A simple quick return mechanism is shown in the figure.

A simple quick return mechanism is shown in the figure. The forward to return ratio of the quick return mechanism is 2 :1. If the radius of the crank O, P is 125 mm, then the distance d(in mm) between the crank centre to lever pivot centre point should be

	2	=	360 - α
	1		α

or 2α = 360 – α
or α = 120°

∴	α	= 60°
	2

i.e. ∠PO₂ O₁ =30°
In ∆PO₂O₁

tan 30° =	O₁P
	d

⇒ d =	125	= 219.29
	tan 30°

and sin 30° =	125
	x

⇒ x =	125	= 250
	1/2