Something I came across at work today . . .
Torque, a measure of turning or twisting force, is calculated by multiplying force by distance. For example, if you applied 10 lbs. of force with a 2-ft. wrench, you would get 20 ft.-lbs. of torque; if you applied 20 lbs. of force with a 1-ft. wrench, you would also get 20 ft.-lbs. of torque.
To get the best performance from your torque tool, be sure to hold it by the handle grip and pull slowly and evenly.
Selecting the Correct Torque Range—
For the most accurate performance, the maximum torque you're applying should fall near the middle of the tool's torque range. For example, if you're applying 50 ft.-lbs. of torque, it would be better to choose a wrench with a range of 5 to 100 ft.-lbs., rather than a range of 5 to 50 ft.-lbs.
Accuracy is usually given for 20-100% of a tool's torque range. For example, if the torque range is 20 to 120 in.-lbs., the accuracy statement is true for measurements between 40 and 120 in.-lbs. Below 20% of the torque range, the tool's accuracy often drops off significantly.
Manual Tools vs. Power Tools—
Hand torque tools apply a specific amount of torque and, in some cases, check the amount of torque on a fastener. Power tools, such as impact wrenches and power screwdrivers, usually apply a range of torque on the fastener being tightened and are not intended for applying a specific torque.
Types of Torque Tools—
Electronic tools are the most accurate. Readings can be downloaded into printers, PCs, and dataloggers. Adjustable tools let users set the torque value. Preset tools have the torque set at the factory. Click-style tools signal when torque setting is reached with an audible click that you feel in the grip and a momentary release. Torquing after the signal will cause overtorquing. Torque-limiting tools slip to prevent overtorquing, then won't apply torque again until reset. Flat-beam wrenches are the most accurate nonelectronic torque tools. Round-beam wrenches are the most economical torque tools. Dial tools have a circular scale for monitoring torque as it's being applied.
Certificates of Calibration—
Torque tools are calibrated by the manufacturer and a certificate provides proof of calibration and the date it was completed. Shelf life does not affect the calibration of a torque tool. Common practice is to begin the calibration life at the date of purchase or first use.
The chart below shows how to convert between some of the units used to measure torque. Nm = Newton meters; dNm = deci Newton meters; cNm = centi Newton meters.