The purpose of a torque wrench is to apply the correct amount of torque to a fastener.
But for the tool to provide accurate readings, they need to be calibrated often. Continue reading to understand how to calibrate a torque wrench and why this is necessary.
What Is A Torque Wrench?
Many fasteners, i.e. nuts and bolts, require a specific level of torque according to the manufacturer’s specifications or the machinery’s requirements.
In short, fasteners need to be tightened to the correct tension, particularly on heavy and hazardous machinery where safety is paramount and effective performance is crucial. A tool that can assist with this is a torque wrench.
A torque wrench is a must-have tool for many engineers, mechanics, technicians, plumbers, and agriculturists. It avoids under-tightening or over-tightening fasteners, leading to equipment damage and hazardous situations, which increases the likelihood of injuries.
For example, if lug nuts on a wheel are over-tightened, it can cause premature brake wear, impacting the vehicle's ability to stop when the brakes are applied.
There are various types of torque wrenches available, such as:
To ensure that torque wrenches can accurately measure the tightness of a fastener, they must undergo regular calibration, as mentioned earlier.
This process involves verifying and adjusting the tool's accuracy to meet international standards.
How Often Should A Torque Wrench Be Calibrated?
A torque wrench needs regular calibration because its reliability and accuracy will diminish over time if used often.
How often you should calibrate your torque wrench will depend on certain factors, such as:
1) The frequency at which you use your torque wrench
Using your torque wrench several times a day for various applications will mean calibrating more frequently than if you were only using it weekly.
2) The average load on the torque wrench
Ideally, you should only use around 80% of your torque wrench’s range. Any more than this will require you to have your torque wrench calibrated more often.
3) How to store your torque wrench
If you store your torque wrench for a long time (more than several weeks), ensure that it is on its lowest setting. Otherwise, if kept at a high setting, it can cause the spring to weaken.
4) The environmental conditions
If metal becomes too warm, then it expands. On the other hand, if it becomes too cold, then it contracts. Both these conditions can affect the accuracy of a torque wrench’s reading.
5) After repair
During repairs, torque wrenches are dismantled, so the internal mechanisms are disturbed, which undoubtedly affects the measuring accuracy of the tool.
This is why you must have your torque wrench calibrated after any repairs.
To conclude with this section, the general rule is to calibrate a torque wrench every 5,000 clicks.
Calibrating A Torque Wrench
While a professional can calibrate a torque wrench using torque calibration tools like a torque sensor or torque analyser, you can also perform the calibration yourself.
To do this, you will need a:
- Torque wrench
- Tape measure
- Bench vice
- 20 lb weight
- Safety shoes
- Pen and paper
- Piece of string/rope
1) Take measurements
First, you need to test the calibration of your torque wrench. So, using a tape measure, take the measurement (in whole inches) from the centre of the square drive (where a socket attaches) to the handle.
Mark the point with a pen (or sticker), then write the measurement on paper.
For example, if your torque wrench is 24 inches long (a standard length for torque wrenches), the handle may start 18 inches along the tool.
2) Calculate the appropriate setting
Next, secure the square drive in the bench vice.
Position it so that the wrench handle extends away from the bench. Only the square drive should be locked in the vice, not any other part of the wrench.
To determine the right setting for the torque wrench, you need to:
- Multiply the handle distance (the weight you measured previously) by 20 lb (the weight amount).
Divide the result by 12.
This equation will give you the measurement in foot-pounds (ft-Ibf).
So, using the example measurements from before, this equation would be:
18 (inches) x 20 (lb) = 360
360/12 = 30 (ft-Ibf)
3) Perform a calibration check
Set your torque wrench to 30 (ft-Ibf), which is the result of the equation.
Then, using your string or rope, hang the weight from the marked position on your wrench.
While doing this, the weight should not:
- Touch the ground.
- Slide along the handle. If you need to move the weight, lift it before lowering it to the desired position.
If your torque wrench doesn’t click, readjust the tool.
4) Adjust the torque wrench
You can adjust most torque wrenches by turning a screw, which you usually find within the wrench handle. You will need to turn it towards the right to tighten it.
Apply the weight after you adjust your torque wrench, ensuring it is lifted and replaced to the same position between each adjustment.
Repeat the process until the torque wrench clicks at the setting.
Once the torque wrench clicks, loosen the screw until it no longer clicks. This loosening stage is essential to ensure you didn’t over-adjust before.
Your torque wrench may require repair if you cannot find the transition point (the point at which the wrench starts and stops clicking).
Get in contact with Heamar through the below form if you require your torque wrench to be calibrated.
