Draw a labeled sketch of quick return mechanism of shaper and explain its working?
Quick return mechanism
Quick return mechanism : Crank and slotted lever quick return motion mechanism. This quick return mechanism is mostly used in shaping machines, slotting machines and in rotary internal combustion engines. In this quick return mechanism, the link AC (i.e. link 3) forming the turning pair is fixed, as shown in fig. The link 3 corresponds to the connecting rod of a reciprocating steam engine. The driving crank CB revolves with uniform angular speed about the fixed centre C. A sliding block attached to the crank pin at B slides along the slotted bar AP and thus causes AP to oscillate about the pivoted point A. A short link PR transmits the motion from AP to the ram which carries the tool and reciprocates along the line of stroke R1R2. The line of stroke of the ram (i.e. R1R2) is perpendicular to AC produced.
n 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,
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Quick return mechanism Alternate answer :
Links -
1.Slider
2. Crank
3.Frame
4.Slotted Lever
Pairs-
Frame & Slotted lever – turning
Frame & Crank – turning
Crank & Slider – turning
Slider & Slotted lever - Sliding
Construction –
This mechanism is inversion of Single slider crank chain, which is obtained by fixing connecting rod of basic chain.It has three turning pair & one Sliding pair.
Crank is fitted to frame at pt.'A' & slotted lever is fitted to frame at pt.'B'. The crank & slotted lever are connected to each other through slider. The slider is free to slide in side slotted lever. The upper end of slotted lever is attached to the ram of shaping machine through a linkage {The ram and lever connecting to ram are not part of the basic inversion}
Working –
As the crank starts rotating about pt.'A', it also transmits motion to slider. As the slider is fitted inside the slotted lever, the slotted lever starts oscillating about pt.'B'.
As shown in second fig. The forward stroke is making an angle of 
Whereas the return stroke covers and angle of 
From the figure it is clear that angle 
hence forward stroke is takes more time than return stroke . Hence this mechanism is called as quick Return mechanism.
Application –
The mechanism is used in shaping machine.
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