Whitworth quick return mechanism

What is whitworth quick return mechanism?

1] Whitworth quick return mechanism is the inversion of a single slider crank chain.

2] Single slider crank chain consists of three turning pairs & one sliding pair.

3] The main aim is to converts rotary motion into reciprocating motion but reversed stroke is quicker in comparison with forwarding stroke.

4] The name states itself that the forward stroke is slower as it is power stroke while return stroke is quick as it is idle stroke.

5] The Whitworth quick return mechanism is generally used in shaper machines & slotting machine in which forward stroke is slower for machining purposes & return stroke is faster as there is no machining process is to be done.

History:

It is invented by British manufacturer Joseph Whitworth in 1840.

Parts and Construction:

Whitworth quick return mechanism is consists of the following components:-

1] Crank:- The crank rotates with uniform angular velocity. It gets power from a pinion wheel or motor.

2] Slotted bar & Slider:- It is a bar with a slot for guiding a slider into it. The slider is connected to the end of the crank. The slotted bar is pivoted at a fixed origin. Its other end is connected to the connecting rod.

3] Connecting rod:- The aim of connecting rod is to converts the rotary motion of the end of the slotted bar into reciprocating motion.

4] Ram:- The ram reciprocates in the horizontal direction. The shaper or slotting tool is mounted onto the ram.

whitworth quick return mechanism

The construction is as follows:-

1) As shown in the above figure, link AC is fixed.

2) Crank AB rotates about origin A with uniform angular velocity.

3) The slider b is mounted at end of crank AB which slides into the slotted bar.

4) Slotted bar is pivoted at C & rotates about point C.

5) At the end of the slotted bar, connecting rod is attached which converts rotary motion to reciprocating motion.

6) The ram is connected at the end of the connecting rod. The ram reciprocates & has a cutting tool mounted on it.

Whitworth quick return mechanism working:

Whitworth quick return mechanism working consists of two strokes:-

1] FORWARD STROKE:-

  • For forward stroke, the crank AB is moves from B2 to B1 in a clockwise direction.
  • At the same time point, X on connecting rod moves from B1 to B2 in a clockwise direction & the ram move in forward direction from Y1 to Y2.
  • [The movement of forward stroke is shown in the figure with a green dotted line]
  • For forward stroke crank AB has to complete angle α.

2] RETURN STROKE:-

  • For return stroke, the crank AB is move from B1 to B2 in a clockwise direction.
  • At the same time, the point X on connecting rod moves from B2 to B1 in a clockwise direction & the ram moves in a reversed direction from Y2 to Y1.
  • For reversed stroke, crank AB has to complete angle β.
  • [The movement of return stroke is shown in the above figure by red dotted line]

Working video by Prithviraj P Shetty:

Relation between time takes for forward & reversed stroke:

1] When the crank moves from B2 to B1 in a clockwise manner, the ram moves from Y1 to Y2 (forward).

It means that, Time for forward stroke of ram = Time to complete angle α by crank

2] When the crank moves from B1 to B2 in a clockwise direction, the ram moves from Y2 to Y1 (return).

It means that, Time for return stroke of ram = Time to complete angle β by crank

3] From the figure as we know β<α. It means that the ram moves quicker in return stroke & it takes much time for forward stroke.

The ratio of time for forward stroke & return stroke is given by,

`\frac{\text{Time for forward stroke}}{\text{Time for return stroke}}` = `\frac{\alpha }{\beta }\ or\ \frac{\alpha }{360-\alpha }`

Whitworth quick return mechanism advantages:

The advantages of the Whitworth quick return mechanism are as follows:-

  1. The idle or return stroke is quicker.
  2. It reduces total machining time.

Whitworth quick return mechanism application:

Whitworth quick return mechanism has the following applications:-

  1. Shaper machine
  2. Slotting machine

FAQs:

  1. What is the difference between Whitworth and quick return mechanism?

    1] In the quick return mechanism the arc of motion of the slotted bar is of the same angle in forward and return stroke, While in the case of Whitworth The arc of forwarding stroke and arc of return stroke is a different angle.
    2] In the quick return mechanism the slotted bar performs reciprocating motion in an arc and in the Whitworth mechanism the slotted bar performs the complete circular motion.

  2. Where is Whitworth quick return mechanism used?

    It is used in shaper machines, slotting machines,s, etc.

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