> Here you are talking about "good plate design," a design in which
> the bottom of the struts is close to the plane between hitch and capo,
> and there isn't much tolerance. That is one part of the picture. The
> other part of the picture is the soundboard and how it moves with
> humidity. I see no problem with the scenario that bridge pins are jammed
> against struts with an unloaded board, as long as this isn't an
> accidental result of having set bearing when the board was dry and at
> minimum crown. The word "accidental" being the operative word here. If
> it is planned, and that is producing the results you want, great! If you
> aren't paying attention and getting results that are all over the place,
> well, that's a different matter. Maybe you want results that are all
> over the place. ("You" being a generalized word, not directed at anyone
> in particular here).
In compression crowned soundboard assembly, setup, and
stringing, The plan rarely coincides precisely with the result.
To set the bridge height, the capped bridges are on the
soundboard and in the piano with the plate set to it's
presumed final height. Wedges are driven in between the struts
and bridges, "loading" the board. The board deflects to the
limit of compression of the panel, whatever that may be, as no
two boards will be precisely the same. In this state, the cap
thickness is determined by kerfing the top and running a
string across to determine "final" bearing. Details are
available in past Journal articles. The plate is then pulled,
the bridges planed to finish height, drilled, notched, and
pinned. When the plate is put back in for stringing the pins
may or may not contact the strut, and no one gives a rip
either way because it's not important. What's important,
initially, is where the bridge top is in relation to the
string plane as it was set by the wedging/kerfing/planing
operation. Once strung and at pitch, the pins aren't going to
contact the strut. Weeks or years later, the clearance between
pins and strut will increase as the board flattens, but as
long as the pins don't contact the strut, again, nobody gives
a rip. Whether or not the pins would contact the strut with
the strings off might serve as a very vague indication of that
the board has to offer in spring, but in itself, is useless
information.
> I've just always thought it would make sense to control
> humidity/equilibrium moisture content at the point of production where
> bearing is set. In the factories I have visited, that didn't seem to be
> the case. Maybe I missed something.
> Regards,
> Fred Sturm
Board MC is more and less important depending on the basic
design of the assembly.
Ron N
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