Beam Torque Wrench

The torque wrench was invented in 1918 by Conrad Bahr, a New York City Water Department employee.  The original use was to prevent over tightening of bolts on water main pipes during repairs.  Today, a torque wrench is used where the tightness of bolts and nuts is important. It allows the user to measure the torque applied to the fastener head so it can be tightened to the specifications required. The simplest and most popular form of torque wrench is known as the beam torque wrench.  It consists of a long lever arm between the handle and the wrench head, made of a material which bends elastically in response to applied torque. A second, smaller bar with a mechanical indicator is also connected to the head. When no torque is applied to the lever arm the indicator rests parallel to the lever arm. A calibrated scale is fitted to the handle so that applied torque, and the associated bending of the main lever, causes the scale to move under the indicator. When the desired torque is reached, the user stops applying force.

Beam Torque Wrench

Beam torque wrenches come in many shapes and sizes, with the most popular sizes being 1/4″, 3/8″, and 1/2″.  To learn how to use a beam torque wrench, you can watch the video shown to the right.  Also shown to the right are several popular beam torque wrench models.  You can click on any of the images to read reviews and find out more information about any of the models.  You can also compare prices and features of the torque wrenches shown.

The beam type torque wrench was developed in the late 1920s by Walter P. Chrysler for the Chrysler Corporation and a company known as Micromatic Hone. Paul Allen Sturtevant was licensed by Chrysler to manufacture the torque wrench.

Typical Beam Torque Wrench

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.

An even more sophisticated method of presetting torque is with a calibrated clutch mechanism. At the point where the desired torque is reached, the clutch slips, signaling the desired torque and preventing additional tightening. The most common form uses a ball detent and spring, with the spring preloaded by an adjustable screw thread, calibrated in torque units. The ball detent transmits force until the preset torque is reached, at which point the force exerted by the spring is overcome and the ball “clicks” out of its socket. The advantage of this design is greater precision and a positive action at the set point. A number of variations of this design exist for different applications and different torque ranges. A modification of this design is used in some drills to prevent gouging the heads of screws while tightening them.

With electronic torque wrenches, measurement is by means of a strain gauge attached to the torsion rod. The signal generated is converted by the transducer to the required unit of force (N·m, lbf·ft etc.) and shown on the digital display. A number of different joints (measurement details or limit values) can be stored. These programmed limit values are then permanently displayed during the tightening process by means of LEDs or the display. At the same time, this generation of torque wrenches can store all the measurements made in an internal readings memory. This readings memory can then be easily transferred to a PC via the interface (RS232) or printed straight to a printer. A popular application of this kind of torque wrench is for in-process documentation or quality assurance purposes.  Some information provided by wikipedia.org.

When choosing a beam torque wrench, you will want to know the size and amount of torque you need to apply.  You should also read the manufacturers warranty to know what is covered.  Craftsmen beam torque wrenches are guaranteed forever under their lifetime guarantee on hand tools program, but that may not be the case for the specific model of beam torque wrench you buy.