Question

The condition of correct gearing is

(a) pitch line velocities of teeth be same

(b) radius of curvature of two profiles be same

(c) common normal to the pitch surface cuts the line of centres at a fixed point

(d) none of the mentioned

This question was posed to me in an interview for internship.

My doubt stems from Toothed Gearing in portion Toothed Gearing & Gear Trains of Machine Kinematics

Answer 1

Right option is (c) common normal to the pitch surface cuts the line of centres at a fixed point

To elaborate: The fundamental condition of correct gearing is the common normal at the point of contact between a pair of teeth must always pass through the pitch point.