Ron Nossaman wrote: > But Steinway doesn't chose the dry-down MC based on where the pianos > will end up, do they? They take a panel that was at whatever they use > for a dry standard (4.5%?, 4%?) out into a room with the windows open > and 80%+RH air blowing through to set the bearing, regardless of where > it will eventually end up. Is that not the case? The soundboards have > gone from 4.5%MC to over 14%MC before they even get out of the factory. I am not endorsing a particular method. I certainly am not thinking that Steinway has it right. I mite as well not be in business if I thought that. But I am not inclines to take a jab at them every chance I get. I was just pointing out that one should take into consideration the environment that the piano is living in to set the moisture content at the time of ribbing. Dale says he uses 5.5 to 6% because his environment is on the dry side while I here in the north east find that 6.5% is best. > Yes, the starting point is important, but how can you build a flat > ribbed CC board by drying it down to only 6%MC when you can't have any > idea how dry it will be at it's final destination? Well you can if the cauls are deep enough. None of us know for sure how dry it will be at it's final destination. We already talked about the 30% RH window. It applies to all soundboards. > > But it does. It supports the entire bearing load, as well as bending the > rib. We're talking about different things, or at least the same thing at > different points in the assembly process. Granted, it's not double what > it takes to bend the rib into a crown in the first place because as you > add bearing, the rib straightens and provides less resistance to crown. > So you're right that the load increase doesn't all that significantly > increase the panel load, but only because the crown is pressed down. The > panel trades some of the diminishing rib load for the increasing bearing > load. Ok, I got it. This is during assembly and stringing, where the > crown initially formed by the panel compression bears little resemblance > to the crown it becomes under string bearing load. After final assembly, > the panel compression is the result of the sum of the force required to > keep the rib bent and support the bearing load - at a given final crown > height. That's what I'm talking about. The fact remains that the panel > is still supporting both the rib and the bearing as long as any crown > and bearing remain. I am willing to consider this as true. But I still say that if the panel does not exceed its elastic limit the stiffness of a PC board will be the same as the stiffness of a RC board as long as the ribs are the same dimension. My argument has been against the notion that the method of crowning a soundboard has a direct effect on its stiffness. Panel crowning's chief weakness is that the soundboard must be kept within a narrow range of RH. But if it is kept in that range its performance acoustically and mechanically should not be any different than a similar rib crowned board. I have been getting the impression from some of the posts on this topic that it was understood that a PC board would just instantly fall apart. The poor week panel holding everything up. I think that that is a an exaggerated claim clearly aimed at embarrassing the manufacturers and rebuilders using this technique. Maybe I have this wrong but this strikes me as an impediment to studying how these things work. John Hartman RPT John Hartman Pianos [link redacted at request of site owner - Jul 25, 2015] Rebuilding Steinway and Mason & Hamlin Grand Pianos Since 1979 Piano Technicians Journal Journal Illustrator/Contributing Editor [link redacted at request of site owner - Jul 25, 2015]
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