On Thu, Dec 31, 2009 at 2:12 PM, <paulrevenkojones at aol.com> wrote: > JIm: > > Did you develop any data with this, take any pictures, create documentation > etc. that would be helpful, write-able up? Please? > Paul, This is a response to your request for further info regarding my rc&s belly load experiment. I've written 3 attempted responses but chucked them...let me try this one. If this response seems coy or obfuscatory, please accept my apologies in advance. I have sincerely put time in to this response, and am trying to be helpful to those like me who are seriously trying to wrap their minds around belly issues. The purpose of my experiment was help me to form a clear visual image of what is happening to a loaded board from a purely structural perspective. No publication was envisaged, as the test process which was already quite time intensive, would have had to take 10 times as long to be reasonably publishable as reliable data. Further, any data published would still have been only "basic research" type data, meaning it would not be appropriate to use this data to formulate concrete belly design protocols, or worse to confuse others by suggesting that it could be directly applied to a belly. So I think I'll give the publishing angle a miss. However, the following are the broad outlines of what i learned which you can take to your own experiments and validate or discard for yourself. The 1/3 scale rig consisted of a rib/bridge system whose rib scale and load values were scaled from a failed rc&s belly I had constructed. The first step of my plan was to construct the scaled test and run it in several permutations, and compare it to my spreadsheet predictions of deflection. The second step was to take the real failed belly, and by reducing the load from 700lb-250lb in measured steps, come up with deflection #s for the real belly, again comparing them to spreadsheet predictions. Third was to compare the behavior of the test to the behavior of the real belly. (side note: comparison of the failed belly to the scaled belly was an essential part of the test.) Since knowing what loads to assign to each rib is a key part of an rc&s design, I wanted to understand how to think about "where the string loads actually go". The design of the experiment seemed a good way to apply actual loads in real time and see what happened. My initial hypothesis was that the calculated loads for each rib should be calculated at the physical places they contacted he bridge. I expected I would be able to nail down specific load distribution numbers. My hypothesis was incorrect; ie, the system is too complex. But I did get a way to think about loads that was more generally supported by the experimental results. I'll share just the broad outlines of this, as these experiments already involve many many unpaid hours or messing about trying to find ways of understanding belly structure and were structured to make sense to particular way my brain likes to process information. Many of you bellymen are way beyond these observations; they are presented here for those like me who are trying to make sense of this system. All of the points have been discussed on this list before I think. They point towards a way of approaching the problem intellectually. They are not presented as a recipe. Please remember that the following refers to an *rc&s board only.* 1- deflection of an individual stand alone rib unattached to any bridge structure is quite linear and conforms to the deflection formulae. 2- the addition of the bridge adds significant stiffness to the structure. This was not intuitive for me. The bridge not only evens (bridges) the loads, but it actually adds stiffness to the rib assembly. 3- the addition of the board and glue down to the rim adds stiffness to the system 4-There are stiffness losses (though not from compression set as in compression boards) related to beam relaxation and initial beam springback(after ribs are removed from the laminating caul) 5-***a biggy*** the deflection of the entire system, ribs/bridge/board/rim, still behaves in a relatively linear fashion (remembering that my experiment refers only to an rc&s board, not a compression board). Which by the way explains why rc&s structures are not as picky about downbearing as compression boards 6- ***the punch line*** the load that each rib is expected to carry can be mathematically be described as a coordinate point in a trend. If that sounds like greek to you, open up an excel file, enter 2 columns worth of x and y coordinates, click on the graph wizard, and graph those points as an x.y scatterpoint plot. Then add a "trendline" to the plot (this is all accessible through excel wizards). There are a bunch of trendline choices, play with the polynomial trends and see what they do to your plot points. The big thing I learned from these experiments was that anything we see happening structurally or tonally will be observed as a trend; ie, a tendency for things to go a certain way under a certain set of circumstances. and to progress in an "even" or rather "trended" fashion. Look for a "tendency" as opposed to a recipe. When I ran the tests, the "data" I collected was not only deflection #s. Equally, or more importantly, with my own eyes, I watched as I saw my predictions confirmed or negated right on the bench. Since I have a visual intelligence the combination of all the numerical and visual "data" etched itself in my brain. Together with the visual nature of the excel graph/trends, the visual observation and deflection# constructed a way for my brain to conceptualize the belly's behavior. So the bottom line, which has also been stated numerous times by seasoned belly experts on this list, is, the only way to get a handle on the #'s is to construct a way for your own brain to embrace the complexities involved. Forget about hard #'s and become comfortable with the concept of mathematical trends. Excel is accessible. Mess around with it. Any time you get stuck the internet has the excel experts answering questions quite effectively. Ask the list "how to do" specific formulae when you get stuck. Mess around with excel and mess around some more...its really quite entertaining. I hope that doesn't sound coy. Its just the way it is, just like there are no hard #s for the most beautiful tuning or voicing. ps. I can post pics of the first test rig(I went through 2 versions of the test rig) when I get home, if you would like...away visiting right now. Your fellow traveler, Jim I grandpanosolutions.com(almost launched, if IE-7 would stop blowing up) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100103/060ae7c6/attachment-0001.htm>
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