> Mason & Hamlin said that one purpose of the bushings was to center the > drill bit in the plate's hole, so that would be one downside. > > --Cy-- Other piano manufacturers besides M & H will tell you that the primary, if not the sole, purpose of tuning pin bushings is to center the drill in the hole. But, is that really optimal? If not, is that really a "downside?" Given the angle of the drill (approx. 7 degrees) if the drill is centered at the top of the bushing, it is considerably off-center at the bottom of the bushing. I would argue that it would be preferable to maximize the bushing material on the side that will be compressed by the string tension, which means that the drilling through the bushing needs to be deliberately off center, opposing the pull of the string tension. Look at any piano with bushings, and you will likely see a gap between the tuning pin and its bushing on the side opposite the string tension, and the bushing compressed on the opposite side. I cannot speak for Yamaha, but I suspect that this is, at least in part, their reason for not driling a center hole, so a center-punch can be used to mark the center for drilling, off-center, opposing the pull of the string. Using the bushings to center the drill may be "good enough" to prevent direct contact between the tuning pin and the plate, but deliberately off center towards the "top" of the hole would be even better, IMO. Years ago, I restrung an S&S grand (with no bushings). Servicing it regularly in a university environment, I had been irritated by several pins "ticking" when I tuned it. Every movement of the tuning pin, in either direction, was accompanied by an audible "tick." I marked the offending pins before removing the strings and tuning pins. After the pins were out, I observed a visible impression of the tuning pin threads, on the inside of the plate holes, in every tuning pin hole that had been marked as a "ticker." The thread-marks were always, and only, on the side of the hole toward which the pin would be pulled by the string tension. I took this as clear evidence of direct, metal-to-metal, contact between the tuning pin and the plate webbing. I reamed out the tuning pin holes, to enlarge them enough to add bushings. This proved to me that tuning pin bushings serve at least one purpose, to prevent direct metal-to-metal contact between the tuning pin and the plate. I have no experience with open-face pinblocks in a production piano, but I suspect that there is a measureable gap between the tuning pin and its hole in the pinblock on the side opposite the pull of its string tension. While it is clear that an open-face pinblock provides optimal support to the pin higher on the pin, a tuning pin bushing provides similar support, when the drilling optimizes the bushing material on the effective side of the hole. So, what is the purpose of the tuning pin bush? I would say: 1. To prevent direct metal-to-metal contact between the tuning pin and plate. 2. To center the pinblock drilling in production, or in some cases, to deliberately off-center drilling, on the side opposite the pull of the string. 3. To provide support to the tuning pin as high as possible, if not as well as with an open-face pinblock, the next-best thing to it, Frank Emers
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