shaft a receives 2.5 hp at 240 rev/min. Assume the gear contact forces occur at the midpoints of the teeth. a. Determine the contact force vector. b. Draw the free body diagram for shaft a including the bearing reactions at A and B. Assume bearing A is to take both radial and thrust loads. 2. Shigley, 9th Ed., Problem 13‐47 (8th Ed., 13‐33). (To be done by the class) A gear train is composed of four helical gears with the three shaft axes in a single plane, as shown in the figure. The gears have a normal pressure angle of 20° and a 30° helix angle. Shaft b is an idler and the transmitted load acting on gear 3 is 500 lbf. The gears on shaft b both have a normal diametral pitch of 7 teeth/in and have 54 and 14 teeth, respectively. Find the forces exerted by gears 3 and 4 on shaft b (don’t worry about determining moments) 3. Adapted from Shigley, 9th Ed., Problem 13‐51 (8th Ed., 13‐37). (To be done by class.) A right‐hand single‐tooth hardened‐steel (not well‐lubricated) worm has a catalogue rating of 2000W at 600 rev/min when meshed with a 48‐tooth cast‐iron gear. The axial pitch of the worm is 25 mm, the normal pressure angle is 14‐½°, the pitch diameter of the worm is 100 mm, and the face widths of the worm and gear are, respectively, 100 mm and 50 mm. The figure shows bearings A and B symmetrically loaded with respect to the worm and 200 mm apart. a. Determine whether A or B should be the thrust bearing (hint: you will learn more about bearings in the next module but for now consider whether you want the bearing in compression or tension) b. Find the force of the worm on the gear c. Draw the free‐body diagram for the worm gear and its shaft ...
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- Fall '10