Torque wrench

A torque wrench is a tool used to apply a specific torque to a fastener such as a nut or bolt. It is usually in the form of a socket wrench with special internal mechanisms. A torque wrench is a tool used to apply a specific torque to a fastener such as a nut or bolt. It is usually in the form of a socket wrench with special internal mechanisms. A torque wrench is used where the tightness of screws and bolts is crucial. It allows the operator to set the torque applied to the fastener so it can be matched to the specifications for a particular application. This permits proper tension and loading of all parts. A torque wrench uses torque as a proxy for bolt tension. The technique suffers from inaccuracy due to inconsistent or uncalibrated friction between the fastener and its mating hole. Measuring bolt tension (indirectly via bolt stretch) is actually what is desired, but often torque is the only practical measurement which can be made. Torque screwdrivers and torque wrenches have similar purposes and mechanisms. The first patent for a torque wrench was filed by John H. Sharp of Chicago in 1931. This wrench was referred to as a torque measuring wrench and would be classified today as an indicating torque wrench. In 1935, Conrad Bahr and George Pfefferle patented an adjustable ratcheting torque wrench. The tool featured audible feedback and restriction of back-ratcheting movement when the desired torque was reached. Bahr, who worked for the New York City Water Department, was frustrated at the inconsistent tightness of flange bolts he found while attending to his work. He claimed to have invented the first torque limiting tool in 1918 to alleviate these problems. Bahr's partner, Pfefferle, was an engineer for S.R. Dresser Manufacturing Co and held several patents. The most basic form of torque wrench consists of two beams. The first is a lever used to apply the torque to the fastener being tightened and serves also as the handle of the tool. When force is applied to the handle it will deflect predictably and proportionally with said force in accordance with Hooke's law. The second beam is only attached at one end to the wrench head and free on its other, this serves as the indicator beam. Both of these beams run parallel to each other when the tool is at rest, with the indicator beam usually on top. The indicator beam's free end is free to travel over a calibrated scale attached to the lever or handle, marked in units of torque. When the wrench is used to apply torque, the lever bends and the indicating beam stays straight. Thus, the end of the indicating beam points to the magnitude of the torque that is currently being applied. This type of wrench is simple, inherently accurate, and inexpensive. The beam type torque wrench was developed in between late 1920s and early 1930s by Walter Percy Chrysler for the Chrysler Corporation and a company known as Micromatic Hone. Paul Allen Sturtevant—a sales representative for the Cedar Rapids Engineering Company at that time—was licensed by Chrysler to manufacture his invention. Sturtevant patented the torque wrench in 1938 and became the first individual to sell torque wrenches. A more sophisticated variation of the beam type torque wrench has a dial gauge indicator on its body that can be configured to give a visual indication, or electrical indication, or both when a preset torque is reached. The dual-signal deflecting beam torque wrench was patented by the Australian Warren and Brown company in 1948. It employs the principle of applying torque to a deflecting beam rather than a coil spring. This is claimed to help prolong the accuracy of the wrench throughout its working life, with a greater safety margin on maximum loading and provides more consistent and accurate readings throughout the range of each wrench. The operator can both hear the signal click and see a visible indicator when the desired torque is reached.