[pianotech] key leveling with a curve

[Roger Gable]

John & Mark & et al,

John,
I would lean toward the belief that the strike line was designed on a curve to reflect the curve of the belly. If that is not the case, then certainly a straight line regulation would be in order. Keep in mind though, the increased base string wrappings would dictate somewhat of a curve. Whether it be by design or error, the fact of the matter is, they do come off the assembly line with the irregular string line.

Mark,
As to the hammer bore variation solving the regulation variation, I believe you are correct, but the fact of the matter is, the factories chose not the vary the bore distance. I would tend to believe that varying the bore distance would be a logistics nightmare and prohibit gang filing of the hammers, leaving them with the crowned key leveling technique to resolve the issue.

Roger Gable
  ----- Original Message ----- 
  From: Mark Schecter 
  To: pianotech at ptg.org 
  Sent: Sunday, October 17, 2010 12:30 PM
  Subject: Re: [pianotech] key leveling with a curve


  Hi, Roger.


  Your description implicitly assumes constant bore length, thus pushing string height anomalies down through the entire action. If you compensate by varying the bore length to result in constant shank height, you maintain blow distance but allow the rest of the action to regulate in straight lines as designed, no?

  -- Mark Schecter





  On Oct 17, 2010, at 11:43 AM, "Roger Gable" <roger at gablepiano.com> wrote:


    Et al,
    Try this theory:

    Given the string height is curved &
    Given the let-off matches the string height curve &
    Given the hammer height is curved to maintain constant hammer travel.
    The wippen heel to capstan line will be curved to reflect the hammer line curve.
    Now, the bottom of the key at the balance rail hole line must be curved to maintain a constant leverage arm length,
    and to maintain a constant angle of attack.

    If you think this theory is sheep-dip try placing a .007" balance punching under a key and notice
    how far the hammer rises and how much increased aftertouch is felt. You can compensate for the increased key dip by 
    simply adding front rail punchings, but you also will have to back down the capstan to restore hammer height, thus demonstrating
    that you now have a shorter lever arm.

    Roger Gable

      ----- Original Message ----- 
      From: PAULREVENKOJONES at aol.com 
      To: pianotech at ptg.org 
      Sent: Tuesday, October 12, 2010 2:01 PM
      Subject: Re: [pianotech] key leveling with a curve




      In a message dated 10/12/2010 2:16:57 P.M. Central Daylight Time, nelsong at intune88.com writes:
        Are there other reasons for curve leveling that I am missing?

      Correct me if I'm wrong (there's a dependable hope), but the most general argument I've heard is that it is to compensate for the greater playing of the piano in the middle and the compression over time of parts and underkey felts, etc. I can see the argument for mimicking the string plane curve (maybe), but the former argument strikes me as uncompelling. 

      P
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