How Often Do Torque Tools Require Calibration?

July 26, 2018
Any company relying on torque tools must have a plan in place to ensure they remain in calibration.

Which force has the biggest effect on our world? Gravity is certainly a strong contender for top dog—it keeps you in your seat, your house on the ground, and the sun in the sky. There is, however, another force that affects our world nearly equally: entropy, gravity’s opposite. If gravity is the tendency things have to come together, entropy is the tendency they have to fall apart. It works to dissolve organization into chaos, reduces large complexities to small simplicities, makes molehills of mountains. It’s the cobwebs in the corners, it’s why your car won’t start, and it’s why the tools you calibrated so carefully are already out of alignment. In short, if you’re creating something complex and precise—for instance, by using electric torque wrenches on an automotive assembly line—it’s not gravity you’re fighting. It’s entropy.

Anyone who uses torque tools regularly is on the front lines of the struggle against entropy. Over time, these tools will eventually end up delivering more or less torque than they are intended to. As a result, the fasteners they’re attaching may end up too loose, allowing them to back off under stress, or too tight, causing them to deform, shear, or otherwise break. Preventing either situation is the reason companies use torque tools in the first place. When tools fall out of calibration, it’s essential to remove them from service until they can be recalibrated to deliver the amount of torque they’re rated for. Even better is to catch entropy in the act by stopping these tools from going out of alignment in the first place. Here’s how.


Calibration Testing Intervals for Torque Tools


One way or another, as you use your torque tools, they will fall out of calibration. Use it and lose it, as the saying goes. That doesn’t mean there’s anything wrong with your tools or even that it’s a bad thing that they go out of calibration from time to time. It’s a natural part of life, a force of nature. The negative outcome, however, is if you use the tools to unknowingly create defective or faulty products. At that point, you may be liable for product failure in the field and will have to deal with the repercussions. So, how do you prevent this from happening? The best way—really, the only way—to be certain your torque tools are in alignment when you use them is to test them, regularly. 


A tool that needs to be tested with each new fastener would be more trouble than it’s worth. On the other hand, if you test your tool only once every few years, then if you find it out of calibration, you’ll have difficulty figuring out how long it has been that way and how many potentially defective products it has created in the meantime.


As a general rule of thumb, it’s wise to test the calibration of your torque tools every six months or twelve months. That’s rare enough that it doesn’t impede productivity and often enough that it doesn’t create obscene liabilities. The organization that owns the tool must determine a suitable calibration frequency that meets their needs based upon many factors, such as history of equipment performance, application, degree of usage, and management objectives. Naturally, tools which show visible signs of wear, such as old grease, worn parts, or loose screws, should be pulled from service and inspected as well. Tools which have been found out of calibration should be flagged and retested at half the normal interval. 

While these general rules are useful as guidelines, your operation’s specific calibration intervals will depend on the precision you need, the exact tools you’re using, the fasteners you’re working with, the criticality of your application, and potentially the legal requirements which govern your industry. To determine an appropriate testing regimen for your operation, consult with the manufacturer, your product’s design team, and other relevant parties, such as your legal team. Certain industries with especially low tolerances for risk may even require a daily torque verification test to ensure no faulty products are assembled.


Testing the Calibration of Your Torque Tools


Fortunately, testing the calibration of your torque tools need not be an onerous or time-consuming procedure. There are two ways to effectively run a testing regimen. Either send your tools to a certified laboratory or test themand document the process yourself. Laboratories should be certified under ANSI/NCSL-Z540, ISO, or N.I.S.T. standards.

Sending tools to a certified laboratory is a preferred solution for companies using small to moderate numbers of torque tools. You must keep an inventory of tools, and workers should remove tools from service at the specified interval. The tools must then be packaged and shipped to the service center, where they will be tested, recalibrated if necessary, repackaged, and shipped back with appropriate documentation. By using a laboratory, companies avoid the the need to invest in and maintain testing and calibration equipment, and of devoting internal resources to testing, calibrating, and documenting the process.


Some operations, however, use so many torque tools or need to test them so regularly that it makes more sense to test their tools in-house. To do so, they rely on torque testers to detect and analyze the output of their tools. When they find tools which are out of alignment, they turn to calibration equipment to return them to proper working order. Testing in-house eliminates the need for packing and shipping tools, which can significantly increase turnaround time. To do so, however, companies must invest in testing equipment and ensure their processes conform to national and international standards.


Any company relying on torque tools must have a plan in place to ensure they remain in calibration. That plan will involve testing their tools at regular intervals, determined by the nature of their work. Testing can be accomplished either by sending tools to a certified laboratory or testing and documenting calibration in-house. However it’s done, it will take regular and consistent attention to keep your tools in alignment and the force of entropy at bay.