Great old pianos with big, fat ribs........

[Terry]

Assuming you mean me, I don't believe I have ever said any such thing. I
recall that I did mention that two Knabes that I have taken apart had
crowned ribs but that I didn't know if the crown was cut into them or if
they had just warped that way (although my assumption is that the crown was
cut into them). I know nothing about rib designs on Ivers and Pond or
Packard or any Knabe other than the ones I have in my shop.

I believe RC, which stands for Rib Crowned, means that the crowning of the
soundboard is produced by a combination of crowned ribs and panel
compression (the panel is dried down sufficiently prior to ribbing so that
significant panel compression occurs and crown is formed in the soundboard
additional to that formed by the crowned ribs). Downbearing in a RC board is
supported in part by panel compression and part by rib crown. RC&S is Rib
Crowned and Supported - simply meaning that panel compression is
insignificant as a factor in forming crown or supporting downbearing.

Realize that there is much of a continuum between the two. Ron N., Del and I
all dry our panels down to somewhere between 6 and 6.5% MC prior to ribbing.
So even here in panels we describe as being RC&S, there is some panel
compression (although maybe not at the tail end of a really dry spell) and
hence some small amount of support produced by panel compression (at least
when they are new). Perhaps Ron O is the only one that is building a pure
RC&S soundboard with his laminated panels (but even those panels get
compressed a bit when the piano is strung!).

Terry Farrell

> Most of the great old pianos I have, with plenty of
> crown remaining, have very substantial ribs which are
> wider than they are deep. It has been said that an RC
> board should have ribs which are deeper and wide, and
> it has been said ( by Terry ) that thesse old pianos,
> such as mine: Knabe, Ivers and Pond, Packard, ARE RC.
> So why do contemorary RC builders invertthe formula
> which has held these pianos so well? My Packard
> ( free ) has about 10 cracks in the board, but still
> has plenty of crown and sounds like rolling thunder. )
>      Also: My previous question was ignored: "What, in
> terms of construction, is the difference between an RC
> and an RC&S board!
>      Thanks in advance,
>      G
>
>
>
>
> --- Richard Brekne <Richard.Brekne@grieg.uib.no>
> wrote:
>
> > Ah but it is another matter.
> >
> > The RB&S board will by its design nature maintain a
> > more stable
> > stiffness to mass relationship with variances in RH,
> > and the CC board
> > will vary  more across the grain with those same
> > variances.
> >
> > RicB
> >
> > >/  but achieving that and at the same time the same
> > stiffness to mass
> > />/relationships is another matter.
> > /
> > It is not a 'another matter'. If you have determined
> > a certain spring
> > rate but would like more mass you can use more,
> > lower and wider ribs,
> > and your mass will be increased at a given
> > stiffness. If you want
> > less mass for the same stiffness (spring rate) you
> > can use less,
> > deeper and narrower ribs. Its a simple matter to
> > arrive at the spring
> > rate and mass relationship required, using RC
> > construction.
> > Furthermore, I believe that the stiffness of ribs
> > should ideally be
> > varied along their length. The rib should be stiffer
> > under the
> > bridges (where most CC boards collapse in short
> > order), getting
> > gradually weaker as we move from the bridges to the
> > ends of the rib.
> > The tapering of rib strength is a cake walk when
> > building an RC& S
> > board. While the CC building school can contour the
> > panel thickness
> > to increase the stiffness under the bridges, it is
> > more of a 'blunt
> > instrument'.
> >
> >
> > _______________________________________________
> > pianotech list info:
> > https://www.moypiano.com/resources/#archives
> >
>
>
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