tuning pin torque

[Mark Schecter]

Hi, Cy. In your quote below, I would point out that Don's example talks 
about the turning force (torque) exerted on the pin by the tension of 
the string. What he says is clear and correct, but the particular 
pound-feet numbers in his example don't pertain to measuring the torque 
required to turn a pin against the friction of the block, the subject of 
David's original question.

I guess I'm trying to clarify something about usage of the term 
"torque". We often seem to talk about torque, as if torque is an 
attribute a pin block has when a pin is sitting in its hole, more or 
less the equivalent of friction. But torque, in piano tuners' context, 
expresses how much force it takes to turn the pin against the combined 
load of string tension (if present) and friction in the block.

So, regarding your last question, the common unit cannot simply be the 
string tension, and tension doesn't equate to torque. But tension can 
supply the force portion of torque, if the tension is trying to rotate 
something around a center. The lever length supplies the distance 
portion of torque.

Multiply the pounds reading on the torque wrench by the length of the 
handle in feet or inches to get pound-feet or pound-inches.

-Mark Schecter


Cy Shuster wrote:
> 
  snip
> 
> Just to hijack this thread, I've always been curious about the exact
>  units for torque.  In rec.music.makers.piano, Don Gilmore (an
> engineer) wrote this reply.
> 
> I wrote:
> 
>> ...The force on a tuning pin is measured as torque, but just
>> considering string tension, I guess simple mass is the right unit,
>> as though a weight were hanging off the end of the piano (right?).
> 
> Hi Cy:
> 
> Yeah, tension is just in pounds.  Properly it's force (or weight),
> not mass, but that's just being picky.  One pound-mass on earth
> weighs one pound (exerts one pound of force downward) and since you
> probably won't be working on pianos on the moon, a pound is a pound.
> 
> Torque is the tension multiplied by the distance from the center of 
> rotation.  If the string has a tension of 150 lbs and the center of
> the string is .125 in. from the center of the tuning pin then the
> torque is
> 
> 150 lbs x .125 in. = 18.75 lb-in
> 
> To get lb-ft we can divide by 12 and get 1.56 lb-ft.  In the
> engineering world we call torque "pound-feet" instead of
> "foot-pounds" so that we don't confuse torque with energy.
> 
> Sorry to interrupt the thread with my nit-picking.
> 
> Don Kansas City
> 
> -----------------------
> 
> Thus it seems the common unit we use is simply the string tension
> (150 lbs.), while the proper (?) equivalent in torque would be 18.75
>  "pound-inches".  Yet the torque wrenches we use for tuning pins are
>  calibrated in pounds... right?
> 
> --Cy--
>