Re: [Phys-l] Torque and wrenches - retry

[brian whatcott <betwys1@sbcglobal.net>]

Sorry about the misfires. I finally noticed my CTRL key was stuck down 
on a rich text note. Ho-hum.

Torque wrenches are typically fitted with a 1/4 in, 3/8 in, 1/2 in, or 
exceptionally, a 3/4 in square drive, so as to fit a variety of socket 
sizes. Conceptually, the handle applies a variable spring force against 
a rachet fixed to the square drive end, so that when sufficient torque 
is applied, the
detent slips from the ratchet tooth, a signal that the dialed torque has 
been reached.

The details of the detent diameter, and spring force are designed to 
allow this slippage at the rated torque.

A simpler, cheaper design still sometimes seen has a handle rod which 
bends with applied torque, the bent handle carrying a pointer to a scale 
which is seperately fixed to the drive end.

In a word then, the diameter at which the handle torque is resisted by 
the square drive  is not vital to its calibration.

Brian W

On 3/14/2011 4:37 PM, Paul Lulai wrote:
> Hi.
> I've got a lack of understanding regarding torque wrenches.
> My understanding is that torque is the product of the force and radial distance of the force.
> Torque wrenches will stop turning / start ratcheting when the torque is higher than the settings on the wrench.
> My question is, at what radius does the torque wrench measure the torque?
> Is the radius that of the bolt head?
> If the radius is that of the bolt head, would simply changing the head of a torque wrench (and the bolt you are using) affect the actual tightness of a bolt?
>
>
> Paul Lulai
> Physics Teacher
> St Anthony Village S.H.
> 3303 33rd Ave NE
> St Anthony Village, MN 55418
>
> 612-706-1146
> plulai@stanthony.k12.mn.us
> http://www.stanthony.k12.mn.us/hsscience/ 
>
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