soundboardinstal again

[Farrell]

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]
> >
> 
> 
> 
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