tuning pin torque

[Cy Shuster]

  ----- Original Message ----- 
  From: Farrell 
  To: Pianotech List 
  Sent: Thursday, July 20, 2006 10:15 AM
  Subject: Re: tuning pin torque


  There will certainly be some variation of opinion on what "acceptable" tuning pin torque might be, but maybe about 60 to 150 in.-lbs. (note: inch-pounds, not foot-pounds) will yield a reasonable-tuning piano. 

  Terry Farrell
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--
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