How to Adjust Torque Wrench Calibration
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The main reason for using a torque wrench is for its accuracy when tightening nuts or bolts. If you don’t know how to use a torque wrench or calibrate it for accuracy, then there is little benefit to using a torque wrench over a conventional wrench.
Calibrating your own torque wrench is an important but unnecessary skill to have. High-quality torque wrenches should already come perfectly calibrated, but even the best torque wrenches will require recalibration eventually after some use.
What is Torque?
Before you attempt to calibrate your torque wrench it is helpful to understand what torque is. Torque is a rotational force, like the force you would use to close a door or swing a baseball bat. Turning any sort of fastener (such as a screw to connect two boards or a lug nut to attach a wheel to a car) uses torque. As they rotate, fasteners compress the objects being attached together. The objects push back against the fastener. This push back causes friction and makes the fastener more difficult to rotate.
Torque wrenches can measure the tightness of the fastener and how much force, or torque, is needed to continue turning a fastener against the increasing friction. Using torque measurement allows you to rotate a fastener to the correct pressure.
Tips for Maximizing the Accuracy of Your Torque Wrench Before You Calibrate It
Check your work
Make sure you have your torque wrench set to the level you want. If you want the dial of your wrench set to 150 but you mistakenly set it at 148 or 152, your work will be inaccurate. Check the scale from multiple angles to ensure you have it at the setting you really want.
Stop at one click
The most commonly used torque wrench is the click torque wrench, named for the noise it makes when it has reached the desired torque level. Other types of torque wrenches have other indicators, such as a beep or popping sound. Be sure to turn your torque wrench slowly and smoothly so as not to exceed just one click. If you turn it past one click, you may have over tightened.
Note the conditions under which your torque is measured. If your nuts and bolts are oily and hot, they may not have the same or as precise of measurements as a clean, cold, and dry bolt. You may be able to match conditions closely enough, but when safety is at stake it is important to be as accurate as possible, such as with working on an automobile, motorcycle, or airplane. Over-torqueing can cause strain and breakage, and under-torqueing can allow parts to fall apart.
Only push the handle
Only use the handle to rotate your torque wrench, not any part of the wrench body. Torque wrenches measure force at the pivot point right underneath the head of the wrench. Torque wrenches are calibrated so that the force matches the amount of torque shown on the display scale when you apply force to the handle, not any other part of the wrench. Forcing any other part of the wrench will give you an inaccurate reading.
How to Calibrate Your Torque Wrench
It’s best to have your torque wrench professionally calibrated or to use equipment specially designed for calibration. However, if you want to calibrate your wrench yourself without professional help, here are the steps to do it.
- Procure a large weight, such as a 50-pound barbell or plate, and a rope. Weigh the weight and the rope together. For this example, let’s say your weight is 50 pounds and your rope is 2 pounds, making the total weight 52 pounds.
- Measure in inches the distance between the middle of your torque wrench’s handle to its drive tang. Divide this number by 12 to get the number of feet. For this example, let’s say the distance from your torque wrench’s handle to drive tang is 24 inches, which divided by 12 is 2 feet.
- Adjust your torque wrench’s settings to the weight of your weight and rope you selected in step one, multiplied by the number of feet you calculated in step two. So for this example, the formula would be 52 pounds x 2 feet = 104 ft.-lbs. of torque.
- Attach the drive end of your torque wrench to something that won’t move so that the wrench is parallel to and level with the ground. You want the ground to be flat, and you can use a level or be sure that the wrench is parallel.
- Tie the rope and weight from step one to the center of your torque wrench’s handle. Make sure not to let the weight touch the ground as this will affect the calibration.
- Check if your torque wrench clicks when it reaches the torque level you calculated in step three. In this example, it should click at 104 ft.-lbs. if it is properly calibrated.