In the PTJ, March 1967, a reprint of an article by Karl Jung from the March 1964 issue of Euro Piano, can be found, entitled "Experiences With Repairs On Piano Plates" (translated by Jim Engelhardt). In it he writes: 1. BASIC CAUSES OF BROKEN PLATES a) A bar (strut) or a panel (crossband) is designed too thin (or weak) and breaks when the strings are pulled up to pitch (generally before the piano even leaves the factory). b) When casting the plate an air bubble remains in the mold, causing a "flaw" (hollow space) which can weaken a bar which was originally designed thick enough. c) The individual bars and panels are of different thicknesses in relation to each other; after the casting is poured, the thin parts cool down more rapidly than the thick ones; . . . If . . . one of the bars in the middle cools more slowly than the outer edge of the plate, a "stress" in the casting results, since the still plastic, thick bar in the now-solidified plate later contracts up to 1% of its length, which can result in the plate warping. If a warped plate is now pressed flat by forcibly screwing it to the back, this stress in the casting can become so large that the plate breaks. d) A bar which was broken is welded . . . e) In many plates the bars are broken by incorrect installation of the nose bolts . . . f) The string tensions are excessively high; about 154 lbs. (70kg.) for each treble string and 187lbs. (85kg.) for each bass string is considered normal. However, in some instruments individual strings with up to 396lbs. (180kg.) tension on them have been found. As a safety measure, the Carl A. Pfeiffer Company in Stuttgart has all their strung and chipped backs dropped in order to make certain that the plate can withstand such a shock while under stress. 2. DIRECT CAUSES OF BROKEN PLATES a) In some uprights, a portion of the bottom board is omitted in order to increase the area of the plate. The bottom edge of the plate is supposed to be flush with the under surface of the bottom board, but sometimes it protrudes downward and can break if, for example, the instrument is set down roughly on a stairstep. b) Due to string tensions which are too high in relation to its dimensions, the plate is loaded to its breaking point; a sudden drop in temperature (during the night) causes the (thin) strings to contract more rapidly than the (thick) plate, which increases the string tension and can result in the plate breaking. c) Due to shrinkage of the wood (of the back and the liner . . . ), the plate screws have become "loose" i.e. they may be tight in the wood but they are no longer screwed tightly to the plate, so that the back now bears less of the load. . . d) Due to excessive humidity in the air, the soundboard swells and the crown increases, causing a corresponding increase in the downbearing. The pitch of the instrument rises, with the same result as in case (b); in addition, the bars are under a greater buckling stress. e) By increasing the string tension unevenly (e.g., raising the pitch a whole step, at first pulling up only the center section). It is a known fact that it is always better to first raise the pitch only a half step, pulling up all the strings (if possible, each time pulling up all the strings sounding the same note of the scale), and then, after several days, another half step. By means of sensitive measuring instruments it can be seen that the iron in the bars compresses slightly when the strings are pulled up to pitch . . . If the center section is pulled up by itself, only the adjacent bars are shortened and uncontrollable stresses result, particularly in the tuning pin and hitch panels. End of article. As the article states, if the piano was down a full step or so, the whole middle section would have to be raised to pitch before a danger of a broken plate exists, and then most likely in the plate webbing or hitch pin panel, not the struts or cross bars. It is absurd to think that a professional tuner would be at fault in breaking a plate, given the way pianos and their plates are designed. I would like to add that fixing the broken plate may well be a solution which may avoid court. Vince Mrykalo BYU
This PTG archive page provided courtesy of Moy Piano Service, LLC