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Ratchet (device)

 

 
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In mechanical engineering
Mechanical engineering

Mechanical Engineering is an engineering discipline that involves the application of physics#branches of physics for analysis, design, manufacturing, and maintenance of machine....
, a ratchet is a device that allows linear or rotary motion in only one direction, while preventing motion in the opposite direction. Ratchets are used in many other mechanisms, including clock
Clock

A clock is an instrument used for indicating and maintaining the time and passage thereof. The word clock is derived ultimately from the Celtic languages words clagan and clocca meaning "bell"....
s, capstans
Capstan (nautical)

A capstan is a rotating machine used to apply force to another element, notably used on board ship and on dock walls, for heaving-in or veering ropes, cables, and hawsers....
, turnstile
Turnstile

A turnstile, also called a baffle gate, is a form of gate which allows one person to pass at a time. It can also be made so as to enforce One-way traffic#One-way traffic of people, and in addition, it can restrict passage to people who insert a coin, a ticket, a pass, or similar....
s, spanner
Spanner

Spanner may refer to one of the following.*Spanner, a synonym of wrench*The SpannerTM by AbbeyMoor Medical, Inc. FDA approved prostatic stent for treatment of urethral blockages....
s, winder
Winder

Winder may refer to:* winder , a device for transferring energy into a mechanical storage such as mainsprings or the weights of a longcase clock....
s, cable tie
Cable tie

A cable tie is a type of fastener, especially for binding several electronic cables or wires together, and to organize cables and wires....
s, jacks, screwdriver
Screwdriver

The screwdriver is a device specifically designed to insert and tighten, or to loosen and remove, screws. The screwdriver is made up of a head or tip, which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver....
s, and hoist
Hoist (device)

A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium....
s. The term is also used for a socket wrench
Socket wrench

A socket wrench, more commonly referred to as a ratchet, is a type of wrench, or tightening tool, that uses separate, removable sockets to fit many different sizes of fittings and fasteners, most commonly nut s and Screw#Bolt....
.

hets consist of a gear
Gear

A gear is a component within a Transmission device that transmits rotational force to another gear or device. A gear is different from a pulley in that a gear is a round wheel that has linkages that mesh with other gear teeth, allowing force to be fully transferred without slippage....
wheel or linear rack
Rack and pinion

A rack and pinion is a pair of gears which convert rotational motion into linear motion. The circular pinion engages teeth on a flat bar - the rack....
 with teeth, and a pivoting springloaded finger called a pawl (or in horology
Horology

Horology is the art or science of measuring time. Clocks, watches, clockwork, Sundial, Clepsydra , Timer, Time recorder and marine chronometers are all examples of Measuring instruments used to measure time....
 a click) that engages the teeth.






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In mechanical engineering
Mechanical engineering

Mechanical Engineering is an engineering discipline that involves the application of physics#branches of physics for analysis, design, manufacturing, and maintenance of machine....
, a ratchet is a device that allows linear or rotary motion in only one direction, while preventing motion in the opposite direction. Ratchets are used in many other mechanisms, including clock
Clock

A clock is an instrument used for indicating and maintaining the time and passage thereof. The word clock is derived ultimately from the Celtic languages words clagan and clocca meaning "bell"....
s, capstans
Capstan (nautical)

A capstan is a rotating machine used to apply force to another element, notably used on board ship and on dock walls, for heaving-in or veering ropes, cables, and hawsers....
, turnstile
Turnstile

A turnstile, also called a baffle gate, is a form of gate which allows one person to pass at a time. It can also be made so as to enforce One-way traffic#One-way traffic of people, and in addition, it can restrict passage to people who insert a coin, a ticket, a pass, or similar....
s, spanner
Spanner

Spanner may refer to one of the following.*Spanner, a synonym of wrench*The SpannerTM by AbbeyMoor Medical, Inc. FDA approved prostatic stent for treatment of urethral blockages....
s, winder
Winder

Winder may refer to:* winder , a device for transferring energy into a mechanical storage such as mainsprings or the weights of a longcase clock....
s, cable tie
Cable tie

A cable tie is a type of fastener, especially for binding several electronic cables or wires together, and to organize cables and wires....
s, jacks, screwdriver
Screwdriver

The screwdriver is a device specifically designed to insert and tighten, or to loosen and remove, screws. The screwdriver is made up of a head or tip, which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver....
s, and hoist
Hoist (device)

A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium....
s. The term is also used for a socket wrench
Socket wrench

A socket wrench, more commonly referred to as a ratchet, is a type of wrench, or tightening tool, that uses separate, removable sockets to fit many different sizes of fittings and fasteners, most commonly nut s and Screw#Bolt....
.

Ratchet and pawl

Sperrklinke Schema
Ratchets consist of a gear
Gear

A gear is a component within a Transmission device that transmits rotational force to another gear or device. A gear is different from a pulley in that a gear is a round wheel that has linkages that mesh with other gear teeth, allowing force to be fully transferred without slippage....
wheel or linear rack
Rack and pinion

A rack and pinion is a pair of gears which convert rotational motion into linear motion. The circular pinion engages teeth on a flat bar - the rack....
 with teeth, and a pivoting springloaded finger called a pawl (or in horology
Horology

Horology is the art or science of measuring time. Clocks, watches, clockwork, Sundial, Clepsydra , Timer, Time recorder and marine chronometers are all examples of Measuring instruments used to measure time....
 a click) that engages the teeth. Either the teeth, or the pawl, are slanted at an angle, so that when the teeth are moving in one direction, the pawl slides up and over each tooth in turn, with the spring forcing it back with a 'click' into the depression before the next tooth. When the teeth are moving in the other direction, the angle of the pawl causes it to catch against a tooth and stop further motion in that direction.

Because the ratchet's teeth can only stop 'backward' motion at discrete points, a ratchet does allow a limited amount of 'backward' motion, or backlash
Backlash (engineering)

In mechanical engineering, backlash, sometimes called lash or play, is clearance between mating components, sometimes described as the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established....
, to a maximum of the spacing between its teeth. Where it is desired to eliminate this, a smooth toothless ratchet with a high friction surface like rubber
Rubber

Natural rubber is an elastomer?an Elasticity_ hydrocarbon polymer?that was originally derived from a milky colloidal suspension, or latex , found in the sap of some plants....
 is sometimes used. The pawl bears against this at an angle. Any backward motion causes the pawl to jam against the surface by friction, preventing backward motion with very little backlash.

See also

  • Freewheel
    Freewheel

    In mechanical engineering or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft....
  • Sprag
    Sprag

    A sprag is a one-way freewheel clutch used in a number of applications. It resembles a roller bearing with rollers shaped like a figure eight and cocked with a spring....


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