AGMA 231.52 PDF

Introduction 

Measurements over pins on involute spur gears are taken to determine the tooth thickness of a gear-one way, possibly the most accurate way, to determine tooth thickness. There are other methods which use calipers, special micrometers, gear measuring blocks and master gears.

Calipers measure the chordal thickness of gear teeth. Large-flange micrometers are used to determine tooth thickness by measuring over groups of teeth. The number of teeth is so selected that the flanges of the micrometers are tangent to the involutes and their points of contact on a line which is tangent to the base circle of the gear. Gear measuring blocks are, in a way, duplicates of rack teeth. Master gears of known tooth thickness determine gear-tooth thickness by the center distance at which they roll in intimate metal-to-metal contact.

Each one of these various methods of determining the tooth thickness of the gear teeth has its own advantages and .. disadvantages. They have all been known and used for some time. In specific instances, such as for helical, and double helical or herringbone gears, very small or very large gears, large quantity gear production, or the manufacturing of shaper cutters and hobs, one method may be more useful than the others.

In the case of involute spur gears, however, the use of pins has become one of the most popular and accurate methods. Therefore, the following tables and formulas, as well as the standardization of pin diameters are for the purpose of further simplifying and facilitating the use of pins for measuring the tooth thickness of spur gear teeth. The scope of this standard is limited to spur gears coarser than 20 DP. For 20 DP and finer spur gears, see AGMA Standard 207.05, "Tooth Proportions for Fine-Pitch Involute Spur and Helical Gears. "

Dimensions over or between pins can be calculated for any pin diameter. The reason for having standard pin diameters is so that sets of pins for common diametral pitches can be available and standard tables of measuring dimensions can be used. However, to calculate measurements over nonstandard pins, see explanatory information and formulas on pages 6 through 8. In using nonstandard pins, it is preferable that the pins selected will be of a diameter that will permit contact of the pins on the sides of the teeth at about the mean depth and that the pins are large enough to project beyond the tips of the teeth for convenience.

For general explanation of pin measurement of geartooth thickness see AGMA 131.01 Standard Reference Sheet fdr Involute Calculations. Portions of these reference sheets are included in this standard to facilitate the use of nonstandard size wires in emergencies.