Phil, Ron, and the rest of you - Phil, are you discounting, or unaware of the Wapin system of bridge pinning? I know Ron is aware of it, though, given his reaction to my raising it in the context of a previous thread about downbearing, I got the sense that he was not favorably disposed towards it, reasons unknown. There is some information on their site http://www.wapin.com/science1.htm , though I don't think it's thorough enough to add any insight into understanding exactly what is taking place at the bridge termination. The patents are descriptive,but, as patents, don't provide the information we would want. (http://www.uspto.gov/patft/index.html - Patent #6,100,457). Assuming that there is some merit to the claims made, it is nevertheless frustrating and disappointing that the business model and licensing agreements employed seem to preclude any useful input into a discussion such as this by those who might otherwise have something to offer. As I see it, you need to decide, from the beginning, whether your inquiry is directed towards understanding the mechanical processes at work, or the more practical aspect of building something that will continue to function for a reasonable length of time. For the most part, questions of loosening bridge pins and crushing notches and caps are of the latter direction. That an angled bridge pin might be more prone to causing cap damage than a vertical one is helpful to understanding piano forensics, but it doesn't, by itself, explain the possible differences in acoustic properties of between each. Phil, you said: >If there was no side offset at all and the pin was straight up and down >then it could easily slide as the bridge moved and the downbearing would >be enough to keep it seated on the bridge at all times. Of course, it >wouldn't sound too good. First, to round out the model, let's assume that the notching is exactly bisecting the pin, not forward or behind. AND, let's assume that even with significant (within reason) downbearing, the notch edge does not deform. OK. Why wouldn't it sound good? Actual, "for-real" downbearing would exert force into the bridge surface. (Oh, also forget about the impedance- related issues for now). Imagine a kind of "pre Big-Bang" scenario where the bridge-string segment is on the same plane as the sounding length, just touching the bridge. A significant amount of impact wave (upward displacement) will escape over the bridge and not be reflected. The string will buzz on the bridge. As you increase the bearing angle, you increase the proportion of attack energy that is reflected, reducing the amount that is available to lift the string off the bridge. Eventually you would reach a bearing angle which would reflect virtually all the (vertical) attack energy. Remember, so far, no pin. With extreme magnification, what would we see at this termination? Before the point of "total energy reflection", some of that attack wave would escape over the edge, aided by the wire's own stiffness. If it were possible to weaken the wire at the exact intersection of the bridge edge (like a mechanical pivot), the inharmonicity of the string would be affected (lower), as would the amount of energy reflected (higher), but, assuming that this weakening had no affect on the wire's elasticity, how does this energy transfer to the bridge? Uh oh! We're approaching dangerous waters! Let's not go there yet. Instead of weakening the wire, we create an angle, which effectively stiffens the wire behind the point we wish to flex. Again, looking very close-up, if we were just dealing with a horizontal termination, how would changing the density of that edge affect the wave energy? Some energy is absorbed by the mass of the termination, apart from any resonance or flexing transfer further along the system. With sufficient angle (downbearing), the string would not lift off the bridge, but, depending upon the frictional coefficient between string and bridge surface, there would be some sliding side to side. That whole part of the strings wave form requires a vertical termination. A bridge pin (vertical). How much force is required to prevent wave energy from slipping around terminating pin? How much, if any less than the 8 degrees at the lower end of Ron's tolerance? So, assuming you had adequate down and side bearing, what's changed by slanting the bridge pin? I don't know. If you assume that the "clamping" mechanism spoken of is an actual part of the interaction of the energy wave and the bridge, i.e, that the string "lifts" the bridge, than that slant would seem essential. Or if you thought that, even with positive front bearing, the string would tend to lift off the bridge (slide up the pin), the slant would be critical. If, on the other hand, the behavior at the termination is more pull (pulse) than lift, the slant seems to become less critical than the side bearing, without which some of the energy of the longitudinal (I'm sure I'm misusing this term) wave would escape. If there is any accuracy to the preceding, then the other issues are our attempts to deal with real world imperfection. Is there any difference between a properly terminated string (side and down bearing) and one where the role of down bearing is fulfilled by the clamping of the front pin? I don't know, but it seems like a reasonable question, and one which, with the right equipment, can be measured. As has been previously raised, we use downbearing for two disparate purposes, termination and board loading. Is it possible for the requirements for each to conflict? Now, as to how them waves git into the bridge, and beyond... David Skolnik "Honey? Where's my super [flame] suit? Family's favorite quote (modified) from The Incredibles At 09:51 PM 4/19/2005 -0500, you wrote: >>Thinking some more about bridge notch crushing. Aside from making the >>cap from some impenetrable substance, one way to reduce bearing stress at >>the notch edge would be to reduce resistance to the upward movement of >>the string. This could be done by reducing side bearing angle and bridge >>pin angle. If there was no side offset at all and the pin was straight >>up and down then it could easily slide as the bridge moved and the >>downbearing would be enough to keep it seated on the bridge at all >>times. Of course, it wouldn't sound too good. I wonder what lower >>limits would be? Has anyone experimented with this. I would think that >>establishing minimum sidebearing angle would be something that some piano >>company has worked on. Is anyone aware of any numbers? Bridge pin angle >>is something that seems less obvious as an item of investigation, but >>perhaps work has been done on that too. Anyone know of anything? >>Phil Ford > >Nothing pertaining to published data, but I have (oddly enough) some >thoughts on the matter. As often as I've found zero or negative bearing in >the killer octave through the years, I have little to no remaining faith >in downbearing being a reliable given. If we can't yet easily go to a >vertical bearing offset from available bridge agraffes, we can at least >try to make the existing slanted pin string offset system more reliable. >Along those lines, reducing offset angle and/or pin angle will only reduce >the quality of termination. Personally, I'm not too enthusiastic about >determining the minimal tolerance here, because it would be very likely to >become the standard. I'm a belt and suspenders kind of guy (with thanks to >Justin Wilson for the concept). I want a built in tolerance pad. I'd >rather attack from a different direction than surrender quietly. That >being the case, I prefer 20° pin slant to 15°, and 10° offset to 8°. The >price for better clamping termination from these angles is paid in cap PSI >loading and resultant deterioration. Given the choice of backing off on >the termination quality to accommodate the traditional delicate capping >material, or providing both a robust termination clamp, and a cap that can >take the PSI levels, I'll work toward the latter. There's a lot of >unexplored territory in this direction. > >Ron N >_______________________________________________ >pianotech list info: https://www.moypiano.com/resources/#archives
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