How are you calibrating your go-bars? A scale? Calculated beam deflection? Terry Farrell ----- Original Message ----- From: "David Love" <davidlovepianos@earthlink.net> To: "Pianotech" <pianotech@ptg.org> Sent: Thursday, July 24, 2003 3:51 AM Subject: Re: soundboardinstal again > I've always been curious why people use wedges to prestress the board. Why > not use go bars along the bridge line with which you could actually set the > amount of load you were putting on the board--not to mention distribute the > load in a more controlled way. By doing this, you would then be able to > see how the board reacts under 750, 850, or 1000 lbs and set the bearing > based on where you wanted the board to end up. Though the effect of > various loads can, apparently, be precalculated, I would think there would > still be some variability. This would seem to take that variability, or > lingering doubt, out of the equation. It would also seem to be quite > useful on old boards when recapping them. Since older boards vary quite a > bit in terms of stiffness, this would seem to offer a good way of > determining just how much bearing an old board could take without pushing > it too far. Or is this using a cannon to kill a fly. > > 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 11:59:56 AM > > Subject: Re: soundboardinstal again > > > > David Love wrote: > > > 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? > > > > > > > > > I don't think the method of crowning will make a difference here. What > > compression are you talking about? If you are talking about the SB > > picking up moisture, yes that could make it stiffer. But my observations > > are made with the SB at the same moisture content (or very close) so > > there will not be any additional compression (this compression would > > happen with either a rib crowned board or a panel crowned board). I am > > talking about the difference in SB stiffness (resistance to load) > > between dry clamping into the case and gluing it in. I notice an > > increase in stiffness. I interpret this to mean that a soundboard > > receives additional support from being firmly attached to the case. > > Because I use wedges to pre stress the board before setting or > > adjusting bearing I can feel how stiff the board is. I suppose if you > > didn't use the wedges you may not notice this. The soundboard is like a > > stiffening spring, it gets firmer as you press it down. I notice the > > increased stiffness at the bottom of the pre stressing, the slack area > > at the top seems to remain fairly loose. I usually find I need to lift > > the plate up 2mm or more in the middle and bass. The treble remains > > pretty mush the same. This is fairly predictable and Steinway plates are > > easily adjusted (with the plate dowels not the plate bolts) before > > securing the plate down and stringing. > > > > 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] > > > > > > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives
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