This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment Comments below: Terry Farrell =20 ----- Original Message -----=20 From: "Delwin D. Fandrich" <pianobuilders@olynet.com> > I was debating with myself as to whether or not I should warn you = about > this, ultimately deciding that experience is a really great teacher = and you > weren't jeopardizing any priceless pianos on your road to discovery. = You can > use a spruce panel as a humidity indicator but you have to allow it to > free-float. I.e., you cannot allow it to come under compression. Gee whizz. Nice guy! It was a very good educational experience. Now how = can you free-float a gauge? The only way I can imagine that is to not = put a rib on it, and simply measure the change in length across the = grain. Is that what you have in mind? =20 > Yes, what you are witnessing is 'compression set.' This phenomenon = takes > place any time wood cells are placed under compression and are = particularly > observable when the compression is applied perpendicular to grain. It = is > difficult for people who have a nearly religious belief in viability = of the > compression-crowned soundboard to understand just how devastating > compression set can be to the stability of the completed soundboard = panel. > Or how quickly compression set can occur. Your little experiment = graphically > illustrates both the speed and extent to which compression set can = occur. I be a believer! I be seen it with my own eyes! This quickly brings to my mind the sight of several semis full of = (compression-crowned-type) new pianos for a local "University Sale" that = sat for a week in a blacktop parking lot in Tampa Florida in the full = sun during the hot monsoon month of July. Not a pretty thought. Is it possible this had anything to do with the negative 1/4" of crown = in MY new "famous NY manufacturer" piano? "Ideally, your S%$#*&y piano should reside in a temperate atmosphere = where relative humidity ranges from 45% to 65%. Don't position it in the = path of an air conditioning outlet or a heating outlet. Don't put it = near an evaporator cooler or a room humidifier. Don't put it close to an = uninsulated outside wall. .....the instrument subjected to such = environmental insult may be permanently damaged." Again, I be a believer! I be seen it with my own eyes! > Actually, compression set follows a log curve. If you place a sample = under a > given amount of compression, compression set starts to deform the wood > fibers immediately. This, of course, reduces the amount of compression > (pressure on the fibers) and the rate of compression set decreases. > Ultimately, the pressure against the wood cells will deform them to = such an > extent that further compression set is reduced to virtually (though = not > exactly) nothing. So, like, check the weather report before you have the movers put your = piano in their truck - pick a good humidity day! =20 > Keeping a piano with a compression-crowned soundboard in a = hermetically > sealed environment would not relieve the problem unless the atmosphere = in > the hermetically sealed environment were maintained at such a level as = to > keep the soundboard panel at 4% MC. Does a semi in an August Florida monsoon meet this criteria? > In this environment, of course, the > soundboard assembly would not have any crown. The problem of = compression set > is present any time a panel such as a spruce soundboard panel is = placed > under perpendicular-to-grain compression and this occurs immediately = upon > returning the newly-ribbed soundboard assembly to normal atmosphere. = It is > only exacerbated by installing a bridge, gluing the assembly into a = piano > and loading it with some amount of string bearing. Ouch! Hurts just thinking about it. =20 > Del =20 > ----- Original Message ----- > From: "Farrell" <mfarrel2@tampabay.rr.com> > To: "Pianotech" <pianotech@ptg.org> > Sent: Wednesday, April 09, 2003 7:00 PM > Subject: Re: Soundboard Torture - and Failure! > > > > My gauge has been in the shop now for a week at 45% RH. It did not = settle > back at the two/three-inch crown position. It is nearly straight, with = only > about ONE INCH of crown. I thought that because the ribs are so thin = it > would bend quite a bit (which it did) at high humidity, but not crush = the > spruce panel. Apparently, the panel suffered quite a bit a damage > (compression set I suppose) with just the one several day exposure to = high > humidity. Just imagine what that would do to a piano soundboard that = has > one-inch by one-inch ribs and all the strings only allowing it to = expand a > tiny bit. CRUSH, CRUSH, CRUSH! > > > > I'm getting the to the point where I think a good piano should spent = its > life with museum-like environmental control - nothing less will do. ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/6d/b7/02/4c/attachment.htm ---------------------- multipart/alternative attachment--
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