Soundboard Clamping for Downbearing

[Erwinspiano@aol.com]

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In a message dated 12/19/2002 4:42:57 PM Pacific Standard Time, 
mfarrel2@tampabay.rr.com writes:

> Subj: Soundboard Clamping for Downbearing 
>  Date: 12/19/2002 4:42:57 PM Pacific Standard Time
>  From: <A HREF="mailto:mfarrel2@tampabay.rr.com">mfarrel2@tampabay.rr.com</A>
>  Reply-to: <A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
>  To: <A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
>  Sent from the Internet 
> 
>        Terry


           Well, it certainly is way easier to do the bridge notching / 
pinning, etc., out of the piano. 
  So I do the dry fit set up this way. In my climate I like the board to have 
taken up some moisture but something like it would experience with the R. H.  
about 40% or EMC about as you said 9% or so. I locate and temporarily install 
my bridge to the board with soundboard buttons and screws, one between each 
rib and one through only the ribs in the low tenor that have the feet thing 
and cutout between them. Usually that's only 2 or three. I Install the board 
dry by drilling holes for dry wall screws thru the board and into the rim 
where the acoustic dowels were located. No magic here. These holes will 
eventually disappear when the holes for acoustic dowels are drilled or fill 
them with hammer shank if a different support system is used.
  Next install your plate with the nose bolts for support. Install about 8 or 
10 screws in the pinblock, usually next to each strut. I set the plate so its 
elevation at the last bass end bolt hole is where it was originally which 
means the plate boss is fairly close to the board. I have a shim between the 
boss and the board. I put a clamp and block holding down the plate to prevent 
it from coming up in the bearing procedure.
    I then turn up my nosebolts which were installed low. This includes the 
bass strut nose bolt and cap nut too. I pre-stress the board with a shim at 
each plate strut to simulate some string load as I've described before. I Cut 
my bearing notches to determine where the bridge height will be. Pull the 
plate & board plane the top of the bridge reinstall check and make final 
corrections to height and bridge slope. Pull it out remove the bridge, drill, 
notch & pin and the other details.
    After the board is glued in I always recheck my bearing and adjust my 
plate a bit if needed. This is a great method but you'll find your board ever 
much stiffer when you go thru the pre-stress bearing check at this point 
because the bridge and board have been glued on and everything has gotten 
stiffer. Which means your bearing may be more than you bargain for. With this 
method I've learned to set the distance bearing on the stingy side especially 
from about note 60 ish on down. With Steinways it's possible to shim aliquots 
up if too much bearing is attained. Flexing the plate up with the nosebolts 
is good for about 1/4 turn max. in my book with Steinways and none in Masons 
as the plates are too stiff to flex.
       Hope that helps
        Dale Erwin
    

> 
> One thing I have never been able to clearly picture in my head (or rather, 
> one of many). If I wish to notch the bridge outside the piano, I need to 
> temporarily mount bridge to board, set board into case and set plate at 
> final resting height (on dowels or adjustable bolts, etc.). When I have the 
> plate in, how do I clamp the board down to the rim securely for determining 
> final bridge height? At what MC do I have the board for this procedure (I 
> would assume equilibrated with room RH - maybe 9%)? Looking a step further, 
> if I then dry the board down prior to installation and then glue the board 
> to the rim, can I be pretty sure the board will crown right back to the 
> test height when I measured for bridge height? Just can't get this process 
> straight in my head where I can see that all will work out.
> 
> Thanks for any thoughts.
> 
> Terry Farrell
>  


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