This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment Dale, Carl, et al, As I understand it, the vertical hitchpin arrangement was developed as a = manufacturing expediency. It enables the manufacture of the bridge = assembly-including drilling, notching and pinning-prior to anything = being fitted to the piano. The finished bridge is simply glued to the = soundboard and the whole assembly is then glued into the piano. The = plate elevation is set to the bridge using the threaded bolt system = concurrently developed with the hitchpin system. String bearing, i.e., = soundboard loading, is then established by the vertical alignment of the = strings on the vertical hitch. The vertical hitchpin system by itself = has nothing to do how much string bearing, or soundboard loading, is = required or is present. It simply provides a method of adjusting that = load after the piano is strung.=20 The purpose of string "downbearing" is to place load on the crowned = soundboard assembly and deflect it from its as-installed condition. = Considering the soundboard assembly as a large, irregularly shaped disc = spring, this load provides the piano builder with a means of increasing = its stiffness without increasing its mass. How much string bearing, = i.e., string downforce against the bridge, any individual soundboard = assembly must have for best performance is a function of the soundboard = design and, to some extent, such factors as the design and shape of the = rim, the relative tensions of the string scale, the length of the string = backscale, etc.=20 Mostly, how much loading any specific soundboard must have is a function = of how massive and how stiff the soundboard assembly is. This is not a = universal constant. Dale's string deflection numbers would not work all = for one of our boards. As to whether they would work for one of = Baldwin's current boards-I can't say. With the Accu-Just system Baldwin = has used a fairly light crown radius-72' (about 22 m) if I recall = correctly-machined into the ribs. I believe the rib-to-soundboard press = cauls are crowned the same. I don't recall the MC of the board at the = time of ribbing, but I don't recall it being overly dry. Excessive = loading-and it doesn't take much to be excessive-on one of these boards = will overload it, hence the relatively shallow string deflection angles = and the traditionally percussive, short sustain, sound. (And I think = that's 0.5%, 1.0% and 1.5% downforce as a funciton of string tension as = indicated by 1, 2 or 3 lines of gradation each indicating 17 minutes of = arc on the Baldwin bubble gage, not 0.5=B0, 1.0=B0 and 1.5=B0 of string = deflection). Personally, I would load them just a bit more than the = Baldwin specification calls for always being aware of the relatively = shallow initial crown specification.=20 If you're replacing a soundboard in a Baldwin-or if you have converted = some other piano to the vertical hitch pin system-and you're using your = own standard soundboard design-I would recommend that you use the string = deflection angles you're already accustomed to. As Ron has indicated, = you want to end up with the string about 4 to 5 mm off the plate = surface. You have a bit more leeway with this on a Baldwin plate = designed to accomodate the vertical hitch; the hitchpin panel has been = made some thicker to accommodate the additional torsional stress of the = string riding higher on the pin. Be very careful with other pianos and = other plates. Of course, string bearing can be measured and altered after it has been = set. That is one of the inherent advantages of the system. Why that = statement would appear in the Baldwin instruction sheet baffles me. What = you will find, though, is that once you have established some amount of = string deflection-how much varies with the soundboard design and string = backscale length-tapping the strings down further won't give you much = more measurable string deflection. Except at the extreme end of the = tenor bridge and, sometimes, at the low end of the bass bridge, the = soundboard will just continue to deflect as you tap the strings down. = Yes, I know, there should be some noticeable change in the string = deflection angle, but there won't be. At least none that will be readily = measurable. Try it and see.=20 Perhaps Baldwin took that approach to keep technicians from continuing = to tap strings down until they had achieved a condition of permanent = reverse crown. If so, it didn't work since that is an all-to-common = problem with the system. I've fielded questions from technicians who = considered it a matter of poor workmanship to have the strings riding up = on the hitch and tapped them fully down against the plate surface. = Ruining the soundboard and any semblance of tone quality in the process, = of course, but at least the strings were now 'properly' seated. This is an excellent string termination system, the benefits of which = extend well beyond manufacturing expediency. I have an idea if it was = understood some better it would also be used more frequently. Del Delwin D Fandrich Piano Designer & Builder Hoquiam, Washington USA E.mail: pianobuilders@olynet.com Web Site: www.pianobuilders.com ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/c7/68/0d/f5/attachment.htm ---------------------- multipart/alternative attachment--
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