George F Emerson wrote: > One could argue that the fact that this was a new piano is the problem. > The string was not yet seated to the bridge, and once it was, it would > never ride up again on the pin. The problem with this argument is that > I and many others have observed it in many pianos, old and new. For > decades, if not generations, piano tech's have observed this, spoken of > it, taught it, and written about it. Right, "I tapped the string, and it moved down". If it was up the pin, it would also be off the center of the bridge cap. No one has ever claimed to have noticed that. > The only argument that I have seen in opposition to the idea of strings > riding up on the bridge pins is that it defies logic. How can a string > ride up on the pin, if there is positive down bearing, etc.? There are > two problems with this. First, it under estimates the influence of > friction between the string, under 160 lb. of tension, and the pin. > Secondly, it overlooks the fact that side bearing force is many times > greater than down bearing. I know. Phil Ford and I went over this extensively on list some years ago. > Suppose we built a model with a bridge below the zero-bearing line. Do > you suppose that we could force the string up on the bridge pins to > reflect a reasonable front and back bearing, relying on the surface > tension between the string and pin to hold it at that position? I > suspect you could. I suspect so too, if you're careful. Now, what happens when the impulse pulse of the hammer strike hits the termination? I'd bet the string will go back down to a negative bearing position. Now speculate on a model with adequate pin angle and offset, and a half degree of positive bearing. > Again, I suspect so. I confess that I have not built such a > model. Maybe I will, but for now, I have "bigger fish to fry." So has everyone else, and everyone already knows that strings climb up bridge pins, right? So why bother? As to "bigger fish", it seems to me that the millions in time and damage incurred in correcting a problem that isn't present ought to stop. That's going to take some understanding of what's going on, and that's going to take a willingness to entertain notions more rational than strings climbing up bridge pins by some mysterious and universally unnamed process. > So, Ron, I turn the same question around on you. What measurements or > tests have you done, to prove that strings do not ride up on bridge > pins? I know, I know ... you cannot prove a negative. A lot of little things, including pushing down on strings at the center of the bridge to no effect, when then doing the same at the pins, the string moved. If strings climbed up bridge pins, they would be clear of the cap in the middle too. They aren't. Attached is a photo of an unfortunately very dusty bridge with a straightened wire lying in the groove, held down solid at the back edge of the pin hole. Note the angle. Strung and at pitch, The string will almost certainly not be touching the bridge cap at the pin, because that notch edge is below the line the string describes from it's point of support farther in on the bridge cap, and the agraffe. Tap it down, and it will move. It did NOT, climb up the bridge pin to make that possible. The cap edge was crushed down below the string plane by cyclic seasonal movement of the wood, aided by all that side bearing friction you mentioned, and whatever seating was done through the years to insure the strings weren't climbing up the pins. And no, you can't prove a negative - or anything at all to anyone who already knows different. But I try. Ron N -------------- next part -------------- A non-text attachment was scrubbed... Name: Bridge groove angle.jpg Type: image/jpeg Size: 375148 bytes Desc: not available URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100813/ac600e3d/attachment-0001.jpg>
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