description
AGMA 908-89, Geometry Factors for Determining the Pitting Resistance and Bending Strength of Spur, Helical and Herringbone Gear Teeth
AGMA 908-B89 (reaffirmed March 2015)

Scope
The procedures in this Information Sheet describe the methods for determining Geometry Factors for Pitting Resistance, I, and Bending Strength, J. These values are then used in conjunction with the rating procedures described in AGMA 2001-B88, Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth, for evaluating various spur and helical gear designs produced using a generating process.

Pitting Resistance Geometry Factor, I
A mathematical procedure is described to determine the Geometry Factor, I, for internal and external gear sets of spur, conventional helical and low axial contact ratio, LACR, helical designs.

Bending Strength Geometry Factor, J
A mathematical procedure is described to determine the Geometry Factor, J, for external gear sets of spur, conventional helical and low axial contact ratio, LACR, helical design. The procedure is valid for generated root fillets, which are produced by both rack and pinion type tools.

Tables
Several tables of precalculated Geometry Factors, I and J, are provided for various combinations of gearsets and tooth forms.

 

Foreword
This Information Sheet, AGMA 908-B89, was prepared to assist designers making preliminary design studies, and to present data that might prove useful for those designers without access to computer programs. The tables for geometry factors contained in this Information Sheet do not cover all tooth forms, pressure angles, and pinion and gear modifications, and are not applicable to all gear designs. However, information is also contained for determining geometry factors for other conditions and applications. It is hoped that sufficient geometry factor data is included to be of help to the majority of gear designers.


Geometry factors for strength were first published in Information Sheet AGMA 225.01, March, 1959, Strength of Spur, Helical, Herringbone and Bevel Gear Teeth. Additional geometry factors were later published in Standards AGMA 220.02, AGMA 221.02, AGMA 222.02, and AGMA 223.01. AGMA Technical Paper 229.07, October, 1963, Spur and Helical Gear Geometry Factors, contained many geometry factors not previously published. Due to the number of requests for this paper, it was decided to publish the data in the form of an Information Sheet which became AGMA 226.01, Geometry Factors for Determining the Strength of Spur, Helical, Herringbone and Bevel Gear Teeth.


AGMA 218.01, AGMA Standard for Rating the Pitting Resistance and Bending Strength of Spur and Helical Involute Gear Teeth, was published with the methods for determining the geometry factors. When AGMA 218.01 was revised as ANSI/AGMA 2001-B88, the calculation procedures for Geometry Factors, I and J, were transferred to this revision of the Geometry Factor Information Sheet. The values of I and J factors obtained using the methods of this Information sheet are the same as those of AGMA 218.01. The calculation procedure for I was simplified, but the end result is mathematically identical. Also, the calculation of J was modified to include shaper cutters and an equation was added for the addendum modification coefficient, x, previously undefined and all too often misunderstood. Appendices have been added to document the historical derivation of both I and J.


Because an analytical method for calculating the Bending Strength Geometry Factor, J, is now available,

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