Soundboardcrownpress

[gordon stelter]

Has anyone built a soundboard press/rib cutting system
which insures that the apogee of the board's crown is
right under the bridge, where it seems, for
durability, stability and tone, that it ought to be?
Due to the shape of pianos, ribs cut at a constant 
radius and glued to the board in a constant radius
press will place the apogee alongside the bridge, in
many areas.
     Is the correction of this what Chris Robinson
refers to as the "catenary arc"?
     When I was "laid-up" a few years ago I spent
considerable time designing a press for this, but
never built it. It depended upon screwing/clamping the
bridge core to a series of "ribs" ( actually slats in
the place of the ribs, perhaps of carbon fiber or some
other uniform, flexible material )  then pressing upon
the bridge core with a reverse pressure reflective of
down bearing, so that these slats assumed a natural
curve with the apogee at the bridge line.
    Their ends protruded beyond a mock-up rim, and
slid over it. Then, bolts underneath held them in
place, or cauls could be cut to this shape. This, then
formed the "dishing" table.
     $10 to the first who builds this, or an
improvement thereof.
     Thump

--- Ron Nossaman <RNossaman@cox.net> wrote:
> 
> >Environment humidity was about 60%, that's normal
> in Belgium (but after
> >reading other mails, I think to high for gluing
> ribs)  Concerning the
> >humidity of the wood it self, I can't tell you.
> >
> >I made the board and placed it upside down (has to,
> otherwise you will
> >get reversed crown)  in the press for gluing on the
> ribs. The wood of
> >the press bends just enough when you blow the hoses
> for receiving about
> >1 cm of crown
> >The strange thing is when I eye-checked it,  the
> crown seems to have
> >disappeared (ie, when the board came out of the
> press, one really saw
> >the crown) .  But now, when I'm heating it to dry
> before gluing it in
> >the piano, and checked it with a straight piece of
> lumber I have crown
> >(about 12, 13 mm) across the ribs, the highest
> point of the board is
> >where it has to be, and I see  a little bit of
> negative crown along the
> >ribs (although this could be caused from heating
> the board, so it'll be
> >warmer in the center as on the ends)
> 
> Peter,
>  From your description, I wouldn't expect your board
> to have done anything 
> else but go flat when you dried it. Why would you
> dry it to glue it in the 
> piano when you apparently didn't to glue on the
> ribs? I don't understand. 
> As Del said, I hope you can get the ribs off without
> destroying the panel 
> so you can start over again. In the four years or so
> that you've posted to 
> the list, at least a month's worth of reading has
> been posted on soundboard 
> crowning methods and expected results. Please go
> back and read some of this 
> stuff, particularly the differences between rib
> crowning and panel 
> (compression) crowning.
> 
> Ron N
> 
> _______________________________________________
> pianotech list info:
https://www.moypiano.com/resources/#archives


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