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AGMA 908-B89, Geometry Factors for Determining the Pitting Resistance and Bending Strength of Spur, Helical and Herringbone Gear Teeth AGMA 908-B89, Geometry Factors for Determining the Pitting Resistance and Bending
Strength of Spur, Helical and Herringbone Gear Teeth
In section 5.10 of AGMA 908-B89, we see that the Angle of Inclination of Helical Contact Line
() is defined in equation 5.71 as:
= tan
-1
(tan sin
n
)
(Eq. 5.71)
Where:
= Standard helix angle; n
= Standard normal pressure angle.
This appears to be an error, since in section 6.3.2.3 of AGMA 218.01, we see that the same
variable, named the Load Inclination Angle () is defined in equation 6.59 as:
= tan
-1
(tan sin
n
)
(Eq. 6.59)
Where:
= Helix angle at operating pitch diameter; n
= Normal operating pressure angle.
Question: What is the correct way to calculate the Angle of Inclination of Helical
Contact Line (), using operating or standard angles?
AGMA's response:
The conclusion from the committee is that AGMA 908-B89 is very clear that the angles
should be standard and not operating. The values of J-factors that are tabulated were all
calculated on standard angles. Therefore, the interpretation of AGMA 908-B89 at that time
was to use standard values for the angles.
A further question, although not stated, might be whether the Helical Gear Rating Committee
actually intended for the standard angles to be used. No one is positive, but we believe that
they did for the following reasons:
1. The Wellauer and Siereg paper written in 1960 was the basis of the inclination angle
theory, and it appears to have intended standard angles;
2. AGMA 221.02 (July 1965) was the helical gear rating standard for strength that
existed before AGMA 218. It gives the basic theory for inclination angle and mentions
the generated diameters when addressing formulas associated with these angles;
3. It is true that AGMA 218 used the operating values, but then the AGMA 2001/AGMA
908 combination changed the angles to standard.