Lead Angle (λ):
The angle at which the teeth are inclined to the normal to the axis of rotation. As illustrate in given figure. Lead angle is the complement of the helix angle,
That means ψ+ λ= 90o
As angle between axes of shafts is 90o
ψ1 + ψ2 = 90o
Or, (90o - λ) + ψ2 = 90o
or, λ= ψ2
That means lead angle of worm = helix angle of work gear
∴ pn of worm = pn of wheel
or, px cos λ= p2 cos ψ2
But
λ= ψ2
∴ px = p2
It refers axial pitch of worm is equivalent to the circular pitch of worm gear.
