Greetings to all. Can someone give me formula to calculate minimum number of teeth to avoid interference in case of helical gears? In one of the book the formula I got gives minimum teeth as 6 with slight undercut permissible. (pressure angle-16.282 degrees & helix angle-36.633 degrees) I am in confusion, whether it is right? Request your reply. Thanks, Rajkumar

Hi Rajkumar , For helical gears, z(min) = 2*cos(beta)/sin^2(alpha) ----(A)-----(Handbook of Mechanical Design,TataMcGraw) beta - helix angle and alpha -pressure angle For practical purposes the limiting number of teeth is taken as 14 (experts opinion) For high speed purposes the limiting number suggested is 18. One can also use the addendum modification factor to be reduce undercutting to a value below the theoretical minimum indicated in above equation (A).Kindly refer Gear Engineering by H.E Muerritt :geek: Regards, DN