Torque & adapters (academic)

[eesof4@pcserv1.dseg.ti.com (EESOF student 4)]

This is going to be my only post on the subject and I will try to make it 
short.  Hopefully it will clear this mess up for good :)

To compute the actual torque on the crankshaft bolt when using an extension,
one must treat the torque wrench and the extension as two separate beams.

Looking at the torque wrench, on the handle end it receives a force applied
by the hand which I'll assume is perpendicular to the wrench.  On the other
end, it receives a force by the socket equal to, but oposite in direction to 
the force applied by the hand. It also receives a moment from the socket equal
to the force times the lenght of the torque whench (and this is the torque
that is indicated in the torque wrench).

Now, we must look at the extension.  First, on the torque wrench end, it
receives a force equal to the force applied by the hand in some direction.  It
also receives a moment equal to the torque indicated in the torque wrench.
Finally, on the crankshaft end, this extension receives a force equal to the 
force exerted by the hand, but oposite in direction, as well as some moment.

This moment must neutralize the other moments in the extension, which are: 
1) the moment exerted by the torque wrench (the torque indicated on it)
2) the perpendicular force exerted by the torque wrench (hand) times the
   lenght of the extension, (multiply by the cosine of the angle between the 
   extension and the torque wrench to get the perpendicular componet)

Which leads to the final equation of torque at the crankshaft bolt:

  T_crankshaft = T_torquewrench + (F_hand*L_extension*cos(theta))

Sooooo,

 1) The lenght of the torque wrench _does_ make a difference.
 2) The alignment between the torque wrench and the extension also make
    a BIG difference.

Note that if the torque wrench is perpendicular to the extension, the torque
on the crankshaft is the SAME as the torque on the wrench , which could lead
to a severely undertorqued bolt!!

Hope this derivation wasn't too long and settles the subject for good.

Later,

Luis Marques
marques@ti.com
'87 4kcsq