Gear cutting

Abstract

The activity on the project described was divided into three sections: grinding 120 pitch, 12 tooth pinion gears; shaping ratchet wheel teeth; and shaping fine pitch internal gear teeth. These activities were carried to provide new knowledge in the areas of gear cutting. The first activity involved grinding a miniature pinion gear. Bendix had been producing a functional miniature gear by hobbing, but the required surface finish was borderline and burrs on the part were difficult to remove. As a result of this project, a repeatable process was developed for grinding the tooth form and maintaining a 16 ..mu..in. AA (0.41 ..mu..m) surface finish with minimum burrs. The second area investigated was generation shaping ratchet wheel teeth. Because of disadvantages associated with other methods, gear shaping was studied as an alternate, more versatile method of making ratchet teeth. In gear cutting, the reciprocating action of the cutter permits cutting internal teeth and features that are closely banked against obstructions. In addition, irregular, segmented, noncircular, or interrupted configurations can be produced. Initial investigations, using the trial-and-error layout cutter design technique, were found to be too inaccurate for Bendix purposes. Therefore, a mathematical model and computer program were created that will accurately predict whether a desired ratchet tooth geometry can be produced, and will also design the cutting tool. The final activity was shaping internal gear teeth. The test data showed that the standard deviations for the high and low pitch diameters were 0.00036 and 0.00056 inch (9.1 and 14 ..mu..m) respectively and that the total composite error (TCE) had a standard deviation of 0.00051 inch (13 ..mu..m).