Torque Wrenches - my answer...

[Bernard Littau]

In for a penny in for a pound, I guess.  Comments in line...

Huw Powell wrote:

>
>>>> ... The 2079 tool does in fact act as a force multiplier
>>>
>>>
>>> How does it do that?
>>>
>> Good question.  By lengthening the lever arm.
>
>
> But there is no lever arm lengthening going on.  If the business end 
> of the torque wrench were fixed solid to the 2079, there would be.  
> But it's not, it is a pivot point, with its axis fixed relative to 
> each tool, upon which the torque wrench is acting.

This is the fundamental problem right here.  One camp sees this as a 
simple lever arm lengthening, whilst noting that there is a potential 
pivot point that has no bearing on the problem.  The other camp is 
trying to complicate the problem by thinking too hard about the pivot point.

>
> Picture the microcosm of the meeting point between the two tools, if 
> you  will.  At that junction, there is a square hunk of metal, the 
> driving nub thing of the torque wrench, that is imparting a twisting 
> action to the 2079.  Each of the four faces of the "nub" are pushing 
> in different directions, 90 degrees to each other, but all 
> perpendicular to a radius drawn from the center of the nub.

True but pointless to the problem.

>
> In terms of its internal stresses, the 2079 is more like a chain drive 
> with a pair of equal diameter gears at each end, moving the torque 
> from its source to the fixed point at its other end.

This is fantasy.

>
> Another mental picture that is useful, to realize that even though 
> "torque" is described as a force on a lever in terms of its units, it 
> is not always translatable back to that concept, is to think of a 
> typical air driven impact wrench.  There is no lever arm, and 
> certainly no huge operator effort, and yet the tool can deliver up to 
> 600 ft lbs of torque at its little output nub.  A twisting force, or 
> torque, not a weight applied to a lever.

No, torque can always be translated back to a force on a lever.  The air 
impact wrench example is specious, as is much of the discussion on this 
matter.

The air impact wrench is banging a weight on a lever rather than pushing 
constantly on a lever.  The force on the lever is the result of an 
elastic collision between the weight and the lever.  The faster you spin 
(and bang) the weight, the more torque you apply.

>
> So, does anyone up here in snowy (!) New England have a 2079 kicking 
> around so I can play at some experiments and prove myself right or 
> wrong? (at least to my satisfaction...)
>
Please someone :-)

Best,

Bernard