[pianotech] boring, (was Hammer strike line)

[erwinspiano at aol.com]

 Ed 
  Thanks for the detailed and informative description of your protocol. You have answered my question and Nicks reply carries much weight too.
  Dale


Subject: Re: [pianotech] boring, (was Hammer strike line)




I wrote: 



>>I do calculate the bore distance to the slope. I do this by using a set of graduated "hammers" glued up to shanks and flanges.  Actually, the "hammers" are various lengths of the Renner slats, glued to the shanks at exactly 90 degrees.  By putting, say, a 49 mm "hammer" in the piano, I can simply lift it to the string, drop a square down along its edge, and instantly see if it is at right angles to the string. When I find the correct length, I know that upon contact, the hammer is at 90 degrees to the string, and the shank is parallel.  It is quick, accurate, and easy.  
 
After successfully confusing Dale, he asks: 


>>  What do you find the average amount of over centering to be ie. no. of MM s the center of the hammer shank rises above the center pin height?
  Also I am most curious as to your subjective opoinion about what discernable differences in sound..if any? 
    uhhh...and the shank is parallel to what zzzzactly?

         I don't usually calculate the amount of over centering, but I do know on the regulating bench, stock Steinway actions often exhibit (visually), the hammer going well beyond horizontal.  This is also reinforced by observing how the string grooves relate to the center of the strike point,(the center of the grooves are usually distal to the the center of the hammer), as well as the plane of the string cuts being obviously off from square to the hammer's centerline.  From the perspective of mechanical transfer of energy,  this causes waste, in the form of heat and flex in the hammer and shank structure. Is it important?  I can't say, but usually obedience to first principles ( in this case, energy is most efficiently transferred at 90 degrees), keeps efficiency at its maximum. My subjective opinion is that I get more power under FF when the hammer's axis drives directly into the string, but I have no way of measuring that.  
   I also don't know, given that the hammers contact point is far closer to one end of the string than the other, that it should not overcenter just a bit to compensate for the strings' angle to the hammer at its point of maximum displacement, since as the string is moved from a straight line it is no longer at the same horizontal place it is when motionless.  This is a nit, I know, so I don't pick at it too much. I can't imagine this displacement would be a factor in the low bass, or high treble, since the former is so long and the latter so minute in its string movement.  Is it possible that in the middle, under forte play, it could be discerned? Maybe. 
   If the hammer overcenters when new, it will progressively get more so as the hammer is worn/filed.  For this reason, I shoot for a 1 mm undercenter on the heavily used practice room pianos, so that during the life of the hammer it will go from 1mm under to exact and then on to  whatever overcentering the budget requries before replacement. If I begin with an overcentering arrangement, it simply gets worse and worse throughout the hammer's life. 
  If the hammer is at 90 degrees to the shank and 90 degrees to the string upon contact, the shank and string are parallel to one another. 
Hope this helps explain the obtuse fascination of an obsessive compulsive with minutia . 


Regards,

Ed Foote RPT
http://www.uk-piano.org/edfoote/index.html
  



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