---------------------- multipart/alternative attachment In a message dated 2/19/2006 4:36:49 P.M. Pacific Standard Time, Erwinspiano writes: Dave Yes pre-loading the board can give a definite idea about string load it will carry. By pre loadingwe can take the slack out. Since the soundboard is a non linear spring it is going to become more resistant as resistance is applied, providing it's built strongly enough within reason. The whole idea of the pre- stressed method of setting bearing is to compress the board in some uniform way before bearing is set & before it is strung. Pre stressing the boar takes place with the plate in place. By placing wedges between the plate struts & the too tall bridge caps. One simply pounds the board down by hitting the bridge top with a fist & at the same time pushing wedges in under the strut. As the board compresses it becomes more resistant to pounding att some point it the resitance feels like your merely pounding on a Gymn floor & the board won't compress further without undue force & This is far enough & usually about a 3mm or so drop in elevation. It is a tactile sense which develops after doing it a few times. After the board at the main strut is wedged down, then the process is repeated on the next treble strut which nets approx. 2mm compression & then the last which nets about 1mm. The last wedge is not forced down as less bearing is needed here a slight bit of down force at the bottom of the tenor bridge is all that's needed. Compressing the board along the long bridge also forces the bass bridge lower as well & if it has a cantalever I set bearing at zero which will net less than a half degree or less & or the rest can be shimmed to whatever you wish. I usually string the entire tenor treble first, raise it to pitch & then calculate bearing on the bass bridge. Then a nickel is placed under each treble aliquot. Draw a bearing string thru the agraffesor capo cut a V notch in the bridge top until the string just touches front of bridge & aliquot at the same time. These V's become the target height of you final bridge height. The bridge needs a bit more rear ward slope cut into it especially the top 2 treble segments but this is the general idea. This method can also be fine tuned using adjustable plate suspension systems allowing the sweet spot to be determined but usually it isn't necessary. Dale Ron: While you have an unstrung board is it possible to put weights on the bridge approximating the downbearing load you expect to have then reexamine the crown and bearing angles? Would this give an elementary idea of the board's ability to sustain that load? dp David M. Porritt dporritt@smu.edu ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/39/66/64/ce/attachment.htm ---------------------- multipart/alternative attachment--
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