A ratchet (occasionally spelled rachet) is a mechanical device that allows continuous linear or rotary motion in only one direction while preventing motion in the opposite direction. Ratchets are widely used in machinery and tools. The word ''ratchet'' is also used informally to refer to a ratcheting

socket wrench A socket wrench (or socket spanner) is a type of spanner (or wrench in North American English) that uses a closed ''socket'' format, rather than a typical open wrench/spanner to turn a fastener, typically in the form of a nut or bolt. The most ...

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Theory of operation

A ratchet consists of a round

gear A gear or gearwheel is a rotating machine part typically used to transmit rotational motion and/or torque by means of a series of teeth that engage with compatible teeth of another gear or other part. The teeth can be integral saliences or ...

or a linear

rack Rack or racks may refer to: Storage, support and transportation * Amp rack, a piece of furniture in which amplifiers are mounted * Autorack or auto carrier, for transporting vehicles in freight trains * Baker's rack, for bread and other bake ...

with teeth, and a pivoting, spring-loaded finger called a ''

pawl A pawl is a movable lever that engages a fixed component to either prevent movement in one direction or restrain it altogether. As such, it is a type of latch and can also be considered a type of dog. It typically consists of a spring-loaded ...

'' (or ''click'', in clocks and watches) that engages the teeth. The teeth are uniform but are usually

asymmetrical Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pre ...

, with each tooth having a moderate slope on one edge and a much steeper slope on the other edge. When the teeth are moving in the unrestricted (i.e. forward) direction, the pawl easily slides up and over the gently sloped edges of the teeth, with a spring forcing it (often with an audible 'click') into the depression between the teeth as it passes the tip of each tooth. When the teeth move in the opposite (backward) direction, however, the pawl will catch against the steeply sloped edge of the first tooth it encounters, thereby locking it against the tooth and preventing any further motion in that direction.

Backlash

Because the ratchet can only stop backward motion at discrete points (i.e., at tooth boundaries), a ratchet does allow a limited amount of backward motion. This backward motion—which is limited to a maximum distance equal to the spacing between the teeth—is called

backlash Backlash may refer to: Literature * '' Backlash: The Undeclared War Against American Women'', a 1991 book by Susan Faludi * ''Backlash'' (Star Wars novel), a 2010 novel by Aaron Allston * Backlash (Marc Slayton), a comic book character from ...

. In cases where backlash must be minimized, a smooth, toothless ratchet with a high friction surface such as

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Types of polyisoprene ...

is sometimes used. The pawl bears against the surface at an angle so that any backward motion will cause the pawl to jam against the surface and thus prevent any further backward motion. Since the backward travel distance is primarily a function of the compressibility of the high friction surface, this mechanism can result in significantly reduced backlash.

Uses

Ratchet mechanisms are used in a wide variety of applications, including these: *

Cable tie A cable tie (also known as a hose tie, panduit, tie wrap, wire tie, zap-straps, or zip tie) is a type of fastener for holding items together, primarily electrical cables and wires. Because of their low cost, ease of use, and binding strength, ca ...

s * Capstans *

Caulking gun Caulk (also known as caulking and calking) is a material used to Seal (mechanical), seal Joint (building), joints or seams against leakage in various structures and piping. The oldest form of caulk consisted of fibrous materials driven into ...

s *

Clock A clock or chronometer is a device that measures and displays time. The clock is one of the oldest Invention, human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, a ...

s *

Computer keyboard A computer keyboard is a built-in or peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or Push-button, keys to act as Mechanical keyboard, mechanical levers or Electronic switching system, electro ...

s *

Freewheel image:Freewheel en.svg, Freewheel mechanism In mechanical engineering, mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission (mechanics), transmission that disengages the driveshaft from the driv ...

(overrunning clutch) *

Grease gun A grease gun is a common workshop and garage tool used for lubrication. The purpose of the grease gun is to apply lubricant through an aperture to a specific point, usually from a grease cartridge to a grease fitting or 'nipple'. The channel ...

s *

Handcuffs Handcuffs are Physical restraint, restraint devices designed to secure an individual's wrists in proximity to each other. They comprise two parts, linked together by a Link chain, chain, a hinge, or rigid bar. Each cuff has a rotating arm whi ...

* Jacks * Anti-rollback devices used in

roller coaster A roller coaster is a type of list of amusement rides, amusement ride employing a form of elevated Railway track, railroad track that carries passengers on a roller coaster train, train through tight turns, steep slopes, and other elements, usua ...

s *

Loom A loom is a device used to weaving, weave cloth and tapestry. The basic purpose of any loom is to hold the Warp (weaving), warp threads under tension (mechanics), tension to facilitate the interweaving of the weft threads. The precise shape of ...

s *

Seatbelt A seat belt, also known as a safety belt or spelled seatbelt, is a vehicle safety device designed to secure the driver or a passenger of a vehicle against harmful movement that may result during a collision or a sudden stop. A seat belt reduce ...

s * Select-fire switch * Slacklines *

Socket wrench A socket wrench (or socket spanner) is a type of spanner (or wrench in North American English) that uses a closed ''socket'' format, rather than a typical open wrench/spanner to turn a fastener, typically in the form of a nut or bolt. The most ...

es *

Tie down straps Tie has two principal meanings: * Tie (draw), a finish to a competition with identical results, particularly sports * Necktie, a long piece of cloth worn around the neck or shoulders Tie or TIE may also refer to: Engineering and technology * T ...

Turnstile A turnstile (also called a gateline, baffle gate, automated gate, turn gate in some regions) is a form of gate which allows one person to pass at a time. A turnstile can be configured to enforce One-way traffic#One-way traffic of people, one-way ...

s *

Typewriter A typewriter is a Machine, mechanical or electromechanical machine for typing characters. Typically, a typewriter has an array of Button (control), keys, and each one causes a different single character to be produced on paper by striking an i ...

Gallery

File:First socket wrench.png, Ratcheting

or spanner. File:Comealong.jpg, A ratchet lever hoist, also known as a 'come-along.' File:ZipTieCrossSection.JPG, The ratchet mechanism of a

cable tie A cable tie (also known as a hose tie, panduit, tie wrap, wire tie, zap-straps, or zip tie) is a type of fastener for holding items together, primarily electrical cables and wires. Because of their low cost, ease of use, and binding strength, ca ...

. File:Turning the bezel on a diving watch to mark a point in time.webm, Setting the bezel of a

diving watch A diving watch, also commonly referred to as a diver's or dive watch, is a watch designed for underwater diving that features, as a minimum, a water resistance greater than , the equivalent of . The typical diver's watch will have a water resis ...

to the start time of a dive. For safety reasons, the ring has a ratchet so it cannot be turned or knocked in the opposite direction.

References

{{Commons category, Ratchets Mechanisms (engineering)

Theory of operation

Backlash

Uses

Gallery

See also

References