Photoelastic determination of geometry factors for spur gear teeth

Abstract

Geometry factors for spur gear teeth were determined using photoelastic models of 20° full depth involute spur gear teeth. Seven models w ere made representing gears having 20, 25, 30, 40, 60, 80, and 125 teeth respectively, with a diametral pitch of 1/2. The seven models were made in accordance with specifications of the American Gear Manufacturers Association by first machining tem plates of plexiglas to correct dimensions, and then transferring these tooth forms to photoelastic material. The resulting models were mounted in an accommodating straining frame, then placed in a polariscope, and subsequently loaded to simulate the action of a variety of mating gears. More than three hundred photographs were taken of the models under load, and from these pictures stress data were obtained and evaluated after samples of photoelastic material of each model had been calibrated. These stress data were converted to dimension less form, and curves were plotted for comparison with currently accepted values of geometry factors, form factors, and stress concentration factors. Equations were developed from some of the curves. The results of this photoelastic investigation showed very good correlation with currently employed values of geometry factors and some variation in stress concentration factors.