This is a multi-part message in MIME format. ---------------------- multipart/related attachment ------=_NextPart_001_002C_01C39BCB.E47B5460 Oops! This note was not finished - it was supposed to go to my outbox = for completion later. I deny having anything whatsoever to do with this = post! Terry Farrell ----- Original Message -----=20 From: Farrell=20 To: Pianotech=20 Sent: Sunday, October 26, 2003 9:31 AM Subject: Re: Rib Support Hello Richard. I know some have express some disenchantment with your = persistant theoretical explorations of soundboard crown, but I am rather = enjoying it. It's a good mental excercise. And I also understand that = even though you may well never build a soundboard, it is still a great = thing to try and understand how they might work. There are not very many = authoritative references available to find answers to these questions. So with that in mind, let's proceed to do the best job we can leading = each other into an advanced state of total confusion............=20 Comments interspersed below: Terry Farrell ----- Original Message -----=20 From: Richard Brekne=20 To: Newtonburg=20 Sent: Sunday, October 26, 2003 5:47 AM Subject: Rib Support Hi List=20 I wanted to try and better explain why I am having difficulty in = accepting that the ribs in a CC board do not support crown against down = bearing. Please follow the following reasoning and diagrams and you will = see where I am stumped.=20 First is a panel that is simply bent across the grain and held into = place with a cable appropriately attached on the ends of the panel. = Obviously, when down bearing is applied, the outward pressure on the = cable is increased. This entire situation is going to be the same if one = first dries out the soundboard, then securing that same cable tightly, = let the panel take on enough MC to form the same crown.=20 =20 =20 Replacing the cable with a piece of wood doesn't really change a = whole lot conceptually. The rib will be under the same amount of = tension as the cable was, though the amount of physical strain may = differ. Pressing down on the panel is definitely going to be resisted = by both the panel and the rib. If the assembly is only resting on = supports at the edge, down bearing might even result in some downwards = bending of the rib.. but I will have to try this to see. Still, the = panels edge will <<bend>> in a downwards direction, and there might be = some reaction in similar direction by the ribs. In any case, the = assembly as a whole will resist any down bearing for the same basic = reasons as above.=20 =20 =20 =20 Now if the rib is secured to the panel such that it bends a bit in = the same direction as the panel, (i.e. glue say about 10 inches in on = each side) then the only thing that has really changed is that the rib = bends upwards a bit... as in the below drawing. Yet the same basic = condition exists. Downwards pressure in the panel increases the outwards = pressure, yet this is resisted just in the same way as in the previous = two examples, so in response both panel and rib will feel an increased = stress and will strain against that stress until one of the pieces fail, = which of course will be the panel.=20 Keep in mind here that stress and stain, although related, are two = very different things. Stress is a force that is applied to an object - = or an object's ability to resist deformation. Stain is the deformation. = With the soundboard, I suppose stress is delivered to both panel and = rib, but strain is negligible for the rib, and orders of magnitude = larger for the panel. I've searched for numbers that describe this = relationship, but have found none.=20 But until that point is reached, the entire system will resist down = bearing vigorously. No doubt the rib will straighten at some point, and = the relative tension/compression on the top and bottom sides will = equalize, but it will have to experience an increase in overall tension = for this to happen, which it will resist. The panel will also straight = out at somepoint... but nobody believes for one second that it wont be = under stress when its flat.. So why should the rib be any different ? = Opposite side of the same coin. Both will physically strain against the = stress, the panel a good deal more then the ribs, but the stress levels = are the same on both.=20 =20 The only thing that remains is to simply glue the entire rib to the = soundboard, but I cant see that that changes anything. If the above = three steps hold, then it seems in error to say that the only thing that = supports crown in a CC board is compression in the panel. The entire = system, panel and ribs alike will strain against down bearing.=20 Ok... so this seems to make perfect sense to me, and though ribs are = not acting as beams in their support, they can neither be said to be = purely fighting crown. Quite the opposite. The fact that the rib is bent = in the process, and of course resists this bending can be said about the = soundboard as well. But I dont see that simple bending of either = describes their condition adequately.=20 =20 =20 Cheers=20 RicB=20 --=20 Richard Brekne=20 RPT, N.P.T.F.=20 UiB, Bergen, Norway=20 mailto:rbrekne@broadpark.no=20 http://home.broadpark.no/~rbrekne/ricmain.html=20 http://www.hf.uib.no/grieg/personer/cv_RB.html=20 =20 ------=_NextPart_001_002C_01C39BCB.E47B5460 An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/d1/a2/b9/e3/attachment.htm ------=_NextPart_001_002C_01C39BCB.E47B5460-- ---------------------- multipart/related attachment A non-text attachment was scrubbed... Name: not available Type: image/jpeg Size: 10400 bytes Desc: not available Url : https://www.moypiano.com/ptg/pianotech.php/attachments/97/a7/7c/3c/attachment.jpe ---------------------- multipart/related attachment A non-text attachment was scrubbed... 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