laminated ribs

[William R. Monroe]

Terry,

How do you get the bathroom scale at the exact height of the top of the
bridge?  Do you just place it on the board near the bridge and try and shim
it to approximate that height?  Have you experimented to find how much
difference in force there is with variations in height?  Do you know if
there may be any significant flex in either the upper go bar deck as you add
more bars, reducing the force on the previous bars, or if the deflection of
the soundboard as you add bars is enough to reduce force appreciably on
previously installed bars?

Not nitpicking here, just very interested in the subject, particularly how
much error is tolerable in these things.

Regards,
William R. Monroe



----- Original Message ----- 
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: "Pianotech List" <pianotech@ptg.org>
Sent: Sunday, February 19, 2006 6:42 PM
Subject: Re: laminated ribs


David M. Porritt wrote:

While you have an unstrung board is it possible to put weights on the bridge
approximating the downbearing load you expect to have then reexamine the
crown and bearing angles?  Would this give an elementary idea of the board's
ability to sustain that load?

Yes indeed. I consider that to be an integral step to setting up a new
soundboard. I use go-bars to apply down-force to the bridges (see the
picture below). I calibrate the go-bars by measuring the go-bar pressure
with a scale (see second picture - my wife keeps bugging me: "Terry, where
is the bathroom scale?"). I suspect that after one has built and set up
many, many soundboards, this step may not be necessary. But I find a
tremendous educational dimension to the process.

Terry Farrell