Torque 3

[jhampton1970]

Is there a formula to estimate the added torque needed when using an extension or elongated socket?

I was given a general rule of +10% for every six inches of extension from a seasoned millwright. Nevertheless, I have looked in the 26th edition of the machinery handbook, and a few other places, with no luck.

It is understood of the many variables i.e. surface friction, lubricants, etc. My goal is something in general.



Regards,
Jason Hampton
-Freedom isn't free!

 

[electricpete]

I believe you are mistaken... assuming the extension (crows foot) is on the socket end of the torque wrench. You guys correct me if I’m wrong.

I think it can be shown from a shear and bending moment diagram.
Let the extension be from x=0 to x=E
The wrench goes from X=E to X = E+L
L = original lenght
E = extension length

Apply the force +F at the right end (x=E+L)
Reaction force –F at the left end.
Reaction moment is
M(0) = F*(E+L)

Shear is –F througout the wrench and extension.

Moment is F*(E+L) at the left end of the beam (where the socket is) and decreases to 0 at the right end of the beam.

Moment is different at the left end x=0 where the actual extended socket is than at the normal socket position. The moment at x=E is “sensed” by the torque wrench. This is lower. The moment at x=E is given by
M(x=E) = [L / (L+E)] * [ F*(E+L)]

The sensed moment is [L / (L+E)] less than applied to the socket.
The actual moment is [ (L+E)/L] higher than the sensed (indicated) torque


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[Cockroach]

Wow, JHampton1970! You may just want to go western, i.e. cowboy, on the wrench and call it a day.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[ivymike]

okay, perhaps this post should be moved to the language/grammar forum for resolution:
* There are quite a few people who have decided (incorrectly in my opinion) that the OP was referring to an extension that effectively makes the handle of the wrench longer (like a cheater bar, crow's foot, or similar). All the engineers in here probably agree that such a device changes the moment arm and will change the torque "seen" by the bolt.
* As I've mentioned at least once before, the OP lumped deep sockets and extensions together in his question, which to me means that he's talking about extensions along the axis of rotation (like the 6-inch socket extension from craftsman, link above, or an elongated/deep socket, as in the orig. post). All of the engineers in here would probably agree that (excluding effects of tilting) these devices would not affect the torque "seen" by the bolt.

Would all the non-engineers, and any others who are still confused, please identify yourselves?

 

[ivymike]

(Fabrico and electricpete should decide whether they are talking about the same type of device before they continue their argument... my conclusion is that they clearly are not)

 

[telecomguy]

"All the engineers in here probably agree that such a device changes the moment arm and will change the torque "seen" by the bolt."

I agree, the cheater bar allows you to apply 'more' torque, but I don't agree that you need to make some adjustment in the "torque needed" (see the original question). If a fastener needs to be torqued 10 in-lbs, then apply 10 in-lbs. If you need a cheater to do it, then by all means use one.

The guts of a torque wrench have no idea how long of a handle you are using, nor for that matter, they don't care if you are holding the handle at the end or in the middle, or grabbing the head of the wrench and twisting it...

<tg>

 

[jhampton1970]

WOW, it seems that I have stirred up a hornets nest!

To eliminate confusion, I was referring to the socket type extension mentioned above by ivymike:

"you DO NOT apply a correction for the device commonly known as an "extension" (6in extension bar shown here

http://www.sears.com/sr/javasr/prod...cat=Socket+Accessories&amp;BV_UseBVCookie=Yes

)"

It seems there is a difference of opinion on this topic. Maybe I will have to do more research on this topic.





Regards,
Jason Hampton
-Freedom isn't free!

 

[electricpete]

I agree it's a matter of terminology.

I incorrectly interpretted who was talking to whom. (I thought Fabrico was responding to the post before his by CESSNO and therefore would have been talking about a crow's foot type device).

My apologies Fabrico.



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[IRstuff]

There is a tendency for poorly manufactured socket extensions to twist in the square socket, so there's perhaps some rationale for putting some extra torque on the torque wrench to make sure the fastener is getting the right torque.

TTFN

 

[telecomguy]

Just think equal and opposite. If the torque wrench is applying a torque, you can rest assured, the screw is receiving the torque.

<tg>

 

[Fabrico]

Silly me, epete! I assumed "Jason" in my post would refer to the OP named Jason. Then I went and assumed that the elongated socket he mentioned meant elongated longitudinally instead of sideways or oval(?). I'll be more careful next time. Now, where's that 20 foot crowsfoot wrench I was just using?


IRstuff that defies logic. No matter where a square goes inside of another square, it cannot transmit less torque than if it were centered.

 

[electricpete]

If that is how you respond to an apology, then I withdraw mine.

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[electricpete]

telecomguy - I agree with your conclusion for putting a cheater on the non-socket end of the torque wrench. But if you apply a crow's foot, the scenario changes and the torque wrench no longer indicates the torque applied.

Different subject - At the end of my first link above there was someone who was suggesting a correction for the type of extender that we're calling an elongated socket.

I think that is incorrect but I can see how someone may mistakenly come to that conclusion.

If the torque wrench is length L and I extend the socket length E in a direction, then mathematically there is some basis to develop a reduced calculated torque. If I apply a force F at the end of length L, the torque transmitted to rotation of the bolt is no longetr F*L. It is something like F*L *sqrt(L^2-E^2). There are two errors with this approach as I see it:
1 - The above calculation assumes force is applied at the end but no counterforce at the socket (as if you were operating with one hand)., The correct procedure uses two hands with the other hand applying counterforce.
2 - Even though the torque is less than F*L, if the torque sensor sees this reduced torque and properly indicates it than there would be no need for a correction. I think the torque sensor would see this properly and no correction would be required (even assuming we applied torque improperly with one hand), but I'd be interested to hear what others say.

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[electricpete]

I left something out... please add correction as shown in bold:

"If the torque wrench is length L and I extend the socket length E in a perpendicular direction"

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[electricpete]

ivymike - you were 100% correct in your assessment of the terminology. You made the statement:

"All the engineers in here probably agree that such a device changes the moment arm and will change the torque "seen" by the bolt."

While I agree with the conclusion I don't agree the logic listed in that sentence is sufficient to reach the conclusion. The relevant comparision is not whether torque changes for a given force applied (I believe the perpendicular extension applied with one hand will result in a change in torque for a given force applied). The relevant comparison is the torque applied vs torque indicated. For that we have to consider the mechanism used to sense torque. I believe it senses the moment in the wrench at the normal position of the socket, which provides the basis for my discussion above.

I have the highest respect for you and I am positive you easily understand that concept if you didn't already have that logic embedded as an unstated assumption of your comments. On the surface it sounds like you are saying that what I said was trivial. That will depend on the perspective but I just wanted to clarify the basis is not so simple as conveyed in your words.


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[electricpete]

Thinking some more, I think my comments about the perpendicular extension were off base when I suggested that if you applied torque with one hand without countertorque you could get reduced torque.

I drew a vector diagram length L, perpendicular lenght E, hypoteneuse R.
R^2 = E^2+L^2

Now add a force F at the end of L, perpendicular to all 3 distance vectors. We have a right moment triangle with sides F*L, F*E and hypoteneuse F*R.

I got distracted before by the fact that F*LF is less than F*R. But that is not relevant. F*L is the relevant torque, it's the expected torque, it's the torque applied to rotating the nut, and it's the sensed torque at the socket position. All the sane as expected. Sorry I made that one more difficult than it needed to be.

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[John2004]

Hey everyone,

I used to work for Goodyear & they used "Torque Sticks" to tighten lug nuts to specific torque’s.

You can see them and read about them here...

http://www.procutinternational.com/html/torqstik/torqstik.html

These torque sticks were just solid socket extensions that went on the end of an pneumatic impact wrench. There is no clutch or anything that "slips" at a certain torque. You just put the torque stick on the impact wrench, and then the lug nut will not be over tightened.

You would not think the length or diameter of the extension (parallel to the axis of rotation of the nut) should really effect torque, but with the torque sticks, it does.

I am still not 100% clear on how these things work. Can anyone explain it better than the link I gave?

It seems it must have something to do with being used with an air operated impact wrench and not a standard torque wrench. However, whether it comes from an impact, a standard torque wrench, a lever, or whatever, it seems torque is torque ?

Thanks
John

 

[IRstuff]

You should look at the link on the page you provided:

http://www.procutinternational.com/html/torqstik/how_torqstiks.html

Basically, it's a spring that operates like a low-pass filter on the torque pulses provided by the impact wrench.

TTFN

 

[John2004]

Hi IRstuff,

I think I see now, the "torqstik" will only work with an impact becasue the torqe is turning on an off very fast. The torqstik acts like a torsion rod or spring, and the torque at the nut-end does not have a chance to catch up with the torque at the drive-end before the impact turns off each cycle or impact.

It would not work with a manual lever or standard hand operated wrench.

I think it's a clever idea. Wish I would have thought of it.

Thanks
John