Do extensions effect torque measurements?

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Coppersmith

Coppersmith

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Electrical Contractor
I'm using a 1/4" torque ratchet wrench with a 1/4" x 6" extension for up to 200 lb-in. I'm wondering if the extension has any effect on the torque measurement since there might be subtle twisting.
 
Well, you would have to read the book that came with the wrench to satisfy the AHJ. But from a physics point of view - no.
 
I think this is a misconception carried over from the automotive world. When doing wheel lugs at 250 ft/lbs there may be some torsion in the extensions that causes inaccurate torque at the fastener. But we just don't apply anywhere near that amount of torque.

When I heard this I tried it out by putting together about 3' of extensions and torquing a bolt to 100 ft/lbs. I scribed the bolt position and then re-torqued it directly: If it turned at all, it was less than visible with the naked eye.
 
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Not unless the axis of the extension angles such that it displaces the point of connection off of the axis of the fastener. Hard to explain without a diagram and I'm too lazy to make one.
 
IMO from a practical perspective for common electrical connection it doesn't matter much.
 
retirede said:
Not unless the axis of the extension angles such that it displaces the point of connection off of the axis of the fastener. Hard to explain without a diagram and I'm too lazy to make one.
Click to expand...

I'll try a description:

If the extension is a loose enough fit on the fastener that the axis of the extension can lean either toward or away from the far end of the torque wrench handle it will make the effective length of the handle longer or shorter respectively.
You can pretty well negate this effect by using your other hand to keep the extension perpendicular to the surface while torquing.
 
retirede said:
Not unless the axis of the extension angles such that it displaces the point of connection off of the axis of the fastener. Hard to explain without a diagram and I'm too lazy to make one.
Click to expand...

Translation: bent extension :cool:
 
GoldDigger said:
I'll try a description:

If the extension is a loose enough fit on the fastener that the axis of the extension can lean either toward or away from the far end of the torque wrench handle it will make the effective length of the handle longer or shorter respectively.
You can pretty well negate this effect by using your other hand to keep the extension perpendicular to the surface while torquing.
Click to expand...

Yep - you described it much better than I did. Must be the bourbon :)
 
If you're doing it by hand (steady-state) and keeping everything aligned, there will be no effect.

If you're using an impact wrench, there will be some reduction of torque. Each impact has a constant amount of energy, not torque. Some of that energy will go toward tightening the fastener; some of it will go toward winding up the extension. (which is then released as soon as the impact is complete)

That's how torque-limiting extensions work. (which will not limit torque when using a hand wrench)
https://store.snapon.com/Torque-Extensions-5-pc-Torque-Extension-Set-P645206.aspx

Remember that a fastener torque measurement is only valid while the fastener is in motion.
 
1/4", 200lb-in ?? and the accuracy spec on that wrench is ?? nothing to worry about, the inaccuracy in the wrench is big enough to not worry about your extension inaccuracy factor.

in general, torsion will still transfer from one end to the other, it just means more rotation is needed.

also curious, is 200lb-in at the end of the scale on that wrench?
 
171103-1021 EDT

Define "extension", then define "torque extension", "torque limiting", and "torque limiting extension".

What is the theory of a "torque limiting extension"?

If you apply a slowly increasing torque to a "torque limiting extension", then what does the output torque look like? Does it abruptly limit at the extension rating like a slip clutch does?

If you do not know the theory of operation of a device, then you may not know how to properly apply a device. This applies to all sorts of devices. For example "dimmers".

.
 
retirede said:
Not unless the axis of the extension angles such that it displaces the point of connection off of the axis of the fastener. Hard to explain without a diagram and I'm too lazy to make one.
Click to expand...
GoldDigger said:
I'll try a description:
If the extension is a loose enough fit on the fastener that the axis of the extension can lean either toward or away from the far end of the torque wrench handle it will make the effective length of the handle longer or shorter respectively.
You can pretty well negate this effect by using your other hand to keep the extension perpendicular to the surface while torquing.
Click to expand...
junkhound said:
Translation: bent extension :cool:
Click to expand...
retirede said:
Yep - you described it much better than I did. Must be the bourbon :)
Click to expand...
Junkhound described it quite succinctly. Torque is a measure of how much a force acting on an object causes that object to rotate. If the torque measurement device is off-axis with the rotation of the object, the measurement will increase in inaccuracy with the angle of deflection.

Additionally, as long as extensions are on axis and provide no resistance to the object under measurement's rotation, the measurement will retain the same accuracy as the no-extension measurement.
 
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171103-1328 EDT

Smart $:

You just named it.

Slowly apply torque to one of those springy extensions or any conventional extension and torque is only limited when something yields or breaks.

.
 
gar said:
171103-1328 EDT

Smart $:

You just named it.

Slowly apply torque to one of those springy extensions or any conventional extension and torque is only limited when something yields or breaks.

.
Click to expand...
But to spring under force is a form of yielding. However, torque at each end of the [springy] extension is the same.
 
Smart $ said:
Care to offer or suggest a correctly named springy extension? :angel:
Click to expand...

Call them torque reducing (not limiting) extensions for impact wrenches. They would not be labelled with a particular torque value since that would depend on the specifics of the wrench involved.
 
GoldDigger said:
Call them torque reducing (not limiting) extensions for impact wrenches. They would not be labelled with a particular torque value since that would depend on the specifics of the wrench involved.
Click to expand...
But extensions do not reduce torque.
 
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