Page 485 - Shigley's Mechanical Engineering Design

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460 Mechanical Engineering Design

Bearings Motor

Spur gears Worm

Problem 8–5 [
Bronze
bushings 2 's
C.I.
B Collar
C bearing

2 [ 's
Foot A

8–6 The press shown for Prob. 8–5 has a rated load of 5000 lbf. The twin screws have Acme threads,
a diameter of 2 in, and a pitch of 1 4 in. Coefficients of friction are 0.05 for the threads and
0.08 for the collar bearings. Collar diameters are 3.5 in. The gears have an efficiency of 95 per-
cent and a speed ratio of 60:1. A slip clutch, on the motor shaft, prevents overloading. The full-
load motor speed is 1720 rev/min.
(a) When the motor is turned on, how fast will the press head move?
(b) What should be the horsepower rating of the motor?
8–7 A screw clamp similar to the one shown in the figure has a handle with diameter 3 8 in made
of cold-drawn AISI 1006 steel. The overall length is 4.25 in. The screw is 3 4 in-10 UNC and
is 8 in long, overall. Distance A is 3 in. The clamp will accommodate parts up to 6 in high.
(a) What screw torque will cause the handle to bend permanently?
(b) What clamping force will the answer to part (a) cause if the collar friction is neglected and
if the thread friction is 0.15?
(c) What clamping force will cause the screw to buckle?
(d) Are there any other stresses or possible failures to be checked?

Problem 8–7

A

B