>> CC=compression crowned, consisting of flat ribs with panel compression >> forming and supporting crown under both string downbearing and the >> ribs' attempt to naturally straighten back out. Steinway US, >> Steingraeber, and Sauter build boards this way. > > And yet Hartwig of Steinway Hamburg is reported to say "and yes the ribs > are slightly curved prior to gluing them onto the board." Depending on > what he means by "slightly", surely that could mean a Steinway board is > more or less "rib-crowned" by your terminology? I said Steinway US, as in NY. They have always used flat ribs, and by all indication always will. The Hamburg product is considerably different. An eternal source of confusion also comes from the always vague wording concerning "curved" ribs. If the curve is cut into the rib, yes, it's rib crowned. If the curve is bent into the rib, no, it's compression crowned. Which is the case here? >> RC=rib crowned, consisting of ribs with a crown machined directly into >> them,.. > > Would that be the same,in effect, as saying planed to a convex curve on > the upper side? Correct. >> ..and supplying positive beam support to crown under downbearing in >> addition to the support supplied by panel compression. > > This compression being created by the force produced by the summer > growth (mainly) of the spruce trying to expand after being glued to the > ribs in a more or less dehydrated condition. Is that what you're > saying? It seems to be, but anyone reading your description without > much knowledge might easily ask "what compression?!" Yes. Panel compression is also commonly achieved or increased by pressing the assembly into a curved caul as the ribs are glued on. >> This is the most common construction method among today's manufacturers. > > And has been a common construction method for well over 120 years, is > that not so? Yes, it has. >> RC&S=rib crowned and supported, consisting of ribs with a crown >> machined directly into them, sized and numbered sufficiently to >> support crown under downbearing load without the aid of panel >> compression. To my knowledge, Walter is the only manufacturer building >> boards this way, though there are a number of small shops doing this >> now, with considerable success. > > Do you count yourself among that number? Yes. My crowned rib sets would support full string downbearing without the panel being present. >If I understand this correctly > in the context of the other two methods and by contrast with them, then > when the board is glued to the ribs, presumably without any previous > special dehydration, the curvature resulting in the board will lead to > some tension in the board and when the piano is strung and the curvature > of the board diminishes this tension will diminish and leave the board > in roughly a state unstressed either by tension or by compression. Is > that, broadly speaking, the intention? I dry panels to 6%MC, so depending on where the piano goes, there will often be some compression in the panel. The difference is that the RC&S assembly doesn't need panel compression to maintain stiffness and crown under bearing load, where the CC and RC do. Ron N
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