This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment ----- Original Message -----=20 From: Richard Brekne=20 To: Pianotech=20 Sent: October 02, 2003 12:28 PM Subject: Re: RC vs CC again =20 Delwin D Fandrich wrote:=20 =20 Grin... now THATS what I'm talking about !!... Seriously tho... this = is easy enough to follow. Do you have a similiar formula for how much = stiffness the assembly takes on for panel compression ?.. =20 I do not know of any way to predict the panel stiffness of a = compression-crowned soundboard system. Even if a formula were developed = I suspect the many variables would degrade accuracy to the point of = uselessness. And.... well.. you could always increase height of the ribs in a CC = board as well... but then... that wouldnt make much difference given = that the ribs dont do a lot to support the pannel.=20 Well, think about this a bit. What would be the effect of a tall rib? Of = course it would make a difference. It would limit the development of = crown and further increase the amount of compression within the panel. So.. what.... the ribs function in a CC board is primarilly to force = the panel into compression ?? Why the choice of fat and not so high = instead of lots of height... or something else... what determines your = choice of rib dimensions in a CC board ?=20 Since I no longer do them I don't have to make that choice.=20 As to why they are wider than they are tall (and I've now written this = so often my fingers can find their own way around the keyboard with no = further input from my brain -- so repeat after me....) THE RIBS IN A COMPRESSION-CROWNED SOUNDBOARD SYSTEM HAVE TO BE FLEXIBLE = ENOUGH TO BEND IN RESPONSE TO THE STRESS INTERFACE BUILT UP BETWEEN THE = EXPANDING SOUNDBOARD PANEL AND THE RIBS. THIS IS HOW CROWN IS FORMED IN = THE COMPRESSION-CROWNED SOUNDBOARD SYSTEM. If the ribs are too stiff there will be little or no crown. The wood = fibers will still compress as they take on moisture but they won't be = able to develop enough force to create a crown in the system -- the = wood's perpendicular-to-grain compression strength limit will be = exceeded before crown is developed. Selecting the right rib = cross-section was probably an empirical study in cause and effect. Del ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/ce/a9/8e/3a/attachment.htm ---------------------- multipart/alternative attachment--
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