Mis- -matched involute profiles are recognized as a cause of tooth meshing noise. This paper traces a noise reduction
process applied to a consumer product with anoisy gear set consisting of apowder metal (P/M) pinion driving amolded
plastic gear.
The process started with identifying the objectionable noise frequency components and tracing them to this gear set asa
source. Measurements of profles on both gears showed a mismatch of pressure angles, which could be related to“mean
involute slopes.” When the mismatch was reduced by corrective grinding of test sample pinions, these noise
components dropped to acceptable levels.
Experimental study of the plastic gear shrinkage during molding led to a mold cavity design to achieve the desired
pressure angle. This was accompanied by the introduction of a simple, practical means for molding process control so
that the molded gear“mean involute slope” could be continually matched to that of the P/M pinion. With his in place,
the noise reduction could be maintained, permitting the manufacture and sale of the product.

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