Detent
From Wikipedia, the free encyclopedia
Detent is the term for a method and the actual device used to mechanically resist the rotation of a wheel or shaft. It can be used to intentionally divide a rotation into discreet increments, or as in perhaps its original concept and most rudimentary form, to simply arrest rotation in one direction. To arrest movement the method commonly employs a small gravity or spring actuated lever paired with a notched wheel. The lever is mounted on a pivot point in proximity to the wheel so that the end cannot swing completely around and comes into contact with it at a tangental angle less than 90 degrees. The vertical angle of the sides of the notchs 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 so that it 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 notchs 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 attemps to turn in the opposite direction. The lever is jammed in 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 than required to lift or push the lever over the next notch.
Very common examples:
- Any spring powered wind up toy employs one to dissallow the spring to unwind.
- The rachet 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 or nut that it is being employed on in an area where the swing arc of the wrench is limited and to be able to continue to turn it in one direction by simply pulling the handle back and letting the detent reposition itself so the wrench can be forceably turned again.
To resist movement or to create incremental steps methods employed include a spring loaded ball bearing that locates in small incremental depressions, a piece of spring steel that snaps into position on flat surfaces or shallow notches milled into the shaft or wheel.
Common examples:
- A balance control on a piece of stereo 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" ( hence the name ), or volume controls with a separate detent to match each of the digits on the control knob ( typically 10 ).
- Rotary switches typically employ detents to keep the control shaft properly aligned with the appropriate contact.
- Another well known example can be seen on the popular game show Wheel Of Fortune, which employs rubber "fingers" to stop the wheel at valid points on the wheel.
