Do extensions effect torque measurements?

[GoldDigger]

But extensions do not reduce torque.

As was fairly clearly described, the operating mechanism of an impact wrench delivers a fixed impulse to the socket. If the drive train to the nut is fairly rigid this impact will produce a high torque applied to the nut.
If the drive train, in particular the extension shaft is flexible, it will allow the impact driver output shaft to rotate farther during the drive pulse, thus reducing the torque applied to it by the impact driver. The torque as the nut will therefore be the same as the torque applied to the extension, but that value will be lower than the impact driver would have delivered without the extension.

 

[gar]

171103-1504 EDT

Smart $:

But to spring under force is a form of yielding.

Yielding in mechanical terms means irreversible change such that upon removing a force the item loaded with that force does not return to its original position or shape.

However, torque at each end of the [springy] extension is the same.

Not on an instantaneous basis. Everything is springy and has mass. Thus, a low pass filter in many cases.

When you apply motion to a springy device you do not get an instantaneous rise in force or torque. Everything is springy, just different spring rates.

In the real world you can not instantaneously apply a force or torque. However, you can say and have an initial condition of some force or torque.

.

 

[Smart $]

171103-1504 EDT

Smart $:

Yielding in mechanical terms means irreversible change such that upon removing a force the item loaded with that force does not return to its original position or shape.

Not on an instantaneous basis. Everything is springy and has mass. Thus, a low pass filter in many cases.

When you apply motion to a springy device you do not get an instantaneous rise in force or torque. Everything is springy, just different spring rates.

In the real world you can not instantaneously apply a force or torque. However, you can say and have an initial condition of some force or torque.

.

As I said, a form of yielding. I will accept the mechanical definition as the point at which deformation starts for our discussion.

Anyway, there is a simple test to prove what I'm saying, and it is quite similar to the method we use in nuclear power plants to verify calibration. Attach a torque wrench to both ends of an extension. With one torque wrench held stationary, apply torque with the other wrench. Read the force applied on both wrenches...

 

[GoldDigger]

As I said, a form of yielding. I will accept the mechanical definition as the point at which deformation starts for our discussion.

Anyway, there is a simple test to prove what I'm saying, and it is quite similar to the method we use in nuclear power plants to verify calibration. Attach a torque wrench to both ends of an extension. With one torque wrench held stationary, apply torque with the other wrench. Read the force applied on both wrenches...

That is a static measurement. The only place where the extensions were clearly described as reducing torque is the dynamic situation with an impact driver which has been described. And there the shaft reduces the torque produced by the impact driver, it does not make the torque lower on one end than the other.

 

[ggunn]

Everything is springy, just different spring rates.

As Devo puts it, we are living in a wiggly world.

 

[gar]

171103-1614 EDT

Smart $:

See https://en.wikipedia.org/wiki/Yield_(engineering)

Your torque wrench calibration method is a static method (steady state). Results can be quite different under dynamic conditions. This is why there are two different basic courses. One is called statics, and the other dynamics. Statics is a prerequisite to dynamics. Engineering materials covers stress-strain curves.

GoldDigger gave you a good explanation. Fundamentally the impact wrench is an impulse generator. The shaft (extension) and other mechanical components are a low pass filter. So on a dynamic basis you are concerned with the output response of a low pass filter to an impulse input.

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[Besoeker]

Good grief.............is this topic still going on??

 

[FionaZuppa]

Good grief.............is this topic still going on??

seems like it.

 

[Coppersmith]

I'm the OP.

I think this is a misconception carried over from the automotive world.

I've never used a torque wrench before. I've started using one because I see from the discussions here that we are now required to. The question was a purely original thought based on my new experience with the wrench.

no.

Not unless the axis of the extension ....

IMO from a practical perspective for common electrical connection it doesn't matter much.

So apparently the answer is no. Thanks!

 

[GoldDigger]

I'm the OP.



I've never used a torque wrench before. I've started using one because I see from the discussions here that we are now required to. The question was a purely original thought based on my new experience with the wrench.

So apparently the answer is no. Thanks!

Just for completeness before leaving the subject, note that the calibration of a torque wrench is based on the assumption that a concentric socket is used to engage the nut or bolt head.
If you take what is called a crowfoot adapter (essentially a stubby open end wrench with a square hole in the handle for the squared drive) you will have to apply a correction factor based on the ratio of the whole length (end of wrench handle to center of open end wrench divided by the length of the torque wrench handle alone (grip point to center of square drive.)

 

[K8MHZ]

Just for completeness before leaving the subject, note that the calibration of a torque wrench is based on the assumption that a concentric socket is used to engage the nut or bolt head.
If you take what is called a crowfoot adapter (essentially a stubby open end wrench with a square hole in the handle for the squared drive) you will have to apply a correction factor based on the ratio of the whole length (end of wrench handle to center of open end wrench divided by the length of the torque wrench handle alone (grip point to center of square drive.)

If I saw someone using a crow foot adapter with a torque wrench I would probably laugh out loud.

 

[K8MHZ]

I'm the OP.



I've never used a torque wrench before. I've started using one because I see from the discussions here that we are now required to. The question was a purely original thought based on my new experience with the wrench.







So apparently the answer is no. Thanks!

Your question was a good question. And you are correct, the answer is no. I spent many years in the automotive field and have used torque wrenches all along. There has never been an issue with using straight extensions.

FWIW, Harbor Freight has good click type torque wrenches. You just have to remember to un-twist them every time you are done using them.

 

[gar]

171103-2424 EDT

Looking back at the title of this thread, "Do extensions effect torque measurements?", the answer is ---
They certainly can. For an ordinary use by an electrician probably not.

Is the torque measurement by a reaction transducer identical to that of a rotary transducer? Identically no. Practically in some cases close, in other cases nowhere close.

Put two rotary transducers in series, or two reaction units is series. Will you get nearly identical results? Maybe, or maybe not.

Can you expect to get good torque measurements thru an offset driver. An offset driver is a gear box that transfers torque on one axis to a parallel axis. You could also have torque translators between angled axes. This is a bad approach and the transducer needs to be associated with the output axis.

Torque, force, and pressure transducers in an industrial application are likely to be something that some electricians will need to work with. Thus, a knowledge of their operation and interaction with an application is important.

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[ptonsparky]

I do know that when trying to break loose a rusted in screw with a 6” #2 Phillips fails, the 16” results in the screw breaking off or coming loose. I attributed it to the bit more angle equating to a longer lever.

When having to use extensions, I try to keep them in line, perpendicular.

 

[ggunn]

It seems to me that like a lot of other topics this one has run off the rails. I believe that the original question was that with a standard click type torque wrench, if you use a "cheater pipe" to extend the handle do you change the torque that the wrench applies before it clicks? The answer is no; the action happens in the head of the wrench and the length of the moment arm does not matter.

It can make it easier to overshoot the prescribed torque if you aren't careful, but the applied torque at the click point doesn't change.

 

[K8MHZ]

It seems to me that like a lot of other topics this one has run off the rails. I believe that the original question was that with a standard click type torque wrench, if you use a "cheater pipe" to extend the handle do you change the torque that the wrench applies before it clicks? The answer is no; the action happens in the head of the wrench and the length of the moment arm does not matter.

It can make it easier to overshoot the prescribed torque if you aren't careful, but the applied torque at the click point doesn't change.

His question wasn't about a cheater pipe, it was about using a 1/4" extension, 6" long between the torque wrench and the socket. Once the wrench stops, the torque at both ends of the extension will be the same. 200 inch pounds isn't enough to induce spring action into the extension at low speed, thus the socket end will stop at the same time the wrench clicks and not override it.

 

[gar]

171105-1114 EDT

ptonsparky:

My conjecture in your screw removal situation is:

You have a breakaway torque to be exceeded.

This torque will be greater than that of sliding friction after breakaway.

If you reach breakaway, but only move a very small amount have you really moved into sliding friction?

With a short driver there is not much shaft windup, and not much energy stored in the shaft. A longer shaft will have more stored energy in the shaft at the point of breakaway, and thus can maintain a moderate torque longer after breakaway thus getting to lower friction.

A separate question is whether your hand can produce as much torque with a shorter shaft, or couple it to the fastener.


ggunn:

I think K8MHZ provided a good comment on what appears to have been your understanding of the original post.

I don't think for ordinary electrical work that a shaft extension will cause any significant problem.

However, to have a real understanding of torque at different points in a mechanical system, then you need to consider the dynamics of that system.

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.

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[MAC702]

If I saw someone using a crow foot adapter with a torque wrench I would probably laugh out loud.

I do it all the time installing muzzle devices on rifle barrels.

 

[GoldDigger]

I do know that when trying to break loose a rusted in screw with a 6” #2 Phillips fails, the 16” results in the screw breaking off or coming loose. I attributed it to the bit more angle equating to a longer lever.

When having to use extensions, I try to keep them in line, perpendicular.

My guess: Either the 16" has a better handle grip or it lets you get into a position to apply more torque to it.
It may also have better fitting tip, but that would not cause the symptoms you describe unless you are holding back on torquing the 6" because the tip is about to slip.

Do you know about the difference between Phillips and PosiDrive?

 

[ptonsparky]

My guess: Either the 16" has a better handle grip or it lets you get into a position to apply more torque to it.
It may also have better fitting tip, but that would not cause the symptoms you describe unless you are holding back on torquing the 6" because the tip is about to slip.

Do you know about the difference between Phillips and PosiDrive?

My experience would be non scientific but i did try to use same position etc. Entirely subjective. Yes, I know the difference.