Question

A worm gear set is designed to have pressure angle of 30^0 which is equal to the helix angle. The efficiency of the worm gear set at an interface friction of 0.05 is

(a) 87.9%

(b) 77.9%

(c) 67.9%

(d) 57.9%

The question was asked during an online interview.

My question is based upon Standard Spur Gears-1 in section Toothed Gearing & Gear Trains of Machine Kinematics

Answer 1

The correct choice is (a) 87.9%

Explanation: ȵ = tanλ(cosɸ – μtanλ)/cosɸtanλ + μ

tanλ = -μ + √1 + μ^2

tanλ = -(0.05) + √1 + (0.05)^2

tanλ = 0.9512

ȵ = 89.1%

So most suitable option is ‘a’.