Bridge dimensions

[Delwin D. Fandrich]

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  ----- Original Message -----=20
  From: David Love=20
  To: pianotech@ptg.org=20
  Sent: Saturday, March 29, 2003 8:34 PM
  Subject: RE: Bridge dimensions


  Perhaps it was a misinterpretation of your previous post on the =
subject, but I though you said that part of the reason for undercutting =
the bridge was to allow that part of the sound board to be able to move =
freely up and down. =20

Well, it's not going to be completely free, but it does need some =
freedom of motion.=20

  That prompted my question as it seemed that freedom to move up and =
down and stiffness, i.e. high impedance, were at odds.  I think you've =
answered that question, but if the board is going to move anyway, why =
bother to undercut the bridge other than to move it away from the =
bellyrail?  Is it assumed that on a piano with a more severely undercut =
bridge, it should have a more substantial rib configuration to balance =
it and vice versa? =20
Ah. I think I see the question. Actually, through the high treble the =
ribs are pretty much superfluous. The bridge body is so close to the =
bellyrail--actually the soundboard liner--that the bulk of the required =
stiffness comes from the soundboard itself. More or less, depending on =
the grain orientation (relative to the bellyrail) and the thickness of =
the soundboard. It is not until the bridge gets some distance away from =
the bellyrail that the ribs  begin to have any real effect.

  And given the choice between more mass in the bridge or more substance =
in the rib configuration, what would you choose?  Am I right in assuming =
that the more minimal undercutting in a Steinway bridge is because the =
rib configuration is more skimpy? ! If so, then would undercutting the =
bridge further on a Steinway create more problems and a weaker treble if =
the rib pattern and height remained the same?
Some Steinway bridges are minimally undercut. Others have had the =
bejeebers whacked out of them. We've just replaced one on an L that was =
cut back to no more than half of its already rather narrow width (mostly =
less than 30 mm throughout) and was taken down to 24.5 mm high at C-88. =
By mounting the plate so that the treble end was brought up to the same =
height as the bass end (i.e., with the pinblock uniformly thick across =
its width) the height of the new bridge is going to be about 30 to 32 =
mm. I expect sustain will be a bit better

I haven't done a whole lot of work on the theory of balancing the bridge =
dimensions off against the rib dimensions. I've evolved a balance that =
works and try to stick with it. One of these days....

Del
Delwin D Fandrich
Piano Designer & Builder
Hoquiam, Washington 98550 USA
360.532-2563
360.532-6688
pianobuilders@olynet.com


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