<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <META content="MSHTML 6.00.2800.1226" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV> </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">From: <A title=Richard.Brekne@grieg.uib.no href="mailto:Richard.Brekne@grieg.uib.no">Richard Brekne</A> </DIV> <DIV style="FONT: 10pt arial">To: <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">Pianotech</A> </DIV> <DIV style="FONT: 10pt arial">Sent: October 14, 2003 12:47 = PM</DIV> <DIV style="FONT: 10pt arial">Subject: Re: soundboard = stresses</DIV> <DIV> </DIV>  Well just so we are on the same page.... I myself, am not trying to = prove anything with these numbers... except perhaps to prove that I am on = the learning road. I'm in Hoadleys book at a very early stage and am just = pushing numbers around to see if I can the formula usages correct, and in some = basic perspective. I note also that tension strength along the grain is not even given, and is only very lightly refered = too. </BLOCKQUOTE> First, I = mentioned no names. Don't take everything so personally. Second, your = point is?   <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">   <BLOCKQUOTE TYPE="CITE">To complicate things even more, they are based on tests taking a = relatively short period of time -- minutes rather than hours or days. Hoadley, = in his book Understanding Wood, suggests that we must degrade these figures = by approximately 40% if the time under load is going to = be appreciably longer than the time taken for the specific test in = question. This number also appears to be an average as I've had other wood technologists quote degrade figures of 30% to 50% for time under = load periods of five to ten years. It depends, apparently, on the = particular characteristic and the particular species of wood under = consideration. For a characteristic such as tensile strength parallel to grain the = degrade figure can be considerably lower. For a characteristic such as compression = strength perpendicular to grain it will be some = higher.</BLOCKQUOTE> Could you point me to the page and section where this is found ?  Just = for edification really, as for now I have my hands more then full with = getting a handle on  chapters 4,5,6, and 7. </BLOCKQUOTE> Not = specifically. Look for something about time under load or TUL.   <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <BLOCKQUOTE TYPE="CITE">Second, it overlooks the problem that no lumber = grader, regardless of training and experience, can accurately determine any = of these physical characteristics without getting into some form of = destructive testing which, needless to say, is not being done by any piano = manufacturer. Nor has it ever been that I am aware of. At least not in production. = We can't get by with random testing, you see, we would have to test = every single piece of wood.</BLOCKQUOTE> Grin... = that was fast... so.. are you saying that soundboard makers have no tools at = their hands for reliably (say a 90 % confidence factor) selecting materials = that will fall above the average strengths ? </BLOCKQUOTE> Strength and = the ability to withstand compression perpendicular to grain are two different things. And no, there is no such tool that I am aware of. = Which is not to say one couldn't be made if one was interested enough in doing = so.   <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <BLOCKQUOTE TYPE="CITE"> </BLOCKQUOTE> Yes..but !... doesnt that kinda put any soundboard construction at like horible risk ?  And if we reduce Ron's = figures by 50 %.. then it would seem likely that we would be witnessing wholesale = implodic disseminating chaos going on inside of absolutly every CC board within = a few hours after assembly. Or do I misunderstand your point here ? = </BLOCKQUOTE> I don't think = you really misunderstand my point but you do exaggerate. It simply means that = suitable care must be taken to insure the long term stability and integrity of the = thing. Assuming, of course, that such long term stability and integrity are an = issue of concern and that pushing the limits of structural integrity are not a = design feature. Del</BODY></HTML>