==================Part two ============================
5. Hang the weight from the handle where you marked it. (If you have a soft, cushioned grip, protect it with something like a thin piece of rubber.) Here is a picture of what everything should look like.
6. Start adjusting the torque until the handle clicks. If it clicks right away, lift the weights and back off on the setting. Keep going back and forth with the adjustment until you find the setting where it just barely clicks. Every time the wrench clicks you will have to lift your weights to reset it.
7. When you find the transition point between clicking and not clicking, make note of the setting the wrench clicks and write it down.
8. While you are at it, grab a tape measure and measure the distance from the point where the string hangs from the handle to the exact center point of the square drive. If you have a typical wrench with a direction dial on the back, you can usually measure to the midpoint of the dial if it is directly behind the square drive. The more accurate you are with this measurement, the more accurate the results will be. Nearest 1/8” is ok. Convert any fractional measurements to decimal. As an example, 15 5/8” would become 15.63”
9. You will now do this simple calculation; This is a very simple concept. Torque = weight x length. As an example, if you hang 20 lbs exactly one foot from the fulcrum, the torque would be 20 lb.ft. If you went 2 ft. away it would be 40 lb.ft.
Perform the calculation. Multiply the weight of your test weight by the distance you measured and divide by 12 (to convert inches to feet). If you are testing an in.lb. wrench, don’t divide by 12.
The result of your calculation is the actual torque being applied by the weights. Compare it to the setting on the torque wrench and you will have the amount of error. In other words, if your wrench is set to 42 lbs, and the measured torque is 38 lb.ft., the wrench is off by 4 lbs, or 10%. (That’s pretty bad)
An important characteristic of any torque wrench is repeatability. Check the transition point between no click and click numerous times to make sure measurements are repeatable. In this way you can gauge how trustworthy your measurements are. Even the cheapest wrenches should pass this test within 1 lb.ft. or so.
These days, most consumer grade torque wrenches under $75 no longer have a means to align them. If they do, there will be a hole in the handle somewhere with an alignment screw. If there isn’t one, just apply a correction factor into your measurements when adjusting the setting. If the wrench is off by a lot, you are probably better off just getting a new wrench.
I have a 35 year old TRW 1/2" and a 10 year old Craftsman 3/8". Here is what I came up with.
My Test Results: (To give an example)
TRW ½”
37lb x 15.3” = 566.10 /12 = 47.18 lb.ft.
With my TRW and 37 lbs, my calculated torque was 47.18, indicated was 48. I still need to come up with a weight of about 55 lbs to accurately measure the wrench at 80 lb.ft. This is the setting where I normally use it. It is just amazing that a 35 year old wrench that has been dropped numerous times is still this accurate today.
Craftsman 3/8”
12.25 x 21.5 = 263.38 /12 = 21.44 (The wrench was set at 22.5)
12.25 x 37 = 453.25 /12 = 37.77 lb.ft. (The wrench was set at 39)
My inexpensive $75 Craftsman was surprisingly accurate. It was only off by 3% off. That’s pretty darn good for an inexpensive consumer torque wrench.
I hope this helps those that worry about the accuracy of their wrenches.
or
http://www.wikihow.com/Calibrate-a-Torque-Wrench======================================================
I do hope this will help !
