Torque Wrench Question

[DaveHess]

This one is for you master mechanics. I used to know the formula about 30 years ago but have since forgotten. Here goes... When using a crows foot with a torque wrench, what is the formula used to figure out what the torque wrench should be set at with the extra length of the crows foot for a given torque? My crows feet are not marked with a number (i. e. . 85, etc). Anybody remember this one?

 

[RustyJC]

L = length of torque wrench from center of grip to center of drive



O = effective offset of crow's foot, from center of drive to center of jaws as measured along the axis of the torque wrench



Torg = original torque



Tnew = new torque setting



Tnew / Torg = L / (L + O)



Solving for Tnew



Tnew = Torg x (L / {L + O})





Rusty

 

[DaveHess]

I'm such a mathmatician. This should prove to be interesting.....

 

[RustyJC]

Example:



L = 18"



O = 3"



Torg = 100 lb-ft



Solve for Tnew:



Tnew = Torg x (L / {L + O})



Tnew = 100 lb-ft x (18 / {18 + 3})



Tnew = 100 lb-ft x (18/21)



Tnew = 100 lb-ft x 0. 857



Tnew = 85. 7 lb-ft





Rusty

 

[Joe G.]

I think the torque setting will not change if the crow's foot is at right angle to the axis of the torque wrench.

 

[RustyJC]

I think the torque setting will not change if the crow's foot is at right angle to the axis of the torque wrench.

That's right - using the equation above, the offset O is equal to zero (0) if the crow's foot is at 90 degrees to the axis of the torque wrench.



Rusty

 

[DaveHess]

So, basically by attaching a crows foot to my torque wrench like I would with any other socket, I'd use the formula above to get the new torque. Am I on here?

 

[nickleinonen]

So, basically by attaching a crows foot to my torque wrench like I would with any other socket, I'd use the formula above to get the new torque. Am I on here?

yep up are