Do extensions effect torque measurements?

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gar said:
I think that with a click type torque wrench and a long extension shaft that it is quite possible to produce a greater torque at a fastener than that of the click point torque. We have stored energy in that long shaft at the time of breakaway in the wrench. Where does that energy go and how fast? I don't have such a wrench to try.
Click to expand...

Not if you use the wrench correctly and go slow and steady and use the proper sized extensions. I could see a problem using a 1/2" wrench set at 100 ft lbs with a 1/4" extension. But a 1/4" torque wrench won't twist a 1/4" extension.

I worked in the automotive field for years. They are very picky about torque settings, especially on head bolts and cast aluminum wheel lugs. They have different specs for dry and lubed bolts, but none related to using an extension or lack thereof. If it made so much as a 1% difference, we would have learned about that in school. Some of our classes were at the old Chrysler Tech Center in Highland Park. (12000 Chrysler Drive)
 
171105-2402 EDT

My following discussion probably has little relevance to an ordinary electrician and their needs but it may be useful background.

I obtained a Craftsman adjustable click type wrench today. This one has a minimum setting of 25 #-in, about 2 #-ft. Physically this wrench is too heavy for working at 25 #-in. I used the 100 #-in as more realistic for the test. Craftsman specifies the wrench as +/-4% accuracy.

The initial test was direct coupling to a 600 #-in torque transducer via a square to square socket. This means the input to the socket was a 3/8" square drive from the 3/8" torque wrench, and that socket could drive a 1/2" square shaft. Happen to have a 1/2" square driver on the torque transducer.

Seldom could I prevent overshoot after the breakover point. Thus, even though the breakover point was relatively consistent there would be an impact oscillation after the breakover. This could be rather large, but not consistent.

Adding a standard 3/8" x 12" extension I could not prevent the overshoot. I don't know what one of the so called "torque limiting extension"s would do. Most seem to be up in the 100 #-ft range.

Is the overshoot important? Probably not because the available energy may not do much.

A test on a softer joint would be more informative.

A 10-32 screw would possibly require about 20 to 30 #-in. See https://www.engineersedge.com/torque_table_sae.htm as one source.

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post #43

the overshoot is from what ? its not in the break-over area where this occurs. its likely the force still in your arm on the wrench as you pass past the break-over area. a better wrench might have a bigger break-over area so you have enough time to remove force from the wrench. or, if its critical, a computerized wrench is needed.

eg; a ball ended rope, you and pal each pull it towards you with great force (net zero, no movement) but friend releases "instantaneously" and you knock yourself in the nose ;)
 
171106-2353 EST

The answer to the title of this thread is yes.

Tonight I created an extension 20" long, quite makeshift, but sufficiently good results to provide the above yes answer.

The extension consisted of a 20" long piece of 1/2" square aluminum tubing with a wall thickness of about 1/16". Unknown alloy, but probably mechanically similar to 6061. The modulus of elasticity of aluminum is about 1/3 that of steel, and may have a better damping factor.

Test was run with sockets that would slip over the tube.

Over a number of trials with the Craftsman click wrench I had no appreciable torque overshoot, and I made no effort to very slowly approach the click point. However, I did not go fast. I took several seconds to reach click. No effort to go very slow near click.

.
 
gar said:
171106-2353 EST

The answer to the title of this thread is yes.

Tonight I created an extension 20" long, quite makeshift, but sufficiently good results to provide the above yes answer.

The extension consisted of a 20" long piece of 1/2" square aluminum tubing with a wall thickness of about 1/16". Unknown alloy, but probably mechanically similar to 6061. The modulus of elasticity of aluminum is about 1/3 that of steel, and may have a better damping factor.

Test was run with sockets that would slip over the tube.

Over a number of trials with the Craftsman click wrench I had no appreciable torque overshoot, and I made no effort to very slowly approach the click point. However, I did not go fast. I took several seconds to reach click. No effort to go very slow near click.

.
Click to expand...
The answer to the thread title is NO within what I believe to be the context of the question, which is torquing of electrical-connection bolts using conventional means and methods of completing such task. That means at the very least, no impact drivers or aluminum-tube driver extensions!
 
gar said:
171108-0740 EST

Following is an excellent discussion on fastener torque and tension.
http://www.hexagon.de/rs/engineering fundamentals.pdf
Click to expand...

is indeed an excellent read, but seems more for the engineer who will write the final torq # that goes onto the install paper.
it also explains some about lubrication, which is just a factor within the analysis methods provided.
 
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