I Was Wrong About Torque Wrenches
Jan 03, 2014
I was betrayed by my age in a recent blog when I wrote that it's important to apply force to a torque wrench only at the handgrip. Frank from Missouri politely questioned my statement, so I contacted Snap-On Tools' tech support staff and got answers from experts.
In my defense, if you're using an old-school, beam-type torque wrench where you have to read the indicated torque as you apply force to the handle, it DOES matter where you apply force to the handle. The handle on that type of torque wrench literally flexes to produce the torque reading, so you have to apply force to the handgrip to get an accurate reading. That's the type of torque wrench I grew up using, and I incorrectly assumed that modern "click" or "beep" torque wrenches required the same strategy.
I was wrong. It doesn't matter where you apply force to the handle of a click or beep torque wrench---they will click or beep whenever the torque at the wrench's head exceeds the pre-set torque value.
Clicker torque wrenches use a coil spring that applies pressure to the equivalent of a ball bearing sitting in a notch. Setting the torque wrench for, say, 150 ft.lbs cranks the spring against the ball and holds it in place until there is enough force applied to move the ball sideways out of the notch. In an electric "beep" torque wrench, a sensor in the head signals when sideways force exceeds the preset value.
Neither the ball-and-notch or electric sensor "care" where force is applied to the handle--they just signal when torque at the wrench's head exceeds the pre-set value.
So Frank was right---you can grip a click or beep torque wrench anywhere on the handle, and it will accurately signal when pre-set torque is achieved. I truly appreciate his bringing my error to my attention, and enjoyed the opportunity to update my understanding of torque wrenches.
I guess you CAN teach an old dog new tricks. Woof!