Some folks have much more experience working on cars and motorcycles than I do and they don't even need to use a torque wrench. As a novice mechanic with a strong aversion to screwing up (overscrewing?), I decided that I should check my torque wrench's accuracy. It costs about $25 or so to have this done commercially, but I figured I could make something that would do a reasonably good job of testing the calibration. I decided on making this torque wrench calibrator and I have attached an image of it (it's mostly made of 1-inch square tubing welded together).
Basically you hang a weight (you have to know its weight fairly accurately) on the hook and then crank on the wrench. The thing is designed so that the weight hangs one away foot from the "axle," so if you put 20 lbs on the end, you've got a torque of 20 ft-lbs. Set the wrench to 20 ft-lbs and try it. If it "breaks" lower the setting and try again-keep doing that until it doesn't break. If it does "break" at 20 lbs increase the setting, and try it again. I figure that it's probably accurate to around 10-15%. (There are some frictional considerations, which you could reduce by using bearings, but my wrench clicked at 21to 21.5 ft-lbs and my buddy's wrench about 23 lbs, and this for weight that we measured to be just under 20 lbs on a scale designed for weighing people).You may have noticed that the thing was also designed so that I can use it to balance motorcycle tires, as well.
See a picture of it HERE.
Rich Arimoto
arimoto@cemrc.org
