Torque wrenches are useful devices because they don’t just fasten bolts, they also apply the exact amount of torque force to secure nuts and bolts without causing damage to items these bolts are secured to.
If the calibration on these devices is off, you won’t be able to secure bolts with the light level of tension. This can be a problem for devices that are delicate in design.
It’s important to regularly test the torque range to ensure that it is calibrated correctly. It is also important to get your wrench correctly calibrated if you notice that the readings are off.
In this guide, we are going to show you how to calibrate a torque wrench accurately without the risk of damaging your tool.
What to Do Before Calibrating Your Torque Wrench
Don’t go and fidget with torque wrench calibrations without proper knowledge. It is important to first determine whether calibration is even necessary. There are a few different types of tests that you can conduct to see if the wrench does require calibration.
Of all the testing methods, the easiest one is to use a torque analyzer. This handy device should be able to tell you whether adjustments are needed within a couple of minutes.
How to Calibrate a Torque Wrench
Torque wrenches lose their calibration if they are not handled properly or if the spring inside becomes worn out over time.
Not all torque wrenches should be adjusted at home. Digital torque wrenches, for example, should be taken to professionals for calibration because special tools are required to alter these devices.
Non-digital torque wrenches, however, can be calibrated at home, but the process is a bit complex.
Let’s take a look at the steps for calibrating a torque wrench at home:
Tools You Will Need
- Clicker-style torque wrench
- Marking pen or paint pen
- Tape measure
- Vice that is secured to a bench
- A weight that can be tied with a string
- Rope or a piece of thick string that can handle up to 35 pounds of weight
- A way to record the calculations
- Protective equipment like safety boots
Measure the Wrench Length
First, measure the torque wrench from the head to the handle. Create a marker using the marking pen or paint pen on the handle at an easy-divisible number. For the sake of easy math, we are going to say that the torque wrench we are calibrating is 15 inches.
Get a Reference Weight
Get a weight that can be tied with a string. You can also make a DIY weight with a bottle. To do this, simply grab a bottle, place it on an accurate scale and fill it up to create your weight. For the sake of easy math, we are going to create a weight that weighs 8 pounds.
Calculate Your Reference Weight
You will need to calculate a reference weight so you can calibrate the wrench. To get this weight, you will need to do a little bit of calculation.
The formula Ta = Ts (D1/D2) can be used to calculate the applied torque.
Multiply the length of the wrench (15 inches) by the weight (8 pounds). Next, divide this number (120) by 12 to get 10 foot-pounds. Keep in mind that this is a very low weight-to-torque ratio. In most cases, it is better to work with a larger weight to get the correct setting.
Clamp Down the Wrench
Go ahead and set your torque wrench at 10-foot pounds. Grab a square drive and clamp it into the wrench at a good working level. Alternatively, you can also place a socket on the torque wrench and clamp down a nut in the wrench to which you can connect the socket.
The wrench should hang perfectly level once established. Add the 8-pound weight by hanging it over the edge of the handlebar right where the mark on the handle was created in our first step.
If the wrench is properly calibrated, you should hear a clicking sound if it is set at 10-foot-pound torque settings. If it clicked earlier or later, then you will need to get it recalibrated.
Adjust the Calibration Screw
If your torque wrench is designed with a calibration screw then you can do the calibration yourself. If not, then it might be better to send it to a company that specializes in wrench torque calibration.
To calibrate your wrench, remove the weight from the wrench handle.
If the wrench did not click, then you should tighten up the spring and add the weight again. If it clicks, then your wrench should have a more accurate calibration. If not, then you will need to repeat this step until you do hear that click when the full weight of the weight is added to the handle.
If the wrench clicked before it reached 10 then you will need to loosen up the spring instead of tightening it. Keep loosening it and adding the weight until it clicks when it reaches the proper torque setting.
While calibrating your torque wrench, keep in mind that these devices vary in size. Torque wrenches can be anywhere from 0 – 300 foot-pounds, so larger weights will be required to calibrate larger torque wrenches.
Maintain the New Calibration
Once your torque wrench has been properly calibrated, you should do your best to keep it calibrated. Here are a couple of important steps for keeping your device in good working order:
- Turn the calibration back to zero after each use. Keeping the spring under tension can wear it out much quicker and will affect the torque readings.
- Handle the torque wrench carefully when using it. Bumps or rough handling can affect its calibration.
- Avoid dropping the torque wrench because this is sure to alter its calibration.
- Only use your wrench for appropriate tasks. This tool might look like a breaker bar but should never be used as one.
- Stay within the torque wrenches limitations. This counts for both lower and higher limitations. If you use it for tasks that require more or less force, the calibration can be affected. Do not exceed the maximum torque rating as this could permanently damage your device.
- Store the torque wrench in a secure case all by itself. The case or tool should also be stored in a dry area where it won’t be affected by other elements.
Frequently Asked Questions
What is the length of the torque wrench?
The functional length of a torque wrench is the distance between the center of the square drive of the head of the wrench and the center of the handle. This length can greatly vary because these tools come in many sizes.
Should I consider local gravity during calibration?
In most cases, it is not necessary to keep the local gravity in mind, but some people do like to include it in their calculations so they can calibrate the device more accurately.
We hope this guide taught you how to calibrate a torque wrench, or at least told you which wrenches to take to a specialist for calibration and which ones can be calibrated at home.
If you want to learn even more about torque wrenches or if you are in the market for a quality wrench then take a look at some of our other guides on Nuts and Bolts Fix. With our helpful guides, you can find all the latest and best information on torque wrenches.