How is torque actually measured when using a torque wrench?

  • #1
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Main Question or Discussion Point

wqoF5KW.png

Take this picture for example. Assume this picture represents a torque wrench applying torque on a nut, and a force F is applied at the centre of the black handle perpendicular to it. The force applied to the nut is:

Torque = Fd

There are times when a nut is in a very inconvenient location and you can't fit a torque wrench on it. Sometimes, a crow foot extension will be able to reach it. The problem is, changing the lever arm changes the torque.

Case 1: The common knowledge is that if the extension is at 90 degrees to the torque wrench, the torque applied to the nut doesn't change.

Torque = Fd (regardless of x)
vIkcW7g.png


Case 2: I have also heard that in order for the torque to remain the same, the distance from the handle of the wrench to the nut should be kept the same as the distance from the handle to the pivot point.

Torque = Fy = Fd
D3nTfxw.png


Case 3: Distance for torque should be measured from the handle to the nut perpendicular to the force applied.

Torque = Fx
P3F38G1.png


What is the correct method to measure torque applied to the nut?
 

Answers and Replies

  • #2
Merlin3189
Homework Helper
Gold Member
1,512
622
Case 1 is correct. Case 3 is also correct, but is obviously less mechanically advantageous, unless it gets you round an awkward obstacle.
Case 2 is not correct. For this to work, the force would have to be perpendicular to y.
 

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