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Hello there guys and Gals I have a question for you all and believe me it gets tricky...

A friend of mine had to make a special Crowsfoot spanner to tighten the base studs on his Panhead Harley.

Once he had made it he then proceeded to measure the length of his torque wrench and enter this figure into a formula in order to work out what he should actually set the poundage at on the torque wrench to tighten the fastener properly.

We ended up with a VERY longstanding (But Friendly) disagreement when I pointed out that the length of the torque wrench shouldnt matter...afterall it is designed to "Click" when the Set poundage is being transmitted through the centreline of the drive end of the wrench.

He poo pooed this idea and looked at me as if I was stupid.

I said that surely if I wanted to use the Crowsfoot on my bike then all I needed to do was borrow it and use my own torque wrench set to the same poundage as his had been and we would get the same result...He agreed...but then I pointed out that my torque wrench is a different length to his and so if I put my measurements into his formulae then we would have a different answer, so bearing in mind that we both used the formulae correctly then why do we have different answers to the same problem!!!!!!!!!!!!!!!

Furthermore, I ask, how does the torque wrench length matter when I can hold the handle ANYWHERE along its length and (Provided I have sufficient strength) it will tighten a fastener to the setting dialled in on the scale????????????

Unfortunately I am not good enough with my maths to figure this one out.

I am not saying that EVERYONE who does it the USUAL way are wrong, I am saying that there must be a way of figuring this out WITHOUT the length of the torque wrench being involved although I do accept that the effective length of the Crowsfoot from centreline of the fastener to centreline of the Torque wrench output is very much necessary.

It is a very difficult question to explain in typing and doubtless I have confused far more than I have managed to get to understand my query, but PPPLLLEEEAAASSSEEE can a mathematical brain tackle this?

Thanks for your time folks
 

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Full Bloody Rebel!
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Yep, clear as mud o_O
Crowsfoot offset matters, length of wrench doesn't. Well that's how I see it.

Chaley
Agreed! Once set, the torque can't change irrelevant of the length ('cos it's spring loaded, and set in Nm or lbft- force x length). Crows foot offset will affect it a little
 

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The torque is the force required to turn the Nut/Bolt against a fixed object. The torque wrench will 'click' at a set point against the fixed object no matter what the length of the torque wrench. It will be easier to get to the set torque with a longer wrench but the actual tightness will be the same no matter what the length is. Thats how I see it anyway.
 

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One of the jobs I do at work is to calibrate torque wrenches ..
most torque wrenches are only within 10% of the actual reading but this may increase or decrease in the lower,middle or upper ranges
The way to look at your general torque wrench setting is as guidance only .
 

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Nowheresville
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I think he's right. It's a bit early in the morning for my brain, but there are lots of online and downloadable calculators for this, including:

Torque Wrench Extension Calculator
Extensions Calculator « Support Library « Van F Belknap Company

Most of them showed a wrench with a dial indicator rather than a breaker type, but I think the calculation is the same because the spring that sets the 'break' is based on the length of the handle. Also, none of the ones I viewed mentioned any difference for breaker or pointer types so assume it is the same whatever the type.

Or is it . . .
 

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Got salt
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The torque wrench itself is calibrated to click at X foot-pounds of torque; equivalent to X pounds of weight applied to a foot-long lever. It could equally be one pound of force applied to a lever of X feet.

A crows foot fitted to the torque wrench adds additional leverage; if its 2" long, then the torque measured would be in 14 inch-pound increments not 12 inch-pound (one foot-pound).
 

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Grown up? Never!
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I think he's right. It's a bit early in the morning for my brain, but there are lots of online and downloadable calculators for this, including:

Torque Wrench Extension Calculator
Extensions Calculator « Support Library « Van F Belknap Company

Most of them showed a wrench with a dial indicator rather than a breaker type, but I think the calculation is the same because the spring that sets the 'break' is based on the length of the handle. Also, none of the ones I viewed mentioned any difference for breaker or pointer types so assume it is the same whatever the type.

Or is it . . .
Surely if that was the case the torque reading is only correct if you hold the very end of the handle? What if you've got massive hands and your grip takes up half the wrench? Where do you measure from?
;) :) ;)

Chaley
 

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Gym Junkie
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Surely if that was the case the torque reading is only correct if you hold the very end of the handle? What if you've got massive hands and your grip takes up half the wrench? Where do you measure from?
;) :) ;)

Chaley
Makes no difference where you hold the handle, it will just change the amount of effort required to achieve a given amount of torque:

 

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The length of the torque wrench is irrelevant, the extra length provided by the crows foot is all that you need to know.
If you have a 2 foot bar and put a 1 pound weight on it, you are getting 2 lbs/ft of torque at the end. If you extend the bar by a foot, you'd get 3 lbs/ft.
 

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Non of it makes a difference...all a torque wrench does is give you repeatability and consistency, this is not achievable by using a spanner or socket and your arm, you think you are applying the same torque but you are not

So if a torque wrench reads high or low so long as it always reads the same % of error it provides consistency

An expensive/quality (not necessarily the same thing) will provide a reading closer to the required figure but still out by a %
 

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I've decided that as the torque wrench spring/breaker is calibrated to the particular length of handle then the same formulars apply, so have to agree with your mate. He also appears to have good taste in motorcycles, so he must be right.


But, my name isn't Mr. Norbar . . .
 

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Non of it makes a difference...all a torque wrench does is give you repeatability and consistency, this is not achievable by using a spanner or socket and your arm, you think you are applying the same torque but you are not

So if a torque wrench reads high or low so long as it always reads the same % of error it provides consistency

An expensive/quality (not necessarily the same thing) will provide a reading closer to the required figure but still out by a %
THIS IS THE BEST ANSWER YET.
As I have already said the Torque wrench scale should be used as guidance only .
there are other factors that may affect torquing a bolt to the correct setting such as the amount of force required to turn a bolt into a threaded hole
so such as a worn bolt, interference between the male and female threads ,any lubrication on the threads, fitted with a washer or not.
on top of this I have seen people pull passed the click.
The difference therfore between using a crows foot or not, will be negligible.
 

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One of the jobs I do at work is to calibrate torque wrenches ..
most torque wrenches are only within 10% of the actual reading but this may increase or decrease in the lower,middle or upper ranges
The way to look at your general torque wrench setting is as guidance only .
we make torque wrenches for the like,s of F1 teams and work to 3% , as for handle length all ours are calibrated at a set point on the handle and yes moving up the handle gives a different reading , we also train our new people to " get the feel " of a tool as newbies tend to snap a tool which gives false readings.
 

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I've had another think about this and what I believe your friend to be saying is that to calculate the extra torque provided by the crows foot extension, you DO need to know the length of the torque wrench. You'd need to work out the extra length as a percentage of the length of the wrench - if it adds 10% length and therefore 10% move leverage, you'd need to adjust the torque setting down by that amount.
The length of a torque wrench as such, and where you apply the force to it, are irrelevant to the torque generated at the end, as long as it's calibrated correctly.
 
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