Plywood shrinkage??? Laminated soundboards???

[Delwin D Fandrich]

> -----Original Message-----
> From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On
> Behalf Of Sarah Fox
> Sent: February 14, 2004 8:28 AM
> To: Pianotech
> Subject: Re: Plywood shrinkage??? Laminated soundboards???


>
> Dunno...  Is there anything different that distinguishes laminated
> soundboards from plywood, besides the quality of wood, of course?

Price.


>
> Assuming that there *is* shrinkage over time, this would be a
> problem for a
> compression-crowned system, if such beasts (compression crowned, laminated
> panels) exist.  However, for rib-crowned, it would be a lesser problem,
> provided the SB doesn't shrink so far as to slip off of its support.  Of
> course there would be a nasty problem of glue joint failure, and
> traction on the SB (while still stuck) might diminish crown somewhat.


Laminated soundboards MUST be rib-crowned. More than one manufacturer has
failed to failed to appreciate this basic fact. And it is one of the reasons
laminated soundboards have gotten such a bad rap in the industry. There has
been very little actual research and development effort applied to the
technology. Even basic engineering has been sadly missing. Most of the
laminated soundboards out there have been run down the same assembly line,
using the same ribs and the same presses, as their solid-spruce
counterparts.

Shortly after I went to work at Baldwin I was asked to look at a "few"
vertical pianos that had been returned to the factory with "buzzing
soundboards." The problem turned out to be ribs resting -- or, worse, not
quite resting -- against the backposts. No one could figure out what had
gone wrong since "nothing had changed" in the production process. Nothing
ever changes, pianos just go bad all by themselves. As it turned out nothing
had changed except that these pianos had been built with laminated
soundboard panels instead of solid-spruce panels.

At the time Baldwin's soundboards were compression-crowned. But Marketing
had decided they wanted a price-leader model so between themselves and the
factory they had come up with this whole new model based on an existing
plate and scale. The one difference to the back assembly was the switch to a
laminated soundboard panel. Now, this laminated panels were treated just
like the solid-spruce panels which were still being run simultaneously on
the same back assembly for other models of the same size. Hence, the claim
that "nothing had changed...." They were carefully conditioned to
approximately 4% MC and ribbed in the normal manner. Of course, they didn't
belly in the normal manner, but no one seems to have noticed that. There was
a small problem with plate setting because the operator could not get normal
string bearing but that was deemed to be a plate problem and so the bosses
that established plate height were trimmed back at the foundry. Now, with
their "proper" string bearing, the pianos were strung, chipped and shipped.
With no crown to speak of the steady string bearing against the bridges kept
pushing the soundboard assembly back until the ribs began buzzing against
the backposts. What a surprise!

Even a minimal amount of thought aforehand would have prevented the return
and remanufacture of countless pianos. I continue to be amazed at the lack
of even the most basic knowledge and understanding of wood and its
characteristics found in many piano factories. Baldwin was not at all unique
in this.

As for your reference to the "shrinkage" of laminate decks on boats: whether
or not a plywood (or laminated) panel will expand or contract depends on the
moisture content of the wood at the time of layup. Dimensional contraction
(or expansion) is governed by changes in moisture content, not time.
Laminate panels will respond to moisture content changes much like solid
panel, they just do so far more slowly. So slowly, in fact, that seasonal
changes are generally not noticed. If, however, the panel was glued up at a
relatively high moisture content it will undergo some normal shrinkage over
the years, ultimately reaching some relatively stable dimension as
determined by local climate.

Del