Wrench torque vs. Bolt stretch

Thought this to be interesting.

The primary issue semed to be an out of spec torque wrench.

The difference in bolt stretch in that article is the equivalent of torquing one of our head bolts to 22ft.lb instead of 35.
That's a BIG error!
The method of using a torque wrench is simply achieving stretch by assuming the amount of friction the thread surface is experiencing.
Hence the importance of knowing if your desired torque is calculated for dry or wet (oiled).
Every few years I check my 2 torque wrenches against those in a business I know that have theirs calibrated regularly. I haven't yet found an error worth mentioning.

As an aside - in the construction industry where galvanised bolts are used, the torque method is never allowed, because the friction between two galvanised surface is too unpredictable. They use the "part-turn" method instead where the stretch is achieved by turning the nut a calculated amount (after "snug"). Obviously more turns are needed for a longer bolt (or finer thread).

Thanks for posting @MichaelB !
Cheers

I just posted this easy to do torque wrench calibration video on another thread but on topic here as well:



Most commercial wrenches are +/- 3-5% accurate from factory, so the method is good enough for most work.

Tornado said:

I just posted this easy to do torque wrench calibration video on another thread but on topic here as well:



Most commercial wrenches are +/- 3-5% accurate from factory, so the method is good enough for most work.

Click to expand...

Thanks - interesting.
Relies on the luggage scale being in calibration though.

robs ss said:

Thanks - interesting.
Relies on the luggage scale being in calibration though.

Click to expand...

Yes, also the angle you pull at and being able to catch the max reading prior to the click etc etc. But it is easy to repeat four or five times to get an average and will ensure you're in the ballpark. The scale used can also be checked against a known weight.

Got me curious to research how good are typical luggage/fish digital scales. Came across this blurb on a low cost scale which tested out as about 0.1-0.5% accuracy.


Here's the scale tested...less than a ten'r!

Tornado said:

Got me curious to research how good are typical luggage/fish digital scales. Came across this blurb on a low cost scale which tested out as about 0.1-0.5% accuracy.

"Luggage Scale" / Digital Scale - 1 Year Report

In October 2015, we had a discussion titled: Do You Have To Spend Big Bucks For An Accurate Scale? As part of that discussion, board member @Fisher-O-men recommended an inexpensive scale available on eBay (usually advertised as a "luggage scale") as a candidate. Curious, I ordered two of those sc...

www.bassresource.com

Here's the scale tested...less than a ten'r!

Portable Electronic Hanging Fishing Digital Pocket Weight Hook Scale 40kg/10g | eBay

Find many great new & used options and get the best deals for Portable Electronic Hanging Fishing Digital Pocket Weight Hook Scale 40kg/10g at the best online prices at eBay! Free shipping for many products!

www.ebay.com

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I bought one of those a few years ago specifically for torquing the 'usual suspect' barrel/head bolts with an ordinary slim spanner marked at 6"....
Nice to know it's a good 'un