Request for Interpretation for AGMA 6123-C16, Design Manual for Enclosed Epicyclic Gear Drives
Issued September 10, 2018
Question:
For identical input, Equation 39 of AGMA 6123-C16, for shear capacity, yields different result compared to similar equation (Equation 4) in Darle Dudleyโs paper โWhen Splines Need Stress Controlโ.
However, if we remove the ฯ from Equation 39, the results are the same.ย See Annex 1.ย
Please review attached sample calculations and explain the difference.
Response from AGMA:
It appears that the original Dudley article referenced by Vanyo has an error in it. Within the โSpline Symbolsโ block, the article states: โtc = chordal thickness at pitch line, in. (approximately equal to D/2N)โ.
I believe that the original intent of the statement was really meant to say that chordal tooth thickness is approximately equal to circular tooth thickness. Since circular tooth thickness equals ฯD/2N, it seems clear that in the printing process, ฯ was inadvertently left off of the equation.
This does not pose a problem to the subsequent article equations since they all just use the symbol tc.
AGMA 6123-B06 and C16 are correct because we chose to use circular tooth thickness for tc and it is calculated correctly with the inclusion of ฯ.
I believe that in general, the gearing industry has recognized this โomission of ฯโ error in the original Dudley article, but I do not have a published reference to this. Perhaps someone else in the committee does.
I looked back in the documentation used by my company (Cincinnati Gearing Systems) to create a spline stress computer program in 1994 and our copy of the Dudley article โWhen Splines Need Stress Controlโ referenced by the questioner has the D/2N equation changed by hand marking to ฯD/2N.