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Most recent
ANSI/AGMA 1006-A97 (R2023)
Tooth Proportions for Plastic Gears
AGMA has issued standards for gear tooth proportions over a period of many years. The most recent versions have been AGMA 201.02 (withdrawn 1995), Tooth Proportions for Coarse-Pitch Involute Spur Gears, and ANSI/AGMA 1003-G93, Tooth Proportions for Fine-Pitch Involute Spur and Helical Gears. These standards and their predecessors were prepared in response to the need to standardize gear generating cutting tools such as hobs and shaper cutters. Without such standards, the variety of tools needed by gear shops would have become unlimited. The manufacture of gears by the molding process is not subject to the same practical constraints as manufacture by the gear cutting process. Every mold is inherently "non-standard”. The geometry of the mold cavity cannot follow a standard because of varying allowances for shrinkage. Furthermore, there are some methods for manufacturing the mold cavity which do not depend on cutting tools and, even for those that do, special tools are generally required. Thus, tooth proportions for molded plastic gears need not follow those established for machined gears. Some of the special properties of plastic materials influence the selection of gear tooth proportions as the two following examples illustrate: - The structure and orientation of plastic molecules, regardless of processing method, makes the strengths of the materials particularly sensitive to sharp internal corners. A substantially stronger tooth will result if sharp fillets at the base of the tooth are avoided. - - The tooth proportions for gears made according to the AGMA fine-pitch standard noted above generally result in relatively sharp fillets. - In certain applications, the higher expansion properties of plastic materials may create the need for a greater depth of engagement between mating gears than permitted by the other standard tooth forms. As a result of this preference for a different tooth form, members of the plastic gear molding industry have adopted their own individual sets of tooth proportions. One set that has gained wide usage by plastic gear designers, and is often specified in place of the AGMA Fine-Pitch Standard, has been developed by William McKinley [1]. Because these tooth forms contain the preferential features for molded plastic gears and because they are already well recognized in the industry, they were used, with some changes, as models in the preparation of this standard. The first of the four variations in this set has a depth of engagement, or working depth, that is the same as in the above mentioned AGMA standards. The other three have increased depths of engagement in varying degrees. This standard has selected only the first variation, which is the one in widest use, as the model for the new tooth proportions. However, data similarly based on the other three variations are included in annex B. The tooth forms in this standard are defined with the use of the basic rack concept. For those that might be unfamiliar with this concept, a detailed description of the basic rack is included as annex A.
Content Provider
American Gear Manufacturers Association [agma]
