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

[gordon stelter]

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'.
> 
> 
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> 


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