Shot peening and cryo treating

[Tim Rogers]

Jay, you asked the right question at the right time.  I have been reading
Carrol Smith's book "Engeneer to Win" and last night I read the section on
shot peening.  He has a table that shows the fatigue limit of a piece of E4120
steel tubing being raised from 45,000 psi to 55,000 psi, which is a 22%
increase.
He says about gears:
"The fillets at the tooth roots of gears are areas of extremely high stress
and should be shot peened....  In this case special shot, hardened to Rockwell
C55-C65, should be used.  The tiny indentations produced by the shot don't
hurt anything; in fact there is evidence to suggest that they help by forming
tiny oil reservoirs."
This book is 18 years old, so it does not cover cryo treating, but I'm sure
that you should do that as well given your high HP application.

Tim Rogers