RC vs CC again

[Overs Pianos]

---------------------- multipart/alternative attachment
Ron N wrote:

>Compression crowned is panel supported. Rib crowned can be either 
>rib supported, or a combination of rib and panel supported in any 
>proportion. Rib crowned and supported is just that, with the panel 
>offering little if any support.
>
>Phil Ford wrote;
>>  Why would you categorize a panel that has not been severely dried, 
>>and to which crowned ribs are attached, as primarily panel 
>>supported?
>
>It depends on the dimensions and crown of the ribs, and how do you 
>know what the panel was dried to? If a soundboard is made with 
>crowned ribs that by themselves aren't stiff enough to support 
>string bearing and still retain crown, and the panel wasn't dried 
>down enough to supply bearing support when it rehydrates, then not 
>much of anything is supporting crown against string bearing load. If 
>you are going to have crown remaining under bearing load, it has to 
>come from either the ribs, panel expansion, or both. If the math 
>says the ribs aren't doing it, it pretty much has to be coming from 
>the panel.
>
>For instance, Yamahas are rib crowned, but an analysis of the 
>bearing load the ribs are carrying will show that the ribs can't 
>support the load imposed on them without the panel compression 
>carrying a large percentage of the load. Bending force in the panel 
>cross grain is NEVER significant to crown to my knowledge.  That's 
>why I make the distinction between rib crowned, and rib crowned and 
>supported.
>
>Ron N

Agreed Ron. A couple of further comments regarding RC & S 
construction come to mind. Traditionally, CC boards have been fitted 
with ribs of a uniform sectional area in the body of the panel (ie, 
away from the feathered ends). RC & S construction opens up a whole 
raft of new possibilities since we are no longer relying on the 
forces between the dried-cross-grain panel and the rib set for 
structural strength. When the ribs are crowned to the desired radii 
of the assembled board, without any further assistance from panel 
drying, it becomes possible to contour the depth of the ribs to match 
the board strength to the stress experienced at each given point 
along the length of the rib. While this rib contouring could be 
employed with a CC  design also, I suspect it would be more difficult 
to achieve repeatable results from one case to another. This in 
theory should allow the astute RC & S designer to derive a superior 
board which responds over its entire area in a predictable way. The 
typical CC board is seriously under-engineered directly under the 
bridge, while it becomes progressively over strength as we move away 
from the bridges. This results in a board which is very active 
directly under the bridges (look for the overloaded 
central-long-bridge valley down the centre of many boards - even on 
new pianos, with your 300 mm rule - which will often rock under both 
the long bridge and the bass bridge), with progressively less 
happening as we move away from the bridges. But don't take my word 
for it, build a sample rib or two with panel attached and load them 
up on the bench to see for yourself. I was quite shocked at the test 
bench deflection figures we measured with CC control strips (I was 
also similarly shocked by my first RC proposals when measured under a 
deflection test). In addition to measuring deflection under load at 
the centre of the ribs, we measured their displacement at various 
measurement points along their length. After building many different 
alternatives and measuring their displacement data, it is possible to 
graph the relative displacement activity of one design against 
another.

This is a very interesting topic which can be best understood by 
doing our own experiments and seeing just what happens. This list is 
a wonderful resource, but we must do our time at the bench if we 
really want to gain an understanding of this topic.

I strongly suspect that upholding the CC tradition, just because it 
happens to be the dominant process which has been adopted by a 
dominant manufacturer for the past century, is a sure way to limit 
the possibilities for further evolution of the piano. I'm not simply 
defending RC construction here mind you. I don't care what system of 
construction is used as long as the result is first class from both a 
tonal and reliability perspective. But for progress' sake, let's not 
condemn an alternative approach just because we are unfamiliar with 
it, or because we heard an instrument once that was claimed to have 
been built with such and such method, and in our opinion the piano 
was inferior to something we have in our 'mind's ear'. For example, 
several commercial makers have given laminated panels a nasty 
reputation, but after building instruments with them I am becoming 
more convinced that they have great potential if handled with care - 
but that applies equally to many things.

Ron O.


-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:info@overspianos.com.au
_______________________
---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/54/34/eb/fe/attachment.htm

---------------------- multipart/alternative attachment--