There something very similar between a strung-out life and stripped bolts that is nobody wants any of those. Our concern, however, today is limited to the later one. Torque wrenches have made our fastening easier since their very introduction. But using a torque wrench has also brought up the frequent occurrences of snapping or stripping threads and bolts due to excessive force or torque being applied. This tragedy is more likely to occur if you use a torque wrench that is not calibrated correctly. Thus, you have to learn how to calibrate a torque wrench?

So, whenever you find yourself snapping a bolt or two by a torque wrench, it's quite safe to assume that you might not adequately calibrate the torque wrench. Now, the chances are, you find yourself in that hard-spot, and if that’s the case, congratulations! You’ve just come to the right spot. Here we have a detailed walkthrough on how to calibrate a torque wrench so that you don’t have to destroy your precious fasteners anymore.

How to Calibrate a Torque Wrench

Torque wrenches are unique in nature and very different from the regular wrenches we have been using due to their internal torque-setting mechanisms. They are required to maintain the torque-specification as the torque-setting can be changed to suit the torque requirement of various fasteners like nuts and bolts.

A poorly or uncalibrated torque wrench will either be unable to fasten nuts and bolts or end up stripping them. Due to different fasteners having different torque requirements, the torque wrench to be used needs a regular calibration to match those numbers.

Calibrating a torque wrench is a delicate task, and entire calibration process can be divided into two major parts which are –

A. Testing the Calibration and

B. Correcting the Calibration

We have broken these parts down into some straightforward steps below for the ease of application. Follow them with undivided attention, and hopefully, you'll succeed in properly calibrating your torque wrench. There are a few things you'll need to execute the calibration which are –

1. A Load (We’re using one weighing 20 pounds)

2. A rope that can withstand the load’s weight

3. Some pieces of paper for recording

4. A pen or a marker

Now, let get on with the process, shall we?

A. Testing the Calibration

How can you put a thing in its due place without knowing its exact location? The very same principle applied to your torque wrench. To understand how much correction your torque wrench needs, you have to know how much it differs from the required result. To do that, follow these steps carefully –

Step#1. Take measurement from the handle to the square drive

The square drive is very easy to locate. It is at the end of the torque wrench where a socket is attached to. To avoid complexities, use whole inches instead of using fractions. Put a mark on the point you measured to on the handle and then calculate the distance. Record this distance on a piece of paper as you’ll require it later as you advance.

Step#2. Stabilize the square drive in a bench-vice.

Place the square drive of your torque wrench into a correctly oriented bench-vice. Make sure that the handle remains extended out from the bench. Then tighten the bench-vice so that you have stabilized the square drive precisely and locked in the place.

Please, avoid overtightening the bench-vice as it may damage or distort your torque wrench leaving it useless for further usage.

Step#3. Compute the right setting for the applied weight

The correct setting for the torque wrench is crucial. To achieve that, multiply the distance you recorded in step#1 say 24 inches by the weight you are going to apply to say 20 pounds. That rounds up to 480-inch pounds or 40-foot (12.2 m) pounds.

Always make sure that you’re using the correct distance, and the exact weight as different size and different weights applied will result in variant outcomes.

However, no matter the size or the weight applied, the equation will still be the same. That is, (handle distance x applied weight/ 12).

Step#4. Apply the weights to the handle of the wrench.

Apply the weight to the wrench-handle by hanging it from the handle by a rope. Make sure that the rope is capable of handling the load. Tie one end of the rope to the weight and the other to the point you marked in step#1.

B. Correcting the Calibration

Now you have already tested the calibration of your torque wrench, the next steps call for amending the calibration. In order to do that, follow these easy steps –

Step#1. Use the weight to adjust the torque wrench

You can easily adjust the spring tension in a torque wrench by twisting a screw located on the wrench-handle. You can do this by using a screwdriver or a similar tool to complete the process.

Apply the weight by hanging the weight from your torque wrench at the place you had marked before. Wait and listen carefully for a click sound if your torque wrench has a click on a limit feature like most other modern torque wrenches. If no click sound is heard or felt, twist the screw clockwise to tighten the spring. Carefully lift the weight off the wrench and then lower it again each time to test for the click sound.

Repeat the same process continually until you hear your torque wrench make the click sound. Don’t tighten the spring after the click sound has been heard or felt.

Step#2. Relocate the weights up the handle on hearing a click sound

Modern torque wrenches have a click on a limit feature that makes a click sound when the preset torque limit is reached. On hearing the sound, remove the weight off the handle and again, hang it down from an upper portion of the wrench's handle toward the head of the wrench.

Repeat the same steps until you no longer hear the click sound. That would mean that the preset torque limit doesn't exceed, and we can go further with the next steps.

Step#3. Move the weights upon not hearing any click

When you do not hear any click coming from the torque wrench, move the applied load further down the wrench-handle. If you’re not sure about how much distance to move the weight, you can simply move by an inch or so. That’ll do the trick.

Keep moving the weight until you start hearing the click sound and stop immediately upon hearing or feeling it.

Step#4. Locate the transition point

After you start hearing the click sound again, take a marker and mark the new transition point where the weight is presently applied. Move the weight up and down, again and again, to make sure that you have identified the point of transition. It's crucial to identify the point adequately as otherwise, it will result in errors and terms, improper calibration.

Step#5. Find out the distance from the square drive to the point of transition

Compute the distance from the square drive to the point of transition using a measuring tape. Track the number on a piece of paper as you’ll need it soon. Let’s just assume that, the distance you measured is 26 inches.

However, the distance you measured can be very different, and that's completely okay. No matter the distance, the calculating procedure is just the same.

Step#6. Find out the applied torque

Now we have to use the torque equation, which is, (handle distance x applied weight/ 12).

In our example, we have chosen the transition point at a distance of 26 inches with a 20 pounds load hung on it. Now multiplying the distance by 20 pounds, we can determine the amount of applied torque which is 520-inch pounds. Dividing by 12 inches, we get 50-foot pounds.

Step#7. Correct for the difference you identify

If you are facing complexities with adjusting the torque wrench, there is another way to use it quite accurately. In this case, you need to compensate for the difference by adjusting the torque setting.

Take up the paper where you recorded your first measurement. In our example, we took it as 24 inches. Now divide that by the distance of point of transition which, in our case, is 24 inches. Doing so will result in 0.923 approximately.

Now you can use this number usefully by multiplying it by the correct torque when you use your torque wrench.

Doing so will give you the appropriate torque- setting for your specific kind of torque wrench. However, keep that in mind that your torque wrench will still need to be calibrated.

Final Thoughts

From snapped bolts to stripped threads – tragedies like these have bothered the motorheads for a long time now. However, this is also a good reminder of why you should always pay due respect to the required torque specifications where maintaining them is a must. Therefore, the necessity of calibrating your torque wrench regularly and adequately before application has an importance that can't be described in mere words.  So, you have learnt how to calibrate a torque wrench yourself for getting proper torque.