Detent
Encyclopedia
Detent is the term for a method, as well as the actual device
Machine
A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, and a molecular machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work...

, used to mechanically
Mechanics
Mechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment....

 resist or arrest the rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

 of a wheel
Wheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

, axle
Axle
An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...

 or spindle
Spindle (tool)
In machine tools, a spindle is a rotating axis of the machine, which often has a shaft at its heart. The shaft itself is called a spindle, but also, in shop-floor practice, the word often is used metonymically to refer to the entire rotary unit, including not only the shaft itself, but its bearings...

.

A detent can be used to intentionally divide
Division (mathematics)
right|thumb|200px|20 \div 4=5In mathematics, especially in elementary arithmetic, division is an arithmetic operation.Specifically, if c times b equals a, written:c \times b = a\,...

 a rotation into discrete increments, or as in perhaps its original concept and most rudimentary form, to simply arrest rotation in one direction.

Arresting movement

To arrest movement, the method commonly employs a small gravity or spring
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

-actuated lever
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

 paired with a notched wheel. The lever is mounted on a pivot point in proximity to the wheel
Wheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

 (so that the end cannot swing completely around) and comes into contact with it at a tangential angle
Tangential angle
In geometry, the tangential angle of a curve in the Cartesian plane, at a specific point, is the angle between the tangent line to the curve at the given point and the x-axis. In geometry, the tangential angle of a curve in the Cartesian plane, at a specific point, is the angle between the tangent...

 less than 90 degrees.

The vertical angle
Vertical (angles)
In geometry, a pair of angles is said to be vertical if the angles are formed from two intersecting lines and the angles are not adjacent. The two angles share a vertex...

 of the sides of the notches that face the direction that rotation is desired is generally acute (45 degrees or less), so that as the wheel rotates in that direction, the end of the lever is easily lifted or pushed out and over the top of a notch. Following this, the lever drops into the next notch and the next et cetera as the wheel or shaft continues to spin.

The angle of the backside of the notch is severe (usually 90 degrees or greater to the end of the lever) so that the lever cannot be pushed up or out of the notch if wheel attempts to turn in the opposite direction. The lever is jammed between the back of the notch and its pivot point, stopping movement in that direction against any force that the materials used can withstand. The wheel has little resistance moving in the direction desired, other than that required to lift or push the lever over the next notch.

Resisting movement

To resist movement (or when creating incremental steps), methods are employed which include a spring-loaded ball bearing
Ball bearing
A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit...

 that locates in small incremental depressions, or a piece of spring steel
Spring steel
Spring steel is a low alloy, medium carbon steel or high carbon steel with a very high yield strength. This allows objects made of spring steel to return to their original shape despite significant bending or twisting.-Grades:...

 that snaps into position on flat surface
Surface
In mathematics, specifically in topology, a surface is a two-dimensional topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3 — for example, the surface of a ball...

s or shallow notches milled
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...

 into the shaft or wheel.

Examples

A well-known example of a detent can be seen on the popular game show
Game show
A game show is a type of radio or television program in which members of the public, television personalities or celebrities, sometimes as part of a team, play a game which involves answering questions or solving puzzles usually for money and/or prizes...

  "Wheel Of Fortune", which employs rubber "fingers" to stop the wheel at valid points after the wheel is spun by a contestant
Contestant
A contestant is someone who takes part in a competition, usually a professional competition or a game show on television. The participants competing against each other have to go through rounds...

. Other common examples include:
  • A balance control on a piece of stereo
    STEREO
    STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...

     equipment which seems to "click" or "snap" into the center position of its rotation, indicating the point where the volumes of the left and right channels are equal or "balanced", or volume controls with a separate detent to match each of the digits on the control knob
    Dial (measurement)
    A dial is generally a flat surface, circular or rectangular, with numbers or similar markings on it, used for displaying the setting or output of a timepiece, radio, clock, watch, or measuring instrument...

     (typically 10).
  • Rotary switch
    Rotary switch
    A rotary switch is a switch operated by rotation. These are often chosen when more than 2 positions are needed, such as a three-speed fan or a CB radio with multiple frequencies of reception or "channels"....

    es typically employ detents to keep the control shaft properly aligned with the appropriate contact.
  • Any spring-powered wind-up toy
    Wind-up toy
    A wind-up toy is a toy powered by a clockwork motor.-History:Wind-up toys date far back into history, into the 15th century. Karel Grod, a German inventor, created some of the first wind-up toys, including a metal fly and a mechanical eagle. Also, in 1509, Leonardo da Vinci created a wind-up lion...

     employs one, in order to disallow unwinding of the spring.
  • The ratchet wrench, which interestingly is employed to intentionally use force against the detent and comes in increasing variety of types. It was designed to allow one to keep the wrench engaged with the bolt
    Screw
    A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

     or nut which it is turning, in an area where the swing arc of the wrench is limited, while being able to continue to turn it in one direction by simply pulling the handle back and letting the detent reposition itself. The repositioning allows the wrench to be forcibly turned again.
  • The scroll wheel
    Scroll wheel
    A scroll wheel is a hard plastic or rubbery disc on a computer mouse that is perpendicular to the mouse surface. It is normally located between the left and right mouse buttons.- Functionality :...

    s on many computer mice, employ detents to divide scrolling into discrete steps.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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