How To Calibrate A Torque Wrench

Is there a good way to calibrate a torque wrench? A torque wrench is a tool that delivers a specific amount of torque to a fastener, such as a bolt, nut, or lag screw. These tools have a wrench shape, but their internal mechanisms vary. Torque wrenches are typically used to ensure the tightening of screws and bolts. Operators can adjust the torque supplied to fasteners according to the application’s standards. The result is that all parts are properly loaded and tensioned. 

A torque wrench indicates bolt tension by measuring torque. The friction between the fastener and the matching hole makes the approach inaccurate because it is not calibrated. Despite being preferred, torque is often the only practical measure available, even if measuring bolt tension (via bolt stretch) is preferred.

It is the same for torque screwdrivers and torque wrenches and they function in the same way. A torque wrench is used by mechanics to apply the proper amount of force to nuts and bolts in cars using accurate and reliable measurements. In contrast, torque wrenches require regular calibration to provide accurate readings. Having your torque wrench calibrated by a professional is preferable, but you can calibrate your wrench at home if you want.

Using a Torque Wrench To Calibrate

1. The length of the square drive from the handle to the square drive

A torque wrench has a square drive to which a socket is attached. In order to keep things simple, use whole inches rather than fractions. Record the distance on paper and mark the point you measured on the handle to remember later.

  • You should put the paper aside until you need it.
  • Using the measurement of 24 inches (61 centimeters), we will proceed to the next step.

2. Hold the square drive in a vice

Bench vices should be oriented so you can insert a square drive torque wrench into them and extend the handle so it is not touching the surface of the table or bench. Once the square drive has been inserted into the vice, tighten it until it is secure.

  • Make sure the torque wrench’s square drive is not damaged by overtightening the vice.
  • In order for the wrench to move under the weight you apply, only the square drive should be caught in the clamp.

3. Calculate your weight to determine the proper setting

Weight divided by handle distance equals handle distance times handle the weight. The torque wrench should be set to the right torque by multiplying the distance measured in step 2 by the weight you intend to use. Inch-pounds equal 40 foot-pounds (480 inch-pounds divided by 12) which is 480 inches times 20 pounds.

  • Start by converting the weight into Newtons if you’re working with metric units. Add 9.807 to the kilogram weight. This example calculates 88.94949 Newtons by multiplying 9.07 kg by 9.807 pounds. To convert Newton meters to Newton’s feet, multiply the number of Newtons times the length in meters: 88.94949 Newton feet x 0.6096 meters = 54.2 Newton’s feet.
  • Newton meters are converted by multiplying by 1.35582. A 40-foot-pound does equal 54.2 Newton meters in this example.
  • The weight and distance figures must be appropriate. Depending on how big your wrench is or what weight you are using, your figures will vary.

4. Hold the weights by the handle of the wrench. 

Making a loop from the rope and the weight allows you to hang it from the torque wrench handle where you marked it in step 1. When you hang the rope, make sure it is short enough so that the weight does not touch the ground.

  • Weigh the wrench, but do not secure it securely. The wrench could be hung instead.
  • The weight needs to hang freely without any obstructions or supports.

How To Calibrate A Torque Wrench

1. Use the torque wrench to adjust the force. 

Torque wrenches usually have a screw midway up the handle where you can adjust the spring tension with a screwdriver. Test the torque wrench by hanging the 20 lb (9.1 kg) weight on your first mark. The weight should fall if the spring is tightened clockwise. If not, lift the weight and lower it again to test.

  • Use the known weight as the torque wrench weight until it clicks once.
  • If the wrench clicks, lift the weight off and then lower it again.

2. Increase the weights if you hear a click.

While hanging your weight from the marked point on the handle, you should hear a click from the torque wrench. To resolve an audible click, lift the weight off the handle and move it up closer to the wrench’s head.

  • The procedure should be repeated until no clicks are heard.
  • Remember to remove the weight each time and put it back down. Don’t slide the weight up the handle.

3. Adjust the weights if you do not hear a click when you lift. 

Place the weight on the torque wrench and listen for a click. If not, move the weight until you hear one.

  • The weight should be moved by an inch or two at a time.
  • Look for the point at which the wrench starts clicking by moving up and down the handle more than one time.

4. Identify the point of transition. 

You need to mark the wrench with a pen where the handle stops clicking once it reaches that point. Identify the exact point by moving the weight up and down the handle several times to determine where it is.

  • The transition point of a handle indicates where it begins to click or stops clicking.

5. Find the transition point from the square drive.

Using the weight as your guide, measure the distance between the square drive and your transition point. Take note of the number and keep it safe. We will use 66 cm (26 inches) for this example, but yours may vary.

  • Ensure that this number is not confused with the figure from step 2.
  • To make sure you have found the transition point correctly, you may want to test finding it more than once.

6. Determine the torque applied.

A torque wrench with a 20-pound transition point at 26 inches, for example, will yield 520 inch-pounds (33.3 foot-pounds) of torque (520 divided by 12 inches).

  • Using the same mains the same: measurement length times weighted by 12. 
  • To convert metric units, multiply the weight in kilograms by 9.807 Newtons, then multiply the result by the length in meters: 9.07 kilograms multiplied by 9.807 Newtons equals 88.95 Newtons. The formula is 88.95 Newton-meters per 0.6604 meters.

7. Identify the difference and correct it.

 When the torque wrench cannot be adjusted, you can still use it fairly accurately by adjusting the settings on the wrench to compensate for the difference. In this case, divide 24 by 26 to get 0.923 (which is 24 divided by 26). In situations in which you must use the torque wrench, multiply this number by the correct torque.

  • To determine the correct torque setting for your torque wrench, multiply your intended torque by the difference.
  • The wrench will still need to be calibrated, but this solution will keep you working.

Calibration Maintenance

1. Reset the scale each time you use it. 

Even though all torque wrenches must be calibrated regularly, and even though you can prolong their life by returning them to zero after every use, you should ensure that you do so.

  • In the absence of zero, it is possible that the calibration will drift due to strain on the internal spring.

2. Ensure that the torque wrench is tightly gripped. 

Your torque wrench’ calibration can be affected by simply dropping it onto a hard surface. You should never use a torque wrench in place of a hammer or lever, so set the torque wrench in safe spots to avoid letting it fall.

  • Its calibration will be affected immediately if you bang it around.
  • It has even been reported that torque wrenches break when dropped.

3. Always use a torque wrench for the right tasks.

 Many people mistakenly use torque wrenches and breaker bars interchangeably due to their similar appearances. They are only intended for use when specific torque requirements exist. Other applications may affect their ability to maintain calibration.

  • The calibration of a torque wrench can be affected or even damaged if it is used instead of a breaker bar or a different type of wrench.
  • Torque wrenches should be treated as specialist tools, not all-purpose tools.

4. Keep your torque wrench’s upper and lower limits in mind. 

Torque wrenches can be damaged if you exceed their limits or may lose their calibration if the limits are exceeded. They come with clear indications of the upper- and lower limits. Make sure you don’t exceed your wrench’s torque rating.

  • A wrench that is torqued beyond its maximum rating may even be damaged.
  • Damage to your torque wrench could render it incapable of holding a calibration.

5. Place the torque wrench by itself in its case. 

You should store your torque wrench in its protective case and separate it from other commonly used tools because torque wrenches can be so easily damaged by impacts and even temperature changes.

  • Ensure that the torque wrench is positioned low to ensure that if it falls, its calibration won’t be significantly damaged.
  • Place the torque wrench somewhere cool and dry. Its calibration may be affected by high or low temperatures or humidity.

Conclusion

With a torque wrench, it’s important to know when you’re going too far. This is why calibration is so crucial. Calibration ensures that your tools are in line with the manufacturer’s settings and allows for more accurate measurements of force applied. Now that you have an understanding on how to calibrate a torque wrench, go ahead and give this post one last read from start to finish! I hope it helps guide you through fixing any problems or questions about using a torque wrench properly. If anything seems unclear after reading, feel free to leave me feedback below so we can work out some kinks before publishing my blog post next week.

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