What is quick return mechanism in shaper machine?

Shaper Machine

The whitworth quick return mechanism is shown in below fig 1 and a simple line diagram of the mechanism is shown in below fig 2 . The bull gear is mounted on a large fixed pin A upon which it is free to rotate. The crank plate 4 is pivoted eccentrically upon the fixed pin at 5. Fitted on the face of the bull gear is the crank pin 2 on the top of which is mounted the sliding block 3. Sliding block 3 fits into the slot provided on the crank plate 4. At the other end of the crank plate 4, a connecting rod 6 connects the crank plate by a pin 9 and the ram 8 by a pin 7. When bull gear will rotate a constant speed the crank pin 2 with the sliding block 3 will rotate on a crank circle of radius A2 and the sliding block 3 will cause the crank plate to rotate about the point 5 with a variable angular velocity. Pin 9 fitted on the other end of the crank plate 4 will rotate in a circle and the rotary motion of the pin 9 will be converted into reciprocating movement of the ram similar to the crank and connecting rod mechanism. The axis of reciprocating of the ram passes through the pin 5 and is normal to the line A5

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when the pin 2 is at the position C the ram will be at the extreme backward position but when the pin is at the position B, the extreme forward position of the ram will have reached. When the pin 2 travels from C to B the crank pin 9 passes through the backward position to the forward position in the cutting stroke, and the return stroke is completed when the pin 2 travels from B to C or the the pin 2 to travel through an arc covering CEB is greater than the time taken to move through an arc covering BDC. Thus a quick return motion is obtained by the mechanism. The length of the stroke of the ram may be changed by shifting the position of pin 9 closer or away from the pivot 5, The position of stroke may be altered by shifting the position of Pin 7 on the ram.

Line Diagram of Quick Return Mechanism of Shaper Machine
1. Driving Pinion 2. crank Plate 3. Sliding Block 4. Crank Pin for Connecting Rod 5. Pivot for Crank Plate 6. Ram 7. Bull Gear, A. Fixed Pin
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