If you need to know for sure whether your torque wrench is calibrated correctly, you can take it to a professional to have it checked.
However, here’s a quick field check you can do yourself on a click type torque wrench: 1)
This is not to be considered a professional calibration. Reason being, there are several factors that can result in errors in testing.
The length measurement can be off depending on how you measure that.
The weight of the wrench can affect the reading.
Bouncing the weight on the handle will change the results.
The weight pulls differently on the handle if the wrench is allowed to turn sideways in the vise before or during the test, changing the results.
There is nothing scientific about the test value or weight used.
If you choose a weight lifting weight marked 20 lbs. Is it really 20 lbs or a little more or less?
If you weigh the subject weight beforehand, are your scales accurate?
If the calculation comes out to a decimal point, how will you set that on the analog scale?
You also have to trust your eyes when setting the torque value on the wrench. This can also be variable depending on your eyes.
All that said, below is the testing procedure.
The test wrench below clicked 5/16” down the handle from the set mark.
The scale would have to be set to 12.518 ft/lbs to deliver 12 ft/lbs of torque to a fastener.
18 lbs weight x 8-5/16“ length (8.3125) = 149.625 in/lbs.
149.625 in/lbs x 0.0835 = 12.494 ft/lbs.
(12.494ft/lbs + .024 ft/lbs subtracted for testing = 12.518 needed to deliver 12 ft/lbs)
So in theory, with the test wrench set to deliver 12 ft/lbs of torque, it would have only delivered 11.482 ft/lbs of torque.
… Or, maybe the fish scale is out of calibration and the wrench is right.
Don't allow wrench travel to touch vise 4) | Make a mark down the handle 5) | Calculate torque value for wrench 6) |
Gently place the weight on the wrench (don't let it bounce). Move the weight up and down handle to find point of click 7) | ||
As a double check, more weight was added to test the wrench at a higher torque value of 22 ft/lbs.
The results were about the same. App 3/8” down the wrench is where it clicked using 34 lbs. and the same 8“ length.8)
In regard to the accuracy of the weight, an in/lb clicker was tested with the 18 lb. steel block.
The wrench was set at 72 in/lbs. with a 4” test length.
The wrench clicked at exactly the end of the mark.
So which wrench is calibrated correctly still remains to be professionally tested but the results are here for your interpretation.
Again, there is nothing scientific about this procedure. But it will get you close using the calibration check above.
If the internal spring has been compromised, the procedure below will not fix the problem.
The spring spreads the load over the entire wrench's torque scale.
So adjusting the tension on the low end will still throw off the torque on the mid to higher end if the spring is no longer functioning properly.
The procedure below is a simple adjustment to correct a situation where the end nut has been allowed to turn and change the tension.
This just helps to change the tension back. Some have used this procedure and seem to like it.
Use the information at your own risk.
On the test wrench, the bushing was turned clockwise originally and the wrench clicked even farther toward the handle end once tested.
Subsequent adjustments and tests with the bushing turned counterclockwise put the test wrench back into calibration (as well as this test will do anyway).
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