I have had mechanics and one person who builds competition airplanes swear that torque wrenches are inaccurate when an extension is added. To me, this flies in the face of the Action, Equal and Opposite Reaction Law. Just wondering if anyone has seen any explanation for this widely accepted phenomenon.I do quite a lot of my own maintenance to my vehicles and I consider recommended critical. I think about these claims every time I set my torque wrenches. I can see a possibility of error if a universal comes into play but with straight extensions I don't see it.

Maybe it's the potential to end up with the head of the torque wrench not directly above the bolt, particularly with a long extension. Or using your hand to support the extension adds a slight amount if drag.Edit: Either way, it's not enough to matter.

Impact gun, yesHand held torque wrench, no

Doesn't make much sense. If you have the torque wrench set at X lbs. then it doesn't matter how much the extension flexes or twists it is only going to show the lbs exerted on the wrench. You either are applying the correct torque or not!

Having spent 30 years in the missile building business, I can assure you we didn't adjust our torque values for any twisting action in an extension. Of more concern would be whether your torque wrench is properly calibrated or not. In our business, we would recalibrate torque wrenches every six months. On average 5% of them were out of the specified tolerance at this interval. How many home mechanics take their torque wrench out of the box, and never calibrate it for the life of the wrench?

I've worked on automotives for decades. Both professionally, and now, hobby wise. Have never experienced that, and don't buy it.Universals, yes. Simple extensions, no.If there is any inaccuracy, it will be minor, and likely within the margin of error of the instrument anyways.Here's an interesting article from Hot Rod Magazine about torque wrench myths and truths.http://www.hotrod.com/how-to/additional-how-to/ctrp-1111-torque-wrench-myths/Mike

Myth that socket extensions change torque wrench readings

89 Replies

red31
Explorer
Aug 06, 2015
Seems 3,4, 5 and Pythagoras are off topic also, didn't stop em!
mikestock
Explorer
Aug 05, 2015
Rope? Who came up with that analogy? How much torque are you applying to the end you are twisting? Torque is the subject of the discussion.
red31
Explorer
Aug 05, 2015
CJW8 wrote:
Take a take a piece rope, 1/2" diameter, 1" long. Hold it at both ends with fingers and twist one end 1/2 a turn. You'll feel it with your other hand. Now take the same piece if rope but 6 feet long. When you twist one end you'll likely not ever feel anything at the other end.

So you can FEEL 1/2 turn per foot but you can't FEEL 1/12 turn per foot? You need better measuring tool.

So I hand you a pre-wound rope, one end in each hand, which end had the 'applied' energy?
wnjj
Explorer II
Aug 05, 2015
Salvo wrote:
There's an error in that link.

The effective lever length "L" is not

It x Ia cos(a)

but

It + Ia cos(a)

wnjj wrote:

Here's a good diagram with equation. Note that at 90 degrees, L = It.

http://firetrucksandequipment.tpub.com/TM-9-254/css/TM-9-254_92.htm

Nice catch! Their plus had too much torque applied to it with a crowfoot and tipped over. :)
Salvo
Explorer
Aug 05, 2015
There's an error in that link.

The effective lever length "L" is not

It x Ia cos(a)

but

It + Ia cos(a)

wnjj wrote:

Here's a good diagram with equation. Note that at 90 degrees, L = It.

http://firetrucksandequipment.tpub.com/TM-9-254/css/TM-9-254_92.htm
NinerBikes
Explorer
Aug 05, 2015
I had a gal torque my nuts, once....
CJW8
Explorer
Aug 05, 2015
red31 wrote:
CJW8 wrote:
Lets imagine socket extension were 100 foot long. Will it not wind up, storing some of the applied energy?

What prevents the long extension from turning?

Instead of a bolt, what if the 'other' end had a torque gauge, both ends would measure the same static torque.

I don't think so. Take a take a piece rope, 1/2" diameter, 1" long. Hold it at both ends with fingers and twist one end 1/2 a turn. You'll feel it with your other hand. Now take the same piece if rope but 6 feet long. When you twist one end you'll likely not ever feel anything at the other end.
mikestock
Explorer
Aug 05, 2015
Just one thing: Wind up a 100' extension then something on the other end must supply an equal amount of resistance. True, the wrench may ratchet before the torque equalizes but it will eventually equalize or the load will keep turning until it does.

It's like taking an 48" spring with a handle on each end. Two people face each other and attempt to turn it in opposite directions. If one can apply 100 ft-lbs of torque and the other can apply 101 ft-lbs you know what will happen. They energize the spring to their maximum capability. Person number one cannot resist the extra ft-lb and his handle will turn.

Intended to let this thread die but couldn't help myself.
red31
Explorer
Aug 05, 2015
CJW8 wrote:
Lets imagine socket extension were 100 foot long. Will it not wind up, storing some of the applied energy?

What prevents the long extension from turning?

Instead of a bolt, what if the 'other' end had a torque gauge, both ends would measure the same static torque.
CJW8
Explorer
Aug 05, 2015
Lets imagine socket extension were 100 foot long. Will it not wind up, storing some of the applied energy? Heck, if it were that long, the wrench might click while at the bolt end doesn't even turn. Granted, a 4-6 inch extension will not wind up much and will store very little energy. If you are worried about it, always use the black extensions and sockets designed for impact tools. They are harder ans will not twist as much.