I see. By larger piano do you mean a D? Or are you going up to 900 lbs for, say, a B as well? You mentioned previously that you are building the ribs for higher load than you started originally and you found that there was some relationship to hammer tolerance. The boards that you are now building that are set up for, say, 650 lbs, what would those have been previously? Just as an aside, you said that you plan for 40% deflection and end up somewhere between 40 and 50%. I assume you are calculating your deflection from beam formulas and basing it on the rib properties only and ignoring the panel in the calculations, for the most part. It's interesting that when you calculate for deflection based on the ribs only that the panel itself contributes very little if anything to the stiffness of the assembly in terms of the overall deflection. Do I understand that correctly? David Love davidlovepianos at comcast.net -----Original Message----- From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Ron Nossaman Sent: Saturday, March 25, 2006 8:22 AM To: Pianotech List Subject: Re: laminated ribs > Ron: > > I just want to revisit this for a moment. Do you mean your typical load is > 900lbs? And if so, what kind of deflection are you building your ribs for, > i.e. what percentage of the original crown do you figure is remaining after > the board is loaded? > > David Love David, Somewhere in the vicinity of 900, in a big piano. I'm figuring 1° in the bass, up to something between 1.5° and 2° at the top. I calculate for about 40% deflection in design, and wind up between 40% and 50% in reality. I'm happy with at least 50% of the original crown remaining. A smaller piano with fewer ribs might get more like 600 or 700 lbs, with bearing angles adjusted accordingly. Since the spring rate of rib supported boards is much more nearly linear than in panel supported boards, small changes in bearing angles don't have dramatic effects on tone, so the whole thing becomes more structurally and less tonally oriented. Ron N
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