String Spacing on Bridge

[Delwin D Fandrich]

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  -----Original Message-----
  From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On
Behalf Of Michael Spalding
  Sent: January 25, 2005 7:41 AM
  To: Pianotech
  Subject: RE: String Spacing on Bridge


  Terry,

   (1) For a given piano length, lessening the string spacing would shorten
the low tenor strings.  Not a positive change in most piano scales.   (2)
Also, the heavier low tenor wires put a higher side force on the bridge pins
due to their stiffness, so larger pins and wider spacing would reduce the
bridge's tendency to crack.   (3) Bad grain orientation aside (Knabe) most
bridge cracking occurs around the closely spaced small pins in the high
treble, or on the bass bridge where string tensions are greatest.  I could
imagine that these factors were discovered during the transition from
parallel-strung to overstrung designs, and also as string tension increased
as cast iron plates were incorporated.

  Mike

1)    This depends on many factors including, but not limited to, the
placement of the bass bridge. In considering questions like this it is
helpful to clear the mind of preconceived notions and traditional design
practice that has become common but for which much more elegant solutions
may exist.

2)    The "heavier low tenor wires" do not place a side load on the bridge
pins that is significantly higher than is found in the upper tenor and
treble. Besides, the diameter of these pins is usually larger which reduces
the side stress bearing against the wood bridge cap.

3)    Starting the string flare (relative to the strikeline) higher up in
the scale provides much needed extra spacing between the bridge pins in the
upper tenor/lower treble region, surely a good thing.

Del

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