On Dec 9, 2009, at 11:56 AM, Mccoy, Alan wrote: > Oops. Looks like I’m guilty of not providing a caveat when I sent > you those spreadsheets in that I hadn’t used either of them or dug > into them enough to verify any of the formulas therein. And it looks > like you took some heat for it. Sorry, Fred and others, for adding > to the confusion. Hi Alan, No need to apologize. The spreads you sent were and are perfectly fine and useful, and are based on the information many of us have relied on: the strength tables provided by the wire companies. Those tables show, consistently, a small but steady increase in strength of smaller gauges compared to larger, when that curve is compared to the tension curve. Best I can tell from Ron's posts (weeding out the dripping sarcasm, insults, and other extraneous material, and then trying to decipher his abbreviated statements), people like Sanderson analyzed a larger sampling of the batch tests on which those tables have been based, and found that the increase in strength of smaller gauges is smaller than the more limited sampling had shown. They decided the difference wasn't very significant, so they developed a mathematical model to calculate predicted break point figures. Hence, most scale people these days simply use a mathematical formula, which relates the strength directly to the cross sectional area of the wire. And this formula yields, as would obviously be expected, no difference whatsoever between break% of different gauges for a given pitch and length. This is a practical solution for scaling spreadsheets, as the differences in strength are so small as to be insignificant in making scaling decisions. In fact, the only place break% matters in making a piano scale is at the very top, and in wrapped strings, since the rest is well within safe margins. And beacuse any given batch will vary somewhat from the predicted value, the trend for smaller diameters to be somewhat stronger is not all that useful: the difference in strengths of various batches of 13 wire means that the one you happen to have could be on the weak side of the spectrum, and this outweighs the small advantage it has on average over 14 (and your 14 might be extra strong). The spreads you gave me are not flawed, just based on a different way of predicting reality than the Sanderson or Hays formulae. Neither will predict the reality of music wire behavior with a lot of precision, since wire varies, and since wire usually breaks due to friction or angles or kinks anyway. Using the spread sheets (and their underlying data) to obtain those figures is really about as valid as using the formulae, best I can tell. The best either gives you is an educated guess. Anyhow, any heat I took doesn't matter to me, as long as I ended up with a little broader understanding. I'm not sure the heat was very useful for the list as a whole, though, as probably more smoke than light was generated. Maybe this post clarifies things a little. If not, I'm sure Mr. N will straighten me out, or at least try to <G>. Regards, Fred Sturm University of New Mexico fssturm at unm.edu -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut.php/attachments/20091209/972bad51/attachment.htm>
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