soundboardinstal again

[David Love]

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]
>