<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> <title></title> </head> <body> Delwin D Fandrich wrote: <blockquote cite="midNCBBLPIFHEMDJHENPLOAAENICHAA.fandrich@pianobuilders.com" type="cite"> <blockquote type="cite"> <pre wrap="">The more I hear this "the ribs are doing nothing but trying to straighten out the panel" the less it makes sense. Ok so the ribs are bent as part of the crowning process... so is the panel.. but nobody talks about the panel trying to staighten out ribs... yet you could just as well turn the whole "lets blame the panels expansion" argumentation on the ribs. </pre> </blockquote> <pre wrap=""> Now, wait a minute here. Who said "the ribs are doing nothing but trying to straighten out the panel."? With or without crown, and regardless of how crown is obtained, the ribs are going to add stiffness to the assembly. That does not preclude their resisting being bent in the compression-crowned soundboard assembly. </pre> </blockquote> You guys do !  And quite frequently. Ok...in the context of rib supporting crown. But forgive me... I am a bit foggy on how it is that ribs that in that context do nothing but resist crown and offer no support against downbearing, can at the same time not only make the panel stiffer (which makes it harder to press down.. hmmmm ) and not only that but makes the system increasingly stiffer (even harder to press down) as more downbearing is applied. I am just sure I am crossing Z's with Ø's here... but these two positions seem a bit contridictorary to me. <blockquote cite="midNCBBLPIFHEMDJHENPLOAAENICHAA.fandrich@pianobuilders.com" type="cite"> <pre wrap="">No one talks about "the panel trying to straighten out the ribs" because it doesn't work that way. Have you ever handled an edge-glued spruce panel? Sure you have. Just how much straightening is that thing going to do? </pre> </blockquote> What I see is two pieces of wood that are forced into a curved condition against their better judgement... and both... would return to being flat if they had their ditthers about it.  Why would the rib be pulling on the panel to straighten it out, and not the other way around in equal amounts ? <blockquote cite="midNCBBLPIFHEMDJHENPLOAAENICHAA.fandrich@pianobuilders.com" type="cite"> <pre wrap=""></pre> <blockquote type="cite"> <pre wrap="">I would suggest that the ribs are not bent simply because the panel is taking on moisture... but because they are made to resist any panel expansion at the interface between ribs and panel. It seems only half a truth and one that easily leads to less then half truths to simply say the ribs are bent by the panel, and do nothing more then resist crown. </pre> </blockquote> <pre wrap=""> I think you're getting the idea. In the compression-crowned soundboard assembly, the ribs are indeed bent because of the stress interface between them -- they really don't like to stretch along their grain -- and the expanding soundboard panel. (At least the panel would be expanding if it were not constrained by the ribs glued to it.) And the panel is expanding because it is taking on moisture. That is how a compression-crowned soundboard assembly works. </pre> </blockquote> Well heck there Del... this much has been clear all along... and of course we dont want the ribs to actually strain along the grain... but that doenst mean they dont feel the increase in stress in that direction. If they strained or failed... then crown would disapear as well. <blockquote cite="midNCBBLPIFHEMDJHENPLOAAENICHAA.fandrich@pianobuilders.com" type="cite"> <pre wrap="">Again, who said the ribs do "nothing more than resist crown?" </pre> <blockquote type="cite"> <pre wrap="">No doubt the bend in both panel and rib seen as isolated component forces will exert a force that works against crown. Funny how tho the net effect is plenty of crown and plenty strength. </pre> </blockquote> <pre wrap=""> Yes, it is, isn't it? Until, of course, either the glue joint fails or compression set within the panel reduces the stress interface between the panel and the ribs to the point the system is no longer able to support crown. </pre> <blockquote type="cite"> <pre wrap="">Also.... this thread has hinted at a difference between the CC panel and RC panel yet to be brought to light... one that has quite probably significant performance ramifications. This matter of increased stiffness when downbearing is applied to the one, vs constant stiffness for the other. </pre> </blockquote> <pre wrap=""> It remains to be seen whether the effect holds true for both types. Until I actually try it I'll hold my further comment. It also remains to be seen just how much affect this characteristic may or may not have on the two different types of soundboard configurations. Del _______________________________________________ pianotech list info: <a class="moz-txt-link-freetext" href="https://www.moypiano.com/resources/#archives">https://www.moypiano.com/resources/#archives</a> </pre> </blockquote> </body> </html>