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Posted by lee on April 24, 2008 at 18:04:04:

I seemed to misplace my equation for the max root radii fillet possible for a specific gear data.
And I am unable to retrieve it from my old HP 42 card reader. This was given to me about 30 years ago.

How ever In reviewing Gear Handbook by Dudley
Chapter 5 pages 5-24, 5-31 & 5-40
5-24
It depicts Eq. 5-33
Root Fillets

rf=0.7[rT+ (ht-a-rT) /(d/2cos2 helix)+ht-(a+rT)]

rf = mim calc fillet radius produced by hobbing or generating grinding
rT = edge radius of generating rack, hob or grinding wheel
ht=whole depth of gear
d= pitch diameter of gear
helix=helix angle (use 0 degrees for spur gears)
then

easiest equation for fillet radius as shown 5-31 & 5-34
reprint from AGMA rf =fillet radius (in basic rack ) coarse pitch
.300/P = rf (20 & 25 deg Pressure Angle)

obsolete system
.157/P= rf (for brown & sharp, AGMA 14.5 deg), & 1.33 x clearance (for full depth AGMA) will add more as time permits

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