>Ron, >I wouldn't think that most cutoff bars that I have >seen would add much support to the rim. Do you >also modify the design of your cutoff bars to make >them heavier? No, most of them don't. Mine do. They do tend to be heavier than what you see in most pianos, and considerably more of the bass corner is cut off than is the case in most pianos. Look at that sketch Del posted when we were talking about fanned ribs. Imagine a similar bar made out of straight pieces, the longest going from belly rail to rim, with a branch or two going from the first bar to the rim to continue the approximate curve around in steps, rather than in one continuous curve. You will have what amounts to two diagonal braces to the side and a very stiff cutoff bar. Where the bar crosses an existing beam, it is glued and doweled to it. >Why do you use softwood for the bracing? Also, do >you have any thoughts about why most makers seem >to use softwood for the bracing rather than >hardwood? > >Phil F Most of what I re-engineer doesn't have a maple belly rail in the first place. The maximum compression parallel to the grain in hard maple is about 7830psi, while for yellow poplar, it's about 5540psi. Maximum compression perpendicular to the grain in hard maple is about 1470psi, while for yellow poplar, it's about 500psi. The modulus of elasticity of maple is about 1.83 million psi, where for the poplar, it's about 1.58 million psi. Under the circumstances, I haven't seen much potential benefit to bracing a belly rail with a 500psi crush point with a brace with a 7830psi crush point. With a maple belly rail, I might use maple, but I'm not that sure there would be any discernable advantage over using poplar. Any bracing at that point helps. Ron N
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