Bridge design

[Keith Roberts]

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Re: Bridge designSorry Del,
I thought the discussion had gone to the treble end of the long bridge. =
I haven't seen a transition bridge setup yet but I'm sure I will soon.
    A laminate structure is far more resistant to flex. Bend too =
straight pieces of wood and glue them together. They want to stay where =
you glued them and will stay that way longer and with less warpage than =
a piece of solid wood cut that way. (presuming the glue joint....etc.) =
I've been in the construction trades 30 years and a laminate beam is far =
more desirable structurally than even pattern nailing a bunch of boards =
together.
    Now here's where I may be presuming two much. It seems to me, as the =
bridge is loaded and the soundboard/bridge structure approaches the =
point of failure, the impedance would change exponentially. Small =
initial changes can become major. In my limited experience I haven't =
heard of any real model test of 2 identical boards and bridges glued up =
and run through a battery of tests. It was my feeling (my 2 1/2 years of =
engineering at UCSB is now a jigsaw puzzle with a bunch of missing =
pieces), that the glue joint as a variable might not have been coorectly =
assessed.
Keith R
Conrad!  You better throw in a technical disclaimer along with the =
automatic reworder on my new flame suit.
And HURRY!

----- Original Message -----=20
  From: Delwin D Fandrich=20
  To: pianotech@ptg.org=20
  Sent: Sunday, July 07, 2002 7:20 PM
  Subject: Re: Bridge design



    ----- Original Message -----=20
    From: Keith Roberts=20
    To: pianotech@ptg.org=20
    Sent: July 06, 2002 7:52 PM
    Subject: Re: Bridge design


    Maybe gluing the bridge cap on in the crowned position and the =
bridge to the sound board in the crowned position, like Dale does, will =
add the necessary impedance to the treble end of the bridge.=20
  It's not the treble end of the long bridge that is in question here. =
It's the bass end of the long bridge. And no amount of crowning the =
bridge to match the crown of the soundboard is going to affect that. Or =
much else, for that matter.



    Most of the models discussed here on the list, didn't seem to deal =
with the  stiffness added by the glue joints in a laminated structure. =
Usually underestimated and throws that kink into the reality/theory gap =
along with a few of the other observartions Dale has made.
  Would you care to explain this a bit more? How does stiffness added by =
the glue joints in a laminated structure -- assuming there is any -- =
affect the impedance of the very end of the long bridge?

  Del

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