Elementary Lessons with Numerical Examples in Practical Mechanics and Machine Design; With an Introduction by John Perry (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 edition. Excerpt: ...cent. 8. In the case of certain kinds of shafting it is possible to express M as a multiple of T. Thus M = k T. Rankine has found the following values of k: --For such cases as propeller-shafts k varies from-25 to-5. For ordinary light shafting in mills... k -75 to-1. And for crank-shafts and other heavy For each of the cases above mentioned deduce the constant a in the simple formula for the diameter Note.--The values here found agree with values of the multiplier c given at page 99. 9. Find the two equal stresses (tensile and shear) which combined will produce a resultant tensile stress of 66,000 lb. per sq. inch. 10. A cylindric shaft transmits 30 HP at 150 revolutions per minute, and is subjected to a bending moment equal to the twisting moment; find the diameter of the shaft, if the safe shear stress of the material is 9,000 lb. per sq. inch. ANSWEES. 1. Yes. The resultant stress is 5 6 tons per square inch. 2. 6,057-8 lb. per square inch. 3. 6,428 lb. per square inch LESSON XXIV. OVERHUNG CBANK. CRANK-PINS. LENGTHS OP BEARINGS, ETC. A Very good illustration of combined twisting and bending actions is the case of an overhung crank (Fig. 58). Let P be the total push, or pull, of the connectingrod at right angles to the direction of the crank. Fig. 68. Then T = P x A C, and M = P x B C, the resultants of all the forces acting on the journal and crank-pin being assumed to pass through their centres respectively. Then using our rule for combining twisting and bending moments, we have--T( = PxBC + x B C)2 + (P x AC)"2 = PBC + V/b C2 + A C2.-. Te = P (B C + A B). Hence we calculate the twisting moment for an overhung crank as if the crank were of a length equal to the horizontal distance B C, plus the sloping distance A B....