Soundboard Clamping for Downbearing

[Erwinspiano@aol.com]

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In a message dated 12/21/2002 4:52:52 AM Pacific Standard Time, 
mfarrel2@tampabay.rr.com writes:

> Subj: Re: Soundboard Clamping for Downbearing 
>  Date: 12/21/2002 4:52:52 AM 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

                 I left out that I also clamp the board at the belly rail, 
spine and am particularly careful to get the upper most treble edge firmly 
down on the rim either with clamps or by using the preexisting screws and 
holes for the maple trimmed edge that is on most pianos. A small error at 
that spot will yield you (0 ) bearing after the boards glued in and you will 
gnash your teeth.. Actually gluing the board in locates it at its  true and 
final elevation and small mistakes on the top treble cap are easy. Ask me how 
I know?
     You didn't ask but you probably will. How do you get the plate reset on 
the acoustic dowels? I thought you'd never ask. This is a Gravagne idea so I 
cannot take the credit, oh well.
  I use half inch cap screws. This is a large machine type screw with an 
allen head opening in the top. The top is to thick dimensionally to imitate 
the thickness of the original heights of some of the very short elevations of 
acoustic dowels. So the tops are machined to about . 050. Stay with me. Now 
when the time comes to find the height of the new dowels that the plate will 
sit on, these are inserted in the bolt holes. I drill down thru the boards 
thickness only, remember up to now no bolt hole is in the new board, with a 
1/2 inch forstner bit (flat bottom bit) Then I take a 7/16 forstner and drill 
down another 1/4 inch. This allows the threads of the cap screw to bite into 
the rim and not the board as the board will split  as the cap screw is turned 
in if just a 7/16ths hole is drilled  thru the board. Get it? Then a cap 
screw is located in each bolt hole location and screwed down to a reasonably 
low level using a large allen wrench.
  Then the plate goes on. The nose bolts, already installed earlier, will now 
be what now locates the plate height you set earlier. Install the nose bolt 
nuts and accessing the top of each allen head through the plate screw it up 
until you sense it touch the plate. Repeat on each one and there you have the 
jigs set up to mark the dowels for there final and correct height.
    Pull the plate and drill the acoustic dowel holes. I drill a 7/16 hole. I 
use the 7/16 inch hard wood dowel from pianotech which is conveniently 
slightly smaller than the hole so that I can insert the dowels mark the 
height, remove them, cut and reinstall. I use a mirror to see at the level of 
the board so I accurately observe when the dowell height matches the top of 
cap screw height. Does all this make sense or did I leave something out?
     There are a many details in belly work that you must learn to juggle  in 
your head at one time so that all the inter related pieces  fit in to the re 
appropriate spot at just the right time. This is just another one of those 
pieces.  
                    Hey When it turn out it's slick!
                               Dale Erwin

> 
> Wonderful, wonderful. Thank you Dale. This sounds like a system that I can 
> work with.
> 
> Terry Farrell
>  
> Dale wrote:
> >      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
> 


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