John: I don't know if you are rib crowning or compression crowning, but might that difference be explained by changes that occur due to compression after the board is installed? David Love davidlovepianos@earthlink.net > [Original Message] [link redacted at request of site owner - Jul 25, 2015] > To: <davidlovepianos@earthlink.net>; Pianotech <pianotech@ptg.org> > Date: 7/22/2003 5:18:04 AM > Subject: Re: soundboardinstal again > > David Love wrote: > > A point made earlier in this discussion about the tightness of fit around > > the perimeter brings up a question. I know that some soundboard installers > > prefer to do the bridgework with the board out of the piano, i.e. notching > > and pinning. So, they lay in the board, and put the plate in on top, clamp > > in a few key places, wedge the board down under the struts and set the > > bearing, take everything out and notch and pin the bridge. With a certain > > amount of gap around the perimeter of the board, you would think that the > > board would move outward slightly in the wedging process such that setting > > the bearing would give a different result than when the board was actually > > glued in. Any comments on this method and whether it presents a problem? > > > David, > > I set DB with the bridge glued on and the SB dry fit in the case. The > plate is clamped in with wood spacers between the plate bosses and the > SB. Wedges are used to pre stress the board so that DB can be set with > the SB at its point of equilibrium. Later after all the bridge work is > done and the SB is glued in DB is checked before the bolts and screws > are installed. I am not sure about the sliding problem you mentioned (I > can't see this happening) but I always find that the plate needs to be a > little higher. It seems that the SB is a little stiffer (about 20% ?) > when it is glued in. I can tell this when I install the wedges. This > would indicate that the rim does contribute in some way to the stiffness > of the SB. Weather it does this by preventing the ribs from sliding or > by preventing them from rotating I am not sure. I do not have the > information in front of me but as I recall that a beam that is clamped > at its ends is stiffer than one that is not. I am now building and > installing my 200th Soundboard (A guess based on dwindling shop supplies > and fatigue) and have found this increase in stiffness to be predictable. > > John Hartman RPT > > John Hartman Pianos [link redacted at request of site owner - Jul 25, 2015] > Rebuilding Steinway and Mason & Hamlin > Grand Pianos Since 1979 > > Piano Technicians Journal > Journal Illustrator/Contributing Editor [link redacted at request of site owner - Jul 25, 2015] >
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