Crowning methods, was soundboards.

[Delwin D Fandrich]

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  -----Original Message-----
  From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On
Behalf Of Terry
  Sent: January 24, 2005 4:03 AM
  To: Pianotech
  Subject: Re: Crowning methods, was soundboards.


  > | ....The other
  > | end of the spectrum would be no panel drying at all, and ribs
cut/formed to
  > | the desired radius. I am not aware of anyone that is at that end of
the
  > | spectrum.
  >
  > Walter.

  Really? They rib with the panel equilibrated with room RH - somewhere in
the 9 or 10% moisture content range? And then they sell a piano in
Minneapolis? Any idea how those boards look after a few years and a couple
hundred cycles of high to low environment RH? Any increased tendency to
crack?

I misunderstood your comment. Walter is supposed to rib their boards with
the panel at 6.5% MC, +/- 0.5%. Not particularly low being just under the
minimum MC recommended by most glue and adhesive manufacturers.



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   > | I believe most soundboard manufacturers build hybrid soundboards -
that is
  > | the ribs will have some radius cut/formed into them (often the 60-foot
  > | radius one hears of so often) and the panel will receive a fair bit of
  > | drying prior to ribbing. Steinway even modifies the 100% compression
  > | crowning process by drying the panel, using flat ribs, but gluing them
to
  > | the panel in radiused cauls.
  >
  > The result of this is still a pure compression-crowned soundboard.
(Think about
  > it....)
  >
  > Del

  Absolutely. I understand that. Perhaps I chose my words poorly. I did not
mean to suggest that the Steinway grand soundboard was anything but 100%
compression-crowned, but rather was pointing out one variation of the 100%
compression-crowned method: ribbing with a flat rib in curved cauls, as
opposed to ribbing a flat rib and clamping to a flat surface.

Sadly I've had this discussion with several factory people who seem to
believe that by pressing flat ribs to a panel at, say, 6% to 7% MC, to
curved cauls does not constitute compression-crowning. But it does. The
results are exactly the same -- you end up with a pure compression-crowned
soundboard assembly. And, hence, my earlier response to you.

Del

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