Torque Wrench Types
September 14, 2018
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A torque wrench is a specialized tool designed for one purpose. Items held together with bolts or screws stay locked in place by the clamping force created when the male and female threads are pulled tight against each other. When this happens, in order to optimize holding power, there needs to be a balance struck between the stretch of the fastener and its yield point (The point where the bolt or screw becomes permanently elongated). Not enough clamping force and the fastener can come loose. If put under too much force, the screw or bolt can be stretched past its yield point and become weakened, potentially resulting in failure. A torque wrench allows you to accurately tighten a fastener to a predetermined torque value, usually in ft/lbs (foot pounds) or in/lbs (inch pounds). Based of the fastener size and type, this torque value ensures the joint has the maximum holding power while minimizing the potential risk over-tightening. It is important to note that the accuracy of a torque wrench tends to diminish at its extreme upper and lower values. If you find yourself at either end of the scale, it’s best to use a different torque wrench that has your specified value in its midrange.
Below are some of the most commonly available types of torque wrenches:
Beam Style Torque Wrench: Inexpensive and very precise, a beam style torque wrench can be calibrated simply by making sure the indicator is at zero. As torque is applied the beam connecting the handle to the socket flexes, while the indicator rod remains straight. When the beam starts to flex, the pointer at the end of the indicator rod moves along the scale mounted near the handle. When the pointer is at the desired torque value, you are done and the fastener is properly torqued. While they are a simple design, they can be difficult to use in many situations as the dial must be read straight-on to accurately read the torque value.
Spring Loaded Click Style Torque Wrench: One of the most popular styles of torque wrenches, the click style will give slightly, with an audible click when the preset torque value is reached. This is caused by an internal spring and ball detent. As with most torque wrenches, care must be taken as the wrench will continue to apply torque if you keep pushing after the click. These have an advantage over the beam style as you do not have to try and view the scale and indicator while attempting to tighten the fastener. Many times, there is simply not enough clearance to use a beam style torque wrench. A click style torque wrench has a profile much like a traditional ratchet. The torque setting is adjusted by twisting the handle clockwise or counter clockwise and lining up the desired torque setting. Because these wrenches contain a spring, they should always be returned to zero when not in use to maintain their accuracy. Many click style wrenches also have a locking feature on the handle that can be engaged to prevent unintended changes to the torque setting.
Split Beam Click StyleTorque Wrench: While pricier than the spring loaded click style torque wrench, this design eliminates the need of having to zero the tool out after use. There is also no spring to compress and the internal components are at rest no matter what the torque setting it is at. This device works by a wedge that is moved up or down as the torque setting is adjusted. When the beam deflects to the desired torque, it will make contact with the wedge and producing an audible click.
Digital Torque Wrench: More expensive then the beam or click style torque wrenches, the digital torque wrench internally incorporates what is known as a “Strain Gauge”. In the simplest terms a strain gauge is a metallic foil pattern on top of an insulator. When the foil is deformed, the electrical resistance is changed. This gauge is attached to a torsion rod where the electronic signal generated is converted to a torque value and shown on the digital display. These readings can be stored on internal memory and transferred to PC for documentation and quality assurance.