The Principles of Mechanism and Machinery of Transmission; Comprising the Principles of Mechanism, Wheels and Pulleys, Strength and Proportions of Sha (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1882 Excerpt: ... statical pressure on the teeth In addition to statical pressure, however, a different element has to be taken into account, namely, the impacts due to sudden accelerations or retardations of speed. The allowance which must be made to prevent accident from this cause vaiies exceedingly in different kinds of machinery. It is great in the gearing of rolling mills for instance, and in all machinery in which the strains are irregular. Iu calculating the strength of the tooth, it has been usual to consider ft as a short beam fixed at one end, and having the whole of the pressure applied along the extremity of the tooth. But there is a position in which the teeth may be subjected to a severer stress still; owing to the wear of brasses and teeth, we cannot calculate upon the strain bearing always on the whole breadth of the tooth. The pressure may not only come on to the extremity of a tooth, but if any obstruction come in between the teeth, it may be thrown entirely upon one corner of the tooth. In such a case it may be shown, by the rules of maxima and minima, that if E c = c B, the greatest stress will be near the line E B. Tredgold has expressed the strength of a tootb on this supposition by the formula where d is the thickness of the tooth. To allow for wear, however, he adds one-third, so that _fr 5 11.25 In cast-iron /= 15,300, and hence v 1500 Or in words, the thickness necessary for the tooth in inches is equal to the square root of the stress on the tooth in pounds divided by 1500. Hence Tredgold has computed the following table, the breadths of the teeth being deduced, on the principle that the stress should not exceed 400 lbs. per inch breadth: --Table Of Thickness, Breadth, And Pitch Of Teeth O- Wheels. To use this table when the horses' power tra..