Soundboard Installation & MC

[Delwin D Fandrich]

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Dale,

You are referring to an effect you notice at the point of initially =
gluing the soundboard assembly to the rim. Certainly the soundboard =
assembly is stiffening up. You are changing it from a free-floating =
panel to a clamped-edge panel. Apples and pomegranates in the context of =
this discussion.=20

I (and, presumably, M&H) am referring to an effect expected to last =
through the ages. I would respectfully suggest that you read up on the =
phenomena of wood creep. Look specifically at wood deformation under =
load over extended periods of time.

Del
  ----- Original Message -----=20
  From: Erwinspiano@AOL.COM=20
  To: pianotech@ptg.org=20
  Sent: April 23, 2002 5:54 PM
  Subject: Re: Soundboard Installation & MC


  In a message dated 4/23/2002 9:08:29 AM Pacific Standard Time, =
pianobuilders@olynet.com writes:



    Subj:Re: Soundboard Installation & MC=20
    Date:4/23/2002 9:08:29 AM Pacific Standard Time
    From:pianobuilders@olynet.com
    Reply-to:pianotech@ptg.org
    To:pianotech@ptg.org
    Sent from the Internet=20




    ----- Original Message -----
    From: "Farrell" <mfarrel2@tampabay.rr.com>
    To: <pianotech@ptg.org>
    Sent: April 23, 2002 4:12 AM
    Subject: Re: Soundboard Installation & M=20

                    Del, Ron,Terry
     =20
                    I Read each of your post and I think I have a =
diiferent or additional  point of view  about the comments about the rim =
having  having no effect on holding crown. The rim in my view at least =
is a supporting agent to crown.
      Let me explain. Although from what my colleagues  Ron /Del have =
stated about emc at the time of ribbing and to the precrowning of ribs =
and such I can say our methods are similar except for the redesign =
factor.
        This to say were all building a pretty stiff soundboard system. =
When I'm setting my bridge height for bearing I do this as a dry fit =
with clamps and screws and such. With the plate installed over the board =
and screwed and fastened down I then prestress the board with wedges =
before cutting down the tops of the bridge to the height I want. Thus =
setting my bearing.
       Once I,m happy with that I remove every thing and finish the =
bridge, glue it on the board and glue it in the piano somewhere between =
6 to 7% emc or so.
    In spite of the board being very stiff I find that it is much more =
easly forced down during my bearing pre-stressing procedure and it =
demonstrates much more flacidity( is that a word?) than after it is =
glued to the rim.
       With the rib ends  and board perimeter at last are glued to the =
rim the board takes on an dramatic increased dimension of stiffness.=20


     So I will humbly disagree that the rim is not a supporting agent of =
the crown for without it the strings would squash more of the crown out =
as the rib ends and board edge are moving outward and lifting. Without =
the Rim  the rib ends and board edge  would still woggle around and lift =
when depressed in the middle.
    The other isuue is that although the bearing is essentially a =
downward force it does push out wards and into the rim at least a bit =
once the board IS glued in. Since we have an arched system, vaguely =
similarto the concept of a flying buttress used in cathedral =
construction,it is a resistive element.
  How much is I think part of the debate here.=20
      I'm not saying the rim does alot to hold a crown from diminishing  =
I'm just saying it's a supporting agent which aids the boards stiffness.
  >>>>>...Just my two cents worth--------Dale Erwin>>>>>>>>>>
      =20



    Tery wrote
    > What argument would there be for drying prior to installation?
    Del wrote
    With a compression-crowned board? It is easier to work with and glue =
into
    the rim if it is dry, having little crown.

    With a rib-crowned board there is just the matter of consistency. =
You don't
    want the board too dry or too wet--both have a negative affect on =
the glue
    bonding strength. We rib our boards at 6.5% and glue them in at 6.5% =
to
    7.5%.


    >Terry
    > Has this become the "standard" because the "masters" did it that =
way back
    when it was a fact that the rim supported the crown?
    Del
    It has never been a 'fact' that the piano rim supports the crown =
though many
    have believed this over the years. Some argument can be made that =
beveling
    the rim--as is the practice of some--does have some nominal effect =
on
    soundboard crown, but it is very short-lived. Consider that this =
effect is
    greatest in the treble region of the soundboard panel and yet this =
is the
    region that typically looses its crown--certainly the stiffness =
related to
    crown--the earliest in a compression-crowned soundboard system. =
Obviously,
    the effect is minimal.


    >Terry
    > I suppose if you flat ribbed it and dried the bajeezers out of it, =
the rim
    just might help to hold a bit of crown - at least until it got off =
the
    showroom floor!

    If the rim actually did support crown you'd never see a M&H with a =
flat
    board!

    Wood--primarily the spruce used in the soundboard system--simply has =
too
    much compliance and is to susceptible to long-term creep for the rim =
to have
    any real function in sustaining crown.

    Del






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