Torque Wrenches

Torque Wrenches

Torque is a force causing torsion (rotation) in a turning device such as a shaft or a threaded bolt.

In the English measuring system, torque is expressed in foot-pounds, inch-ounces, inch-pounds, or (rarely) foot-ounces. In the metric system, torque is expressed in Newton-meters (sometimes stated as Newtons per meter, NpM) or some equivalent, such as Newtons per millimeter.

The exertion of torque (such as that applied to the head of a bolt) may be limited through the use of torque wrenches. This is especially important in softer materials, like aluminum and plastic. In any material, though, undertightening of a bolt can result in it coming loose, and overtightening can result in damaged threads or broken heads. At any rate, torque wrenches come in a variety of styles that may be categorized as either click release torque wrenches or gauged torque wrenches.

A click release torque wrench allows force to be applied up to some limit, set by the operator, then clicks (releases its tension) at the set limit.

A gauged torque wrench is equipped with a meter or gauge which the operator consults to determine the point where tension should be released. The gauge may be a dial or an electronic indicator.

Some split-beam torque wrenches, equipped with a dial (gauge) to indicate how much force is being applied, are also click release, so they fit in both categories.

In the laboratory, torque wrenches are calibrated using force transducers, a sensing device, and some sort of holding fixture to keep the wrench engaged with the transducer while force is being applied and measured.

A transducer is a device which converts one form of energy to another. Many different designs for force transducers are available, most of them having high accuracy and repeatability. J.H. Metrology employs seven different sizes of force transducers to accommodate different ranges of force.

CDI Part Number Socket Size Force Range

2000-8-0 1/4 inch .5 ЁC 400 In.-Oz.

1/4 inch 5 ЁC 50 In.-Lb.

1/4 inch 10 ЁC 100 In-Lb.

3/8 inch 20 ЁC 200 In.-Lb.

2000-8-0 3/8 inch 75 ЁC 750 In.-Lb.

2000-11-0 1/2 inch 25 ЁC 250 Ft.-Lb.

2000-14-0 3/8 & 1 inch 200 ЁC 2000 Ft.-Lb.

The sensing device takes as its input an electrical signal from the force transducer and translates that into an indication of force being applied. J.H. Metrology employs the CDI (Consolidated Devices, Inc.) Computest Force and Torque Tester. The Computest Force and Torque Tester accepts two separate inputs: a 19-pin multiple transducer port and a 10-pin single transducer port.

The holding fixture used by J.H. Metrology is the CDI Low Torque Station Mechanical Loader.

When calibrating a torque wrench, ensure that the Computest is turned off when force transducers are being changed. Secure the transducer in its socket on the mechanical loader using the supplied pins. As previously mentioned, the Computest has two leads for connecting to the selected transducer. Use the 10-pin lead for the three single transducers, and the 19-pin lead for any of the four-ganged smaller transducers.

Turn the Computest on and allow it to warm up for at least thirty minutes before beginning any test. Use the SELECT button to toggle between Torque and Force; select Torque. Use the UNIT button to step through the various measurement ranges (FT-LB, IN-LB, IN-OZ, Nm, dNm, mkg, or cmkg). Use the rotary dial on the upper