Problem 3-21 - 3. By virtue of 1 and 2 above, this is a...

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MACHINE DESIGN - An 3-21-1 PROBLEM 3-21 Statement: Figure P3-9 shows an automobile wheel with two common styles of lug wrench being used to tighten the wheel nuts, a single-ended wrench in (a), and a double-ended wrench in (b). In each case two hands are required to provide forces respectively at A and B as shown. The distance between points A and B is 1 ft in both cases. The wheel nuts require a torque of 70 ft-lb. Draw free body diagrams for both wrenches and determine the magnitudes of all forces and moments on each wrench. Is there any difference between the way these two wrenches perform their assigned task? Is one design better than the other? If so, why? Explain. Given: Distance between A and B d AB 1 ft . Tightening torque T 70 ft . lbf . Assumptions: 1. The forces exerted by the user's hands lie in a plane through the wrench that is also parallel to the plane of the wheel. 2. The applied torque is perpendicular to the plane of the forces.
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Unformatted text preview: 3. By virtue of 1 and 2 above, this is a planar problem that can be described in a 2D FBD. Solution: See Figure 3-21 and Mathcad file P0321. F F T 12" = dAB (a) Single-ended Wrench F F T 12" = dAB 6" (b) Double-ended Wrench 1. Summing moments about the left end of the wrench (for either case) T F d AB . 2. Solving for F F T d AB F 70 lbf = 3. This result is the same for both wrenches. Is there any difference between the way these two wrenches perform their assigned task? No, they both require the same two-handed exertion of 70 lb from each hand. Is one design better than the other? If so, why? Explain. FIGURE 3-21 Design (b) has advantages over (a) because it is balanced about the wheel nut. This allows the user to spin the wrench once the nut is loosened. It is also slightly easier to apply the upward and downward forces (F) in a plane with design (b). Free Body Diagrams for Problem 3-21 P 0321.mcd...
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This note was uploaded on 04/26/2010 for the course MAE 3242 taught by Professor N/a during the Spring '10 term at University of Texas-Tyler.

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