Basic rack

This standard defines a basic rack for spur and helical plastic gears. However, the specific basic rack can be applied to any type of gear which employs the basic rack concept to help define its geometry.

NOTE: This basic rack is an optional alternative to other AGMA basic racks. It will often be preferred for those applications in which tooth bending strength is a major factor in the design of plastic gears.

A detailed description of the basic rack concept, including its features and its application to various types of gears, is given in annex A.

The data for three other basic racks, differing primarily in depth of engagement, are given in annex B.

Gear tooth proportions

This standard shows how basic rack dimensions determine the tooth proportions of the gear once the tooth thickness has been established. Specific values of the gear tooth thickness and the resulting gear tooth proportions are not covered by this standard. However, many of the considerations that go into such a selection are discussed in annex C.

The tip relief from a modified basic rack is discussed in annex D.

Non-traditional practices for defining tooth proportions

Annexes E and F describe some non--traditional practices currently used to help achieve gear designs that are optimum for their applications. Their use with molded plastic gears has been made more convenient by modern methods of mold cavity manufacture. These practices include modifying standard basic racks, creating custom designed basic racks, and designing tooth proportions without reference to basic racks. In the annexes, the description of each method is accompanied by potential advantages and design cautions. An example of one procedure for the last method, designing without reference to basic racks, is presented in annex F.