Strips or wedges

[Michael Jorgensen]

Plate brace compression? Really?  When I'm tuning with the RCT using the
same tuning file as last time, where the piano has gone slightly flat,
I'm finding that the pitch is most flat next to the braces, and changed
little in the areas between. This runs counter to the test results given
below! (unless pitch raising/lowering arouses a different reaction than
normal tuning change over time and weather change does.)  This leads me
to suspect it's the empty spot on the bridge causing the change. Typical
change from six weeks ago--  Dead on in the middle of sections 2-3 cents
flat next to braces, and ofcourse drasticly off at bass break.)
Bridgemakers!, What is the proper term for that empty spot at section
breaks?

-Mike Jorgensen RPT --who tunes all CMU pianos every six to eight weeks.


 Richard Moody wrote:
> 
> ----------
> > From: Newton Hunt <nhunt@jagat.com>
> > To: pianotech@ptg.org
> > Subject: Re: Strips or wedges
> > Date: Monday, November 02, 1998 3:46 PM
> >
> > Dmsaerts@AOL.COM wrote:
> >
> > > Mr Coleman  wrote:
> > >
> > > "I don't have the data, but I do remember the graph of the pitch drop
> after
> > >    a pitch raise. The graph showed scallops between the struts. In
> other words
> > >    the pitch dropped more between the struts than it did at the
> struts. This
> > >    indicates that the plate web flexes, but less where there is the
> support
> > >    of the struts."
> > >
> > > The reason could be that there is more space between unisons at the
> struts.
> > >
> > > Cyrillus
> >
> > No, it is because the struts compress less than the webbing.
> >
> >                                 Newton
> 
> If the metal plate is "compressing" due to tension, it should be able to
> be measured. How much  are we talking here?  The plate is supposed to be
> rigid.  FWIW if the speaking length of a 20 inch string at A440 is
> shortened by .02 " the resulting freq is 440.4404.
>         On the other hand, it is conceivable that a space on the bridge could
> exert a little more force where there is a gap in the strings, but I
> wouldn't know where to begin to figure that one.
>         If a string is removed a dramatic sharpening of the adjacent strings
> occurs, but that I don't think has anything to do with the space on a
> bridge running under plate struts. Now if the bridge behaved like a wet
> noodle in supporting the strings. . . . ..........I guess by some stretch
> of the imagination one could find support for Cyrillus's premise...
> 
> Ric jus noodlin'