A torque wrench needs calibration to work accurately. When put to use, a torque wrench gradually loses its accuracy. After some time, it needs calibration. As a rule of thumb, you should calibrate snap on torque wrench after around 5000 to 7000 cycles or clicks. Using a torque wrench that is not calibrated is risky. It means that you will easily under-tighten or overtighten components.
There are many methods you can use to calibrate a torque wrench. Some of the techniques require using sophisticated tools. Other ways are simple and only need basic tools. In this article, we will discuss how to calibrate snap on torque wrench in steps.
How to Calibrate Snap on Torque Wrench
You can follow the steps below to calibrate a snap on torque wrench.
Step 1 – Secure the wrench in the vice:
Make sure you firmly clamp the square drive in the vice. You have to be careful not to tie the squared drive together with the head. This way, it won’t be free to turn. The free end of the torque wrench should protrude and hang without problems.
Step 2 – Measure the length of the handle:
Take a measuring tape or meter rule and measure the leverage. Take note of the distance from the centre of the square drive to where you apply the turning force. To make your work easy, stick to whole numbers. For example, if the handle length is 54 cm, take the 50 cm mark.
When using a torque calibration tool, this step is not necessary. Attach the device, and set it in line with the expected torque. In other words, set the torque on the tool according to the torque you have set on the torque wrench.
Step 3 – Mark the application point clearly:
The measurement you took in step two needs to identify where you will hang the weight. You have to make sure that you mark that point with a marker, and it’s visible. You can also skip this step if you are using a tool.
Step 4 – Calculate the weight you intend to use:
If you are using lb-ft, you will take note of the weight in pounds and multiply it by the leverage. But if you use metric units, you must multiply the mass by 9.81. For example, if you used 1 kg for this, you will use 1 x 9.81 = 9.81 N. This is the force you are applying. Then you can also take note of the torque set on the wrench.
Step 5 – Hang the weight on the mark:
When hanging the weight, you have to make sure it has no restrictions. It has to be free to hang.
Step 6 – Calculate the torque output from the weight:
In this case, you move the load until you hear a click. If all is accurate, you will hear the click without making any adjustments. You can then calculate actual torque by multiplying the weight by the distance from the centre of rotation. The length should be in meters.
Step 7 – Compare the torque values and adjust:
The purpose of using calibrated tools is to determine the accuracy and adjust if needed. After noticing the error, you can tune the wrench accordingly.
How accurate are snap on torque wrenches?
Snap on torque wrenches are very accurate. By standard, their accuracy is 3 to 4 %. When supplied with this tool, they also give you a calibration certificate. This way, you are sure that you are being supplied a calibrated torque wrench. When you use this tool for some time, it is only natural to expect it to lose some accuracy over time. That is why calibration essential as it will keep the tool working reliably. Therefore, if you realize that your torque wrench is inaccurate, it could have worked for a long time. But snap on torque wrenches in general, are reliably accurate.
How much does it cost to get a torque wrench recalibrated?
Calibrating a torque wrench does not have a single price. The fees can range from $30 to $200. The price is determined by the type of torque wrench being calibrated. Some of them require more precision than others. While there are also types of torque wrenches that are very expensive. Such wrenches also come with more expensive calibration procedures. The calibrations costs are very reasonable when you consider the cost of using inaccurate wrenches.
So, how to calibrate snap on torque wrench? Make use of the right tools for the calibration process. Sometimes, you can also use other methods that do not need special tools. If you want to use a calibrated tool, there is always a way out. You do not have an excuse for using a wrench that is not calibrated. A calibrated device is the secure way to do quality works.