If you are into mechanical work and professional service then the torque wrench is a useful instrument. It helps you see the right amount of force is applied to the nuts and bolts. In order to use accurate measurements, the wrench will also need to be checked for calibration errors regularly.
- The Three-Part Drill
Before you went on to calibrate the wrench, you must remember that this is to be completed in three parts. And, always respect this tool and use for intended applications only.
- Testing the current calibration.
- Making the correction to the wrench.
- Effectively maintaining this new calibration.
- Check the Current Calibration
Since most torque wrenches are 24 inches or 61 cms long, this measurement can be made using inch tape and a piece of paper. We will record this for further use. This will serve as the marking for hanging weighs baseline for finding the correction factor too.
- Measure the length from the square drive end of the wrench to its handle.
- Mark this point on the handle and note down the inches.
- Use whole numbers and not fractions.
- Put this wrench into a vice such that the square end is inside it while handling towards outside.
- Make sure that the square drive is not overtightened but firmly inside the clamp. Once some weight is given on its handle, the wrench should move while square-end is fixed.
- Get an Appropriate Setting for the Weight Test
Now, decide on a weight you will be using for this. Let us assume that you are using a 20-pound weight. You can even use kilos, 10 kilos let’s say. Multiplying this with 24 inches above tells that 480-pound inch or 200-kilo inch torque is applied.
- The equation always handles the distance times the weight for finding the torque.
- The weight is hanged on the handle of the torque wrench now.
- Just use a rope to hang it completely free, not securely tying it.
- Make Corrections to the Calibration
It is now time to check with the reading and correct the calibration of the wrench. Usually, this can be done by taking a screwdriver and adjusting the spring tension inside the wrench by turning the screw and making it lose or tight.
- Lift up and lower and hang the weight.
- Check to see if the torque wrench clicks at the weight.
- If it doesn’t turn the screw clockwise and tighten the spring, and then do the above two steps once again till it clicks.
- This is a basic method to adjust the tension and calibrate the wrench, but if this method fails, then we have to do this manually as explained below.
- Moving on the Handle for the Click
Now, we shall check to see the distance at which the clicks appear and disappear. This will also give clues that the wrench is calibrated properly. Do note that we had marked at a point on the handle measuring 24 inches. Hang the weight by the rope on this, to begin with.
- Pull up the rope and hang it again to see if the wrench clicks, listen carefully.
- Pull it up again, and rest it bit furthers upwards the handle, and listens for the click.
- Repeat this till you stop listening to the click.
- Move Further Down if the Click Doesn’t Happen
If you placed the weight on the handle at the marked point, but it didn’t click, try the below steps instead. Finding the click is the important part of this step, as much as finding the point where the click stops or begins from no click.
- Move the weight by lifting and resting further down the handle till you can hear the click.
- Start with one inch at a time or lesser.
- When you are trying to find the point of the click, feel free to move both upwards and below the marked point more than once.
- The point where the torque transitions from clicking to no kicking are called “transition point” and are very important. Mark it.
- Record the New Measurements
Once you have found the transition point, which may take several attempts, mark it down on the handle as above, now, we will use our measuring tape and measure from the tip of the wrench, that is, and the square-end till the newly marked point on the handle of it.
- Do not confuse this marking with the one you made in the beginning.
- Maybe use a different color marker for both of them.
- It may require more than one attempt to correctly identify the transition number.
- Calculate the applied torque now using the equation/formula we had mentioned above.
- This time you use the transition point marking and not the initial marking. For example, if the transition was at 25 inches, the torque is 500 pounds-inch or 250 kilos-inch.
- Correct this Change in Calibration Manually
Once you have found this, and if you were not able to adjust the difference by adjusting the tension inside the spring, you can also manually make the corrections using the above measurements.
- You just have to divide the previous measurement with the transition point measure of torque.
- This is called the correct factor.
- Whenever you make a new measurement henceforward, just multiply this correction factor.
- This will give you the correct setting you need for the torque wrench.
- Although you can manually keep using this correction factor to make your measurements and change the settings, the torque wrench still needs to be calibrated somehow.
- Effectively Maintaining this New Calibration
Once the calibration is done, you can do various things to maintain this new calibration. If you were unable to do that using the screwdriver and spring tension, then you have to try something else to get that done. There are methods and simple usage instructions that can avoid the drift in its internal spring and extend the time between the wrench needs re-calibration.
- For time being keep using this correction factor.
- In order to further prolong the lifetime of your torque wrench, you need to keep checking their calibration.
- Every wrench, no matter the quality, will eventually begin to show some slack and get away from the factory calibration.
- Keep in mind to always return the scale to zero every time after you have used the torque wrench.
- Since the maintained force can cause the spring to extend, bringing the scale to zero ensures that it is in neutral condition after use.
- Don’t Drop Them or Abuse Them
Whenever you are using the torque wrench use a firm grip on it. It is unknowingly dropping it on hard surfaces due to poor handling increases the possibility of affecting tool’s calibration. Also, do the same for storing the tool so that it does not fall and effect itself.
- Do not use torque in place of hammer or lever.
- Avoid banging the torque wrench for certain application, even for a short time.
- Using this for a breaker bar or a different type of wrench, apart from its intended application also directly affects its calibration.
- It should always be used for testing the specific torque requirements in your task.
- It is a fragile instrument and does not treat this as an all-purpose mechanical tool like many people.
- When testing for the calibration make sure not to slide your weight but lift it up always and then resting it again on the handle.
- The torque is often also divided by 12 for there are 12 inches to make 30 cms.
- All torque wrenches will need to be calibrated regularly, but using them properly can help to maintain their settings and improve their life.
Some torque wrenches even break when they face a fall or dropped casually.