1. Some basic definitions

Reference rack layout

This is a section, normal to the teeth, of a wheel of infinitely large diameter (rack) whose profile is used as the basis for defining a system of cylindrical gears with straight or helical teeth.

The reference line is a straight line in the profile of the reference rack, in relation to which the dimensions of the teeth are defined.

For general-purpose gears with tooth modules within the following limits: 1 < m < 20, figure 1 shows the standardized profile of the reference rack for m = 1. This profile corresponds to involute teeth. It has straight flanks and the following characteristics:

• pressure angle: 20° ;

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