<table cellspacing="0" cellpadding="0" border="0"><tr><td valign="top" style="font: inherit;"><div>As I sit in awe of this discussion (barely comprehending half of it!) I feel nevertheless inspired to inquire about the use of laminated ribs, and how they may provide some of the elasticity of "feathering", without so much loss of desirable strength?<br /><br />Thumpe<br /><br />P.S. The 1890's Knabes that I have use laminated ribs that are wide and shallow: seeming to indicate, to me at least, that wide ribs are NOT necessarily an indication of a purely CC board; but rather that this arrangement was chosen to provide a wide glue surface ( perhaps also wise because of the brittleness of hide glue) and make best use of a laminated rib's elasticity, without the undue stiffness that I suspect taller ribs would impart.</div></td></tr></table> <div id="_origMsg_">
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Ron Nossaman <rnossaman@cox.net>; <br>
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<pianotech@ptg.org>; <br>
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Re: [pianotech] GH-1s <br>
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Thu, Dec 20, 2012 5:52:19 PM <br>
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<td valign="top" style="font:inherit;">On 12/20/2012 11:06 AM, David Love wrote:<BR>> How many fixed end formulas are there?<BR><BR>Not many, but I've found I can't assume anything.<BR><BR><BR>> Of course in actual practice<BR><BR>Yes, yes, yes.<BR><BR><BR>> Google it and look<BR>> it up.<BR><BR>I have the formulas, but as I said, I've found I can't assume anything.<BR><BR><BR>> But if we<BR>> use those different formulas and all other parameters remain the same then<BR>> the simple ends beam will be a much sturdier beam than the fixed ends one by<BR>> a factor of 4.<BR><BR>This is where I was going. These calculations are done with full section simple beams. After feathering, a fair bit of strength is given up. I did some calculations and deflection tests years back that indicated around a 16% loss of strength. Calculated with simple ends, this loss is fairly closely cancelled by
gluing the final rib form into the rim, and what small panel compression that exists also compensates. So my conclusion was and is that the simple end full section calculation ends up being pretty close to the reality after it's built. A fixed end calculation showing a beam of some specific dimensions to be four times stiffer (however you care to describe it) under a given load than a simple end formula produces a beam of 1/4 the stiffness of a simple end calculation to produce a given deflection under a given load. That means to me that, since I've verified to my satisfaction the similarity to the real world of the simple end calculations after feathering and assembly, that a fixed end calculation will produce a rib that, after feathering, will be considerably weaker than the calculations indicate. That is, unless there is some surprise secret windage compensation (perhaps a factor of four?) that hasn't been mentioned just yet. Include a low crown and
a 1°+ bearing load on long ribs with no cutoff, and the numbers say it doesn't work and won't support that kind of load at those deflections without being stiffer than is claimed. So I'm wondering how this works.<BR><BR><BR>> BTW re your other post on hybrid RC&S directed at Nick G's post., I took<BR>> that to mean the hybrid versus RC&S positions.<BR><BR>I didn't care to make that assumption, so I asked.<BR><BR>Ron N<BR></td>
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