Only mildly related here, but does anyone know if Steinway made any changes to their crowning procedures as a result of the lawsuits filed by A. Michael's Piano Co. some 15 - 20 years ago? Whatever you think of his methods, he did cause quite a stir. Lots of pictures of compression ridges, cracks, loosed ribs -- and this on pianos still in the showroom. Did Steinway make any procedural changes after this? Does anyone else remember all this? dave __________________________________________ David M. Porritt, RPT Meadows School of the Arts Southern Methodist University Dallas, TX 75275 ----- Original message ----------------------------------------> From: Ron Nossaman <RNossaman@cox.net> To: Pianotech <pianotech@ptg.org> Received: Mon, 13 Oct 2003 12:31:29 -0500 Subject: Re: soundboard stresses >>O.K. Ron. So you are saying that a cross grain spruce reacts to stress in >>a non linear way. It resists compression more and more as it is >>compressed? As I see it, with my limited understanding, it should react to >>compression forces in a linear and predictable fashion within the elastic >>range. Check out a stress strain graph to see what I mean. >Yes, John, I see what you mean. So let's go with that. Looking at the >stress/strain chart in Hoadley's "Understanding Wood", I also note that the >elastic limit is less than 1%, which is also stated in the text. Using the >supplied formula with the appropriate expansion/shrinkage average for Sitka >spruce, we get >Dimensional change = Lin*0.043*((MC%2-MC%1)/0.28) >with MC%1 being the lower MC and MC%2 the higher. >We see that a panel that is 36" wide at 4.5%MC will expand by 0.359" when >taken to 11%MC. It's proportional, so any width will produce the same >percentage size change (1% with these MC ranges). That will happen at 70° >@ 60% relative humidity. Constraining this panel to a flat rib will bring >it under compression beyond the fiber stress proportional limit, indicated >in this same reference at 580psi radially perpendicular to the long grain, >and induce some degree of immediate and permanent compression set. I submit >that it is highly unlikely for a piano built this way to remain under 11%MC >forever to avoid immediate panel damage, never mind long term compression >set which occurs at a rate proportional to internal compression. I also >submit that it is highly likely that the piano will reach an MC >significantly above 11% before it even gets out of the factory, so >permanent panel compression damage almost certainly occurs before the piano >is even finished. >Note that this is irregardless of the ribbing material used, bearing, or >panel thickness, and is merely the result of assembling a compression >crowned panel with flat ribs. >This looks to me to entirely contradict your claim that building CC boards >with flat ribs does not put the panel at damagingly high compression >levels. Immediate compression damage seems to, instead, be a realistically >unavoidable consequence. >Incidentally, I had always heard 4%MC quoted as the preferred dry down >level for this type of construction. When did it become 4.5%, and why? >Ron N >_______________________________________________ >pianotech list info: https://www.moypiano.com/resources/#archives
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