---------------------- multipart/mixed attachment Is, then, the general consensus that stiffening the belly rail may help some in tone production but will not assist in maintaining crown? That seems to be what I'm getting here with my severely diminished mental capacities of late. Corrections? Greg Newell At 11:50 PM 4/10/2003, you wrote: >> I know that someone has done the math on this. How much "spread" is >>required of a rib that is 20 inches long, curved on a radius of say 40' to >>allow the center to drop .020"??? It has been too long since I dragged my >>kids through high school geometry to remember arc and such, but I know >>somebody out there has the answer at hand. > >>A 20" rib with a 40' crown radius has a crown height of 0.104". The >>measurement across the top of the rib, along the curve is about 20.0015", >>or just about 1.5 thousandths of an inch difference. Roughly half the >>diameter of a human hair. >> >>A 36" rib with a 40' radius crown has a crown height of 0.338, and a rib >>length to arc length difference of 0.008. > >Sorry, I forgot something... >A rib 20" long will typically be carrying string bearing loads of somewhat >over 40 pounds total. With a 40 foot radius crown, and a 40 pound load, >the thrust against the rim would be around 1,920 pounds. That's just for >one rib, not counting the other twelve or so. A 13" rib, for instance will >be carrying around 90 pounds, with an outward thrust of 6,640+ pounds. I >know I can't build a wooden piano rim that would hold anywhere near that >kind of force with under 0.0015" deflection (0.0004" for the 13" rib). > >Ron N > >_______________________________________________ >pianotech list info: https://www.moypiano.com/resources/#archives > Greg Newell mailto:gnewell@ameritech.net ---------------------- multipart/mixed attachment--
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