Quick return Mechanism of Shaper .

*Crank and slotted lever quick return motion mechanism*

Or

*Quick return mechanism of shaper machine*

In the extreme positions, AP1 and AP2 are tangential to the circle and the cutting tool is at the end of the stroke.

The forward or cutting stroke occurs when the crank rotates from the position CB1 to CB2 (or through an angle β) in the clockwise direction.

The return stroke occurs when the crank rotates from the position CB2 to CB1 (or through angle α) in the clockwise direction. Since the crank has uniform angular speed, 

Diagram-