Book Description

Excerpt from Spur Gearing: Rules and Formulas Internal Spur Gears Design of Spur Gears Gear wheels are such common objects about the machine shop, and are manufactured with such rapidity and ease by the aid of the modern automatic gear cutter, that many seldom stop to think what they really are, why the teeth must be constructed with certain curves, and what it is desired that they shall accomplish. In following chapters we shall take up some of the practical questions, touching upon the calculations that come up in the design, but will here deal chiefly with a few of the theoretical points of the subject that are seldom explained in a simple manner for the benefit of those who have had neither the time nor the opportunity to look into matters of this kind. Suppose there are two wheels arranged as in Fig.1 with their faces in close, frictional contact, and that both are exactly the same size, so Fig.1 that when the crank is turned around once, wheel B will turn exactly once also, provided, of course, there is no slipping between the two wheels. It must be noticed, moreover, that if the crank be turned uniformly, wheel B will not only make the correct number of revolutions relative to A, but it will revolve uniformly, as well; that is, both its total motion and the motion from point to point will be correct. Now there are many places in machine construction where the slipping inseparable from friction wheels cannot be tolerated, and this difficulty might be overcome by fastening small projections to one of the wheels, as on A in Fig.2, and cutting grooves in the other wheel, B. Then, if the crank were turned, wheel B would always make just the right number of turns, even if considerable power were transmitted. It is probable, however, that these projections and grooves would not fulfill the purpose of gear teeth. What is wanted of gear teeth is that they shall give exactly the same kind of motion as corresponding friction wheels, running without slipping. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.