ratchet

ratchet
/rach"it/, n.
1. a toothed bar with which a pawl engages.
2. (not in technical use) a pawl or the like used with a ratchet or ratchet wheel.
3. a mechanism consisting of such a bar or wheel with the pawl.
5. a steady progression up or down: the upward ratchet of oil prices.
v.t., v.i.
6. to move by degrees (often fol. by up or down): to ratchet prices up; Interest rates have been ratcheting downward.
[1650-60; alter. of F rochet; MF rocquet a blunt lance-head < Gmc]

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Mechanical device that transmits intermittent motion or permits a shaft to rotate in one direction but not in the opposite one.

Reversible ratchets are used on socket wrench handles and are convenient for tightening or loosening bolts in positions where a complete revolution of a wrench handle is impossible. They are used in mechanical jacks to lock the jack rod after each successive lift.

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▪ mechanical device
 mechanical device that transmits intermittent rotary motion or permits a shaft to rotate in one direction but not in the opposite one. In the Figure—> the arm A and the ratchet wheel B are both pivoted at O. The stem of the pawl P can slide in the arm and is kept in its lowest position by the spring S. If the arm oscillates through the angle α (alpha), the pawl rotates the wheel intermittently in a counterclockwise direction; if the arm rotates clockwise, the sloping side of the pawl rides over the teeth and has no turning effect on the wheel. If the pawl is rotated half a turn so that its sloping side is on the left, oscillation of the arm rotates the wheel in a clockwise direction only. Reversing ratchets of the type described are used on socket wrench handles and are convenient for tightening or loosening bolts in positions where a complete revolution of a wrench handle is impossible. They are also used to obtain an intermittent feeding motion (workpiece movement) on machine-tool worktables; the ratchet wheel is attached to the screw that moves the table, and the arm is driven by a crank, the throw of which can be varied to change α.

 On mechanisms that receive their power from a wound spring, such as watches and clocks, ratchets such as that shown at C in the Figure—> are used. The pawl Q pivots on a fixed axis and rides over the pointed teeth when the spring is being wound but prevents rotation of the wheel in a clockwise direction.

      Although ratchets with pawls and toothed wheels are the most common, other types are used. In one such type, an oscillating member works through a one-way clutch to rotate a wheel intermittently.

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Universalium. 2010.

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