Hi everyone,
This is not a new discussion for the car enthusiast. I recently gathered more info on this topic and wanted to share with you.
I’m writing you from Texas where I’m attending a steel conference. Among all the steel suppliers and fabricator booths, I came across a company www.skidmore-wilhelm.com who manufacture testing equipment for fasteners (in fact, this past winter they provided some testing for an F1 team and will be publishing their data in the future – you can read more on their website under “cool projects”).
Skidmore do not believe in torque values for fasteners, as this is not an accurate measure. Turning the nut in a bolted joint creates tension in the bolt. The resulting tension, or stretching of the bolt, creates the clamp force that keeps the joint together. There is no surprise that torque and tension are related primarily by friction. Their tests have shown that 90% of the energy used to tighten a bolt is to overcome friction.
They had one of their calibration machines at the show to demonstrate the correlation between torque and tension in a 3/8” diameter grade 5 bolt. These were new shiny bolts out of a box. Using a digital torque wrench set at 25 Ft-Lbs, the tension on the new bolt was 1800 Lbs.
He then slipped a piece of toilet paper between the nut & bolt and using the same torque wrench at 25 Ft-Lbs, the tension on the bolt increased to 2250 Lbs.
He then lubricated the threads of the bolt using Chapstick (lip balm) and managed to increase the tension in the bolt to 3800 Lbs (that is more than twice the initial torque)!
So if you’re anal like me to torque your bolts properly, release the tension in the torque wrench once you’re done using it (so it will not continue compressing the spring in the wrench and loose accuracy) etc ... all that fine tuning is out the window once the threaded surfaces are lubricated!
D
This is not a new discussion for the car enthusiast. I recently gathered more info on this topic and wanted to share with you.
I’m writing you from Texas where I’m attending a steel conference. Among all the steel suppliers and fabricator booths, I came across a company www.skidmore-wilhelm.com who manufacture testing equipment for fasteners (in fact, this past winter they provided some testing for an F1 team and will be publishing their data in the future – you can read more on their website under “cool projects”).
Skidmore do not believe in torque values for fasteners, as this is not an accurate measure. Turning the nut in a bolted joint creates tension in the bolt. The resulting tension, or stretching of the bolt, creates the clamp force that keeps the joint together. There is no surprise that torque and tension are related primarily by friction. Their tests have shown that 90% of the energy used to tighten a bolt is to overcome friction.
They had one of their calibration machines at the show to demonstrate the correlation between torque and tension in a 3/8” diameter grade 5 bolt. These were new shiny bolts out of a box. Using a digital torque wrench set at 25 Ft-Lbs, the tension on the new bolt was 1800 Lbs.
He then slipped a piece of toilet paper between the nut & bolt and using the same torque wrench at 25 Ft-Lbs, the tension on the bolt increased to 2250 Lbs.
He then lubricated the threads of the bolt using Chapstick (lip balm) and managed to increase the tension in the bolt to 3800 Lbs (that is more than twice the initial torque)!
So if you’re anal like me to torque your bolts properly, release the tension in the torque wrench once you’re done using it (so it will not continue compressing the spring in the wrench and loose accuracy) etc ... all that fine tuning is out the window once the threaded surfaces are lubricated!
D
