The relationship between input torque and tension is the governing principle behind a well-designed bolted joint. Often, calculated values are not reciprocated in field applications. To determine the tension (also known as preload, clamp force, or clamp load), a Skidmore-Wilhelm Bolt Tension Calibrator can be used in association with a known input torque.
Example Test: 3/4″ x 10 Security Locknut
3/4″x10 Security Locknut spun onto bolt
Electric torque gun tightens the locknut onto the bolt
Skidmore-Wilhelm measures bolted joint tension
The friction factor, K, for this particular setup is calculated as 0.17 using the table at the bottom of the page.
This is just one example of when predicted values for bolted joints are not seen in lab testing. A wide variety of outside factors affect torque, tension, and friction. Using a locknut allows for some wiggle room when conditions are not perfect.
Download this torque-tension-friction calculation spreadsheet that is shown above.
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