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November/December 1992

Archive > 1992 > November/December 1992

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Feature Articles

1992 Marks Important Gear Design Milestone: Lewis Bending Strenth Equations Now 100 Years old
Columbus' first voyage to the Americas is not the only anniversary worthy of celebration this year. In 1892, on October 15, Wilfred Lewis gave an address to the Engineer's Club of Philadelphia, whose significance, while not as great as that of Columbus' voyage, had important results for the gearing community. In this address, Lewis first publicly outlined his formula for computing bending stress in gear teeth, a formula still in use today.

Technical Articles

Classification of Types of Gear Tooth Wear - Part I
The phenomena of deterioration of surfaces are generally very complex and depend on numerous conditions which include the operating conditions, the type of load applied, the relative speeds of surfaces in contact, the temperature, lubrication, surfaces hardness and roughness, and the compatibility and nature of materials.

Investigation of the Strength of Gear Teeth
To mechanical engineers, the strength of gear teeth is a question of constant recurrence, and although the problem to be solved is quite elementary in character, probably no other question could be raised upon which such a diversity of opinion exists, and in support of which such an array of rules and authorities might be quoted. In 1879, Mr. John H. Cooper, the author of a well-known work on "Belting," made an examination of the subject and found there were then in existence about forty-eight well-established rules for horsepower and working strength, sanctioned by some twenty-four authorities, and differing from each other in extreme causes of 500%. Since then, a number of new rules have been added, but as no rules have been given which take account of the actual tooth forms in common use, and as no attempt has been made to include in any formula the working stress on the material so that the engineer may see at once upon what assumption a given result is based, I trust I may be pardoned for suggesting that a further investigation is necessary or desirable.

Tooth Contact Shift in Loaded Spiral Bevel Gears
An analytical method is presented to predict the shifts of the contact ellipses on spiral bevel gear teeth under load. The contact ellipse shift is the motion of the point to its location under load. The shifts are due to the elastic motions of the gear and pinion supporting shafts and bearings. The calculations include the elastic deflections of the gear shafts and the deflections of the four shaft bearings. The method assumes that the surface curvature of each tooth is constant near the unloaded pitch point. Results from these calculations will help designers reduce transmission weight without seriously reducing transmission performance.

Departments

The Sum of Our Fears (Publishers Page)
Last month I attended a meeting in Mexico City sponsored by CIATEQ, a quasi-governmental organization in Mexico, which has as one of its aims the encouragement of the growth of the gear industry in Mexico. The purpose of the meeting was to provide a catalyst among the attendees to form a Mexican equivalent of AGMA and to encourage an alliance with AGMA. Joe Franklin, the Executive Director of AGMA, Bill Boggess, the President, Vice-President Ray Haley, and I were among the few Americans at the meeting.

Camshaft Gears (Voices)
One of our readers in England has asked for our help in locating published technical data and information on the design, manufacture, and inspection of camshaft gears. Although millions of these gears have been made and are in constant use, we are not aware of any formal material having been published. We would be pleased to hear from anyone who had knowledge of such information.

Calendar (Events)
Complete calendar for November/December 1992

Management By Walking Around (Management Matters)
Have you ever been confronted by a thorny business problem, only to discover - belatedly - that it has been creeping up on you for months, or even years?