---------------------- multipart/alternative attachment Ok.. Thanks muchly for your patience once again. This has been very instructive. I think I am pretty clear on what I was asking about. It will be easier reading the two texts at this point, knowing better what I am after. Cheers RicB Delwin D Fandrich wrote: > > > ----- Original Message ----- > From: Richard Brekne > To: Pianotech > Sent: August 29, 2003 1:57 PM > Subject: Re: Compression Question > A few days back you said > > "If the degree of compression is beyond what the > wood can handle--i.e., it is stressed beyond its > proportional limit--the wood fibers will crush > immediately. If it is compression stressed below > its proportional limit compression-set will work > to reduce that compression stress slowly over some > period of time. In both cases there will be forces > at work to reduce compression, in the first > situation it simply happens faster." > > So.. given what you say above, am I to understand that a rib > crowned board ribbed when the panel is about 6.5 - 7 % MC > will not suffer enough compression set during its > lifetime... say 30 - 50 years , to cause any real > compression / compression related problems ? > > No. Some compression set will occur any time the MC of the panel goes > substantially above the MC at which the panel was ribbed. It is a > matter of how much compression set can reasonably be expected to > occur. In a perfect world the amount of compression set will be > reduced to a level that will not seriously impair the wood's tensile > strength at the lowest MC that it will be reasonably expected to > survive. In the real world the possibility still exists that the wood > fibers might be damaged to some extent but the chances this happening > to an extent that will result in visible damage to the panel have been > reduced considerably. In addition, if the soundboard's rib system has > been properly designed any cosmetic damage that does appear will be > just that--cosmetic. Crown and stiffness are born by the rib system > not compression within the panel. I could deliberately cut slots > periodically across the surface of the panel (longitudinally with the > grain) through to, but not into, the ribs and it would not affect the > acoustic performance of the system. (Except, of course, for some > acoustical coupling between the top and bottom surfaces.) And, indeed, > this has been done. By Vose, I think. In other words the panel is now > functioning almost completely as a radiating surface, not as a > load-carrying structural member. > > Del -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway mailto:rbrekne@broadpark.no http://home.broadpark.no/~rbrekne/ricmain.html http://www.hf.uib.no/grieg/personer/cv_RB.html ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/15/d4/49/32/attachment.htm ---------------------- multipart/alternative attachment--
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