<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>Re: Soundboard crown</TITLE> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <STYLE type=text/css>BLOCKQUOTE { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } DL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } UL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } OL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } LI { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } </STYLE> <META content="MSHTML 6.00.2800.1106" name=GENERATOR></HEAD> <BODY bgColor=#ffffff> <DIV><FONT face="Comic Sans MS" color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B> <A title=fordpiano@earthlink.net = href="mailto:fordpiano@earthlink.net">Phillip Ford</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">Pianotech</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> August 17, 2003 1:53 = PM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Soundboard = crown</DIV> <DIV><BR></DIV> <BLOCKQUOTE cite="" type="cite"><BR> <BLOCKQUOTE>----- Original Message -----</BLOCKQUOTE> <BLOCKQUOTE><B>From:</B> <A = href="mailto:Erwinspiano@aol.com">Erwinspiano@aol.com</A></BLOCKQUOTE> <BLOCKQUOTE><B>To:</B> <A = href="mailto:pianotech@ptg.org">pianotech@ptg.org</A></BLOCKQUOTE> <BLOCKQUOTE><B>Sent:</B> August 16, 2003 9:29 AM</BLOCKQUOTE> <BLOCKQUOTE><B>Subject:</B> Re: Soundboard crown</BLOCKQUOTE> <BLOCKQUOTE><BR></BLOCKQUOTE> <BLOCKQUOTE><FONT face="Times New Roman" = color=#000040><BR>>>Phil-- My thought was that any wood will shrink over time especially = quartered wood because of it's expansion contraction properties and actually = that could take some time. </FONT></BLOCKQUOTE></BLOCKQUOTE> <BLOCKQUOTE cite="" type="cite"><FONT face="Comic Sans MS" color=#000080>Wood does not shrink on its own--at least not so you = would notice--only as a result of changing environmental conditions, i.e., = with changes in the MC of the wood. Kept in an temperature/humidity = stable environment what would cause it to shrink?</FONT></BLOCKQUOTE><FONT face="Comic Sans MS" color=#000080></FONT> <DIV><BR>I was thinking that normal seasonal variations in humidity = would cause it to shrink.</DIV></BLOCKQUOTE> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>I was = refering to the first comment, above. The reduction in panel width that takes place = because of compression set is not technically shrikage. It is a reduction in size = resulting from compression damage to the wood cells. </FONT><BR></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <BLOCKQUOTE cite="" type="cite"><FONT face="Comic Sans MS" = color=#000080>I assume you're referring to the (so far, unsubstantiated) phenomena = of "oil-canning."</FONT></BLOCKQUOTE> <DIV><BR></DIV> <DIV>I don't think I was.  But I'm not really sure what that = is.  Can you explain what you mean by this?</DIV></BLOCKQUOTE> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>The effect = noted when depressing the bottom of an oil can. Initially it is bowed out slightly. = By pressing on it it pops in to approximately the same radius in the = reverse despensing a more-or-less precise amount of oil in the = process.</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV><FONT face="Comic Sans MS" color=#000080></FONT> </DIV> <DIV>I wasn't really referring to a compression crowned board.  I = think the configuration that I have in mind would be uncrowned or reverse = rib crowned, if that makes sense.  I wasn't thinking of a CC board = that had collapsed.  I was thinking more of a board that was made = deliberately made to have a reverse crown, such as some of the pianos that Dale has = seen (assuming they were intended to have reverse crown).  So, take an = undried panel, glue on some ribs, and load it up.  It will reverse crown = and the board will be in tension I think.  Or machine crown some ribs to = give the board a reverse crown when they are glued on.  Load it up and = once again I think the board will be in tension.  Now if this board is = subjected to a drier environment that that at which is was glued up what will = happen?  I was assuming that the board would take on additional tension.  = Enough to overload it?  I don't know.  But if not, then when this = board is subjected to more humid environments than that at which it was glued = up it would probably be less likely to sustain compression damage than a CC = board, or even a rib crowned board with positive crown.</DIV></BLOCKQUOTE> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>Yes, I see = what you mean. I don't see how, in anything remotely resembling average climate = conditions, you would generate enough tension to cause the thing to crack. Assuming the = panel was at some MC in the 7% to 9% range when it was ribbed.</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>I still = think, however, if the board were taken down to typical compression-crowning MC levels = before ribbing the effect of the developing stress interface would work to = force the board into a positive crown. </FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>The = propensity of any soundboard to develop cracks depends on its MC when glued to the ribs. = If a panel is glued up at 3.8% to 4.0% MC even in a reverse crown = configuration it is going to develop significant compression as it takes on moisture. How = could it avoid doing so? It is the extremely low initial MC and the act of gluing = the thing to those perpendicular-to-grain ribs that creates the problem.</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>It will be = interesting to read about the results of your experiment, however. When will you be finished?</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV>I was also speculating about what would happen to this board if = it was subjected to a drier or more humid environment.  My thought was = that in a drier environment the board would want to move up.  My thought = was that the board is describing an arc.  As it dried this arc would have = to get shorter, so the board would want to flatten out, which in this case = would mean moving up.  You seem to think it would move down.  Why do = you think that?</DIV></BLOCKQUOTE> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>Good = question. You'll have two forces fighting each other, but they'll not be equal forces. I think = the stress interface will win. At least until the panel = self-destructs.</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>I think the = shrinking panel will crack before it creates enough lifting force via tension to accomplish anything and the stress interface will pull it down. As well, = </FONT><FONT face="Comic Sans MS" color=#000080>I think an expanding = panel will work against itself but the stress interface will create the enough = force to push the ribs up no matter how those ribs are initially crowned. If = the ribs are machined with a reverse crown and glued to a panel with very = low MC, the expanding panel will still want to force the assembly positive. It = may not make it but it will sure try.</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>Will this be = part of your experiment?</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px"> <DIV><FONT face="Times New Roman" color=#000040>With a = conventional board having crown and with a downbearing load I think the board is always = in compression....  </FONT><BR><FONT face="Times New Roman" color=#000040></FONT></DIV></BLOCKQUOTE> <BLOCKQUOTE cite="" type="cite"><FONT face="Comic Sans MS" = color=#000080>I am uncertain what is meant by "a conventional board." Assuming this = refers to a compression-crowned soundboard system, the key words in the = above are then "having crown." However, a strong argument can be made that = this is no longer--if it ever was--the conventional soundboard system....</FONT></BLOCKQUOTE> <DIV><FONT face="Comic Sans MS" color=#000080></FONT><FONT face="Comic Sans MS" color=#000080></FONT><FONT face="Comic Sans = MS" color=#000080></FONT><FONT face="Comic Sans MS" = color=#000080></FONT><FONT face="Comic Sans MS" color=#000080></FONT><FONT face="Comic Sans = MS" color=#000080></FONT><BR></DIV> <DIV>I wasn't intending to comment on CC vs RC boards here.  By conventional, I meant a board that was intended to to have a positive = crown, which includes every piano I've ever seen (but not every piano that = Dale's ever seen).  I therefore felt safe in calling this 'conventional'.</DIV></BLOCKQUOTE> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>Ah, but that = doesn't correlate to the first statement above which states, "With a = conventional board having crown and with a downbearing load I think the board is always in compression." This is the comment I was responding to and wondering just = what was meant by "conventional." Over the decades I suspect far more pianos = have been built with either hybrid systems (probably the most common) or = rib-crowned system than have been built using compression-crowned systems. And both = the hybrid and the pure, or nearly pure, rib crowned board will have = crown even without any compression in the panel. Our panels are ribbed at 6.5% MC. = When atmospheric conditions are such that the panel is at 6.5% MC there is no = internal compression within the panel. Yet there is design crown. Over = the years if these boards are subjected to very high levels of humidity (and the corresponding high MC) they will also undergo some amount of compression = set. Still, there will be crown when they return to equilibrium at = whatever MC that may end up being.</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV> I was pondering a what if scenario.  What if you built = a board that was intended to have a reverse crown.  How would it = behave?  Would it have any advantages over a 'conventional' board that is = intended to have positive crown?</DIV> <DIV><FONT face="Times New Roman" = color=#000040></FONT> </DIV> <BLOCKQUOTE cite="" type="cite"><FONT face="Comic Sans MS" = color=#000080>As well, it is quite possible to have a string downbearing load without = having positive crown.</FONT></BLOCKQUOTE> <BLOCKQUOTE cite="" type="cite"><FONT face="Times New Roman" color=#000040></FONT> </BLOCKQUOTE> <DIV>Yes, I know.  But in this case it would be a deliberate = design feature rather than an unintended consequence.</DIV></BLOCKQUOTE> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>Well, there = is always the Rippen--the only modern piano I know of built deliberately to have = reverse crown. Actually, the (laminated) boards were ribbed flat and, when = loaded with string bearing, were forced to a reverse crown. They worked. At least = within the limitations of their less than desirable scaling. As to whether they = might have worked better with some form of positive crown, I have no idea. Nor do I = have any idea how they would have worked had their panels been made of solid stock.</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>Del </FONT></DIV></BODY></HTML>