agraffes on bridge? (intentionally un-crowned boards?)

[Clark]

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Does the Stuart & Sons grand have agraffes on the bass bridge? I remember a post
inquiring about the use of ceremics in this piano, and a photo on their page
makes it appear to have them.
http://www.newcastle.edu.au/department/fmu/stuart1.html

I posted a few months ago about a repair to an agraffed Sohmer grand. This
unfortunate design has the sunk agraffe imparting down bearing, with a bridge
cap behind it to provide up bearing. The resulting twisting, _rolling_ force had
broken four ribs and fairly well pulled the soundboard in half. The repair
consisted of splicing maple caps into the ribs and sinking screws through them
into the bridge.

The repaired instrument is lively to the point of being unmusical; I assume the
agraffe string termination is so effective that there is no particular damping
of higher partials. The Hallet & Davis in the shop is not playing, so I can't
compare the sound but the bridge and soundboard are in much  better condition
than the Sohmer.


I have a question about the H&D design, in view of Del's post; it was implied or
stated earlier in this thread that the H&D design features an uncrowned (UC)
soundboard, and with the alternating up/down bearing agraffes this makes the
bearing on the board effectively zero.

If it so designed, the soundboard assembly is unstressed, in the sense that
RC/CC soundboards _are_ stressed from the loading by the strings. In the latter,
the loss of crown implies in some sense a structural failure and so a loss of
elasticity; the strings keep the now less elastic unloaded structure at
equilibrium through side bearing and the slight down bearing of the angled
bridge pins. In turn, this should make a less effective termination for the
speaking lengths than when the bridge provided up bearing because the strings
now account for the overall elasticity.

On the other hand, an UC board with alternating up/down bearing agraffes would
provide proper termination in this situation and the UC assembly resists upward
and downward motion equally,  with less overall elasticity than the loaded RC/CC
board but superior in the long run without the loss of termination, and so tone
which characterizes the collapsed board. Is this a fair understanding of the
idea?

This does not account for labor or deformation, though. Crowned boards would
seem to be more predictable as moisture changes, where an UC board may not
deform uniformly so ultimately courting failure.

All this said, Sohmer and Hallet & Davis weren't Mathushek and I'd venture a
guess that there is/was crown in their boards (let's see - I've got a Sohmer and
a Hallet & Davis at hand, I have thread, bearing guages...).

Clark

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