CA gluing Grand Pinblocks....My take on it/ Richard Brekne

[Joe And Penny Goss]

Hi Gordon,
We may be looking at two different situations.
The repair of a bridge that has cracked so badly that the pins have shifted,
is imho not a place where CA can or should be used,
I am thinking more along the lines of where there are small cracks eminating
from the pin or where the wood has been crushed by the swings in humidity
and the pin is now loose in the hole. I do not consider CA for a delaminated
bridge or pin block a repair but a bandaid and not worth the effort.
As to gluing the string the string to the bridge, it does not bother me to
have that.
What would cause me concern would be to have the piano below pitch, treat
the pins, then tune. In this process the posibility of a string rendering a
week later and the unison being wildly out of tune would not be to my
liking. But up to pitch , where is it going to go?<G>
Joe Goss
imatunr@srvinet.com
www.mothergoosetools.com
----- Original Message -----
From: "gordon stelter" <lclgcnp@yahoo.com>
To: <pianotech@ptg.org>
Sent: Wednesday, July 31, 2002 7:51 AM
Subject: Re: CA gluing Grand Pinblocks....My take on it/ Richard Brekne


> Treat them at tension and you will be gluing them into
> the wrong place, or gluing the bridge to the string.
> --- Joe And Penny Goss <imatunr@srvinet.com> wrote:
> > Hi Terry,
> > Would not most of the shear factor be removed by
> > treating the bridge pins at
> > tension?
> >
> > Joe Goss
> > imatunr@srvinet.com
> > www.mothergoosetools.com
> > ----- Original Message -----
> > From: "Farrell" <mfarrel2@tampabay.rr.com>
> > To: <pianotech@ptg.org>
> > Sent: Wednesday, July 31, 2002 6:59 AM
> > Subject: Re: CA gluing Grand Pinblocks....My take on
> > it/ Richard Brekne
> >
> >
> > > I should think that a cracked bridge pin hole
> > repaired with CA (or any
> > other adhesive) would be subject to shear,
> > compressive and tensional forces.
> > When the piano is strung and the side pressure is
> > applied to the pin by the
> > string, you will have a shear force between the pin
> > and the maple on the
> > inside of the bridge pin hole. You will also have
> > compressive forces applied
> > to the CA that is filling the crack on the side of
> > the bridge pin opposite
> > the string. As the bridge pin tries to move away
> > from the string, it will
> > apply outward forces (tension force) to the CA layer
> > and/or maple on the
> > inside of the crack (at the edge of the bridge pin
> > hole) - trying to once
> > again split the bridge cap open.
> > >
> > > I would think that a CA repair on a bridge with
> > loose pins would likely be
> > a reasonable approach (mostly just compression
> > forces), but I don't think I
> > would be comfortable repairing a cracked bridge with
> > CA. I'd break out the
> > West System epoxy.
> > >
> > > Terry Farrell
> > >
> > > ----- Original Message -----
> > > From: "Richard Brekne"
> > <Richard.Brekne@grieg.uib.no>
> > > To: <pianotech@ptg.org>
> > > Sent: Wednesday, July 31, 2002 7:26 AM
> > > Subject: Re: CA gluing Grand Pinblocks....My take
> > on it/ Richard Brekne
> > >
> > >
> > > > Joseph Garrett wrote:
> > > > >
> > > > > Richard,
> > > > > Your statement: "And in the case of the bridge
> > pin there is nothing to
> > exert
> > > > > any shear force on the CA itself so it should
> > just......."
> > > > > NOT! How, prey tell, did the bridge become
> > cracked, in the first
> > place?
> > > > > answer: by the force of the piano wire trying
> > to straighten out at the
> > > > > bridge pins/bridge! If that ain't shear stress
> > than I don't know what
> > is!
> > > >
> > > > I understood shear stress to be stress applied
> > parallel to
> > > > the sufaces involved. In the case of bridge pins
> > that would
> > > > require either a force applied to twist the pins
> > (as a
> > > > tuning pin turns in the pin block) or a force
> > pulling or
> > > > pushing the pin up or down the length of the
> > bridge pin
> > > > hole. The force you refer too I understood to be
> > more a side
> > > > ways presure exerted from the string.... which
> > would be more
> > > > perpendicular to the hole eh ?? Perhaps some
> > amount of shear
> > > > stress might be applied from the strings pulling
> > on the pins
> > > > as the string moves under tension
> > adjustments....but....
> > > >
> > > > I thought bridge cracking was a caused mainly by
> > a
> > > > combination of climatic problems and side ways
> > pressure on
> > > > the side of the bridge pin hole opposite the
> > strings ??
> > > >
> > > > Please correct / expand if this is in error :)
> > > >
> > > > > I just made a bridge for a tech, who used CA
> > to "fix the cracked
> > bridge". He
> > > > > didn't like the look of it and sure as hell
> > didn't like the
> > sound.....So,
> > > > > New Duplicate Bridge. I won't tell you what it
> > cost, but I ain't a
> > cheap
> > > > > date.<G> Actually, the duplicated bridge was
> > better than what you
> > would see
> > > > > in a top notch grand and this was for a
> > Chickering Upright. I know
> > from long
> > > > > experience, that that bridge will meet/exceed
> > the sound quality of the
> > piano
> > > > > when it was new. Not braggin', just have found
> > this to be the case.
> > > >
> > > > Braggin is cool.... grin at least the way you do
> > it  ! In
> > > > any case I believe you. Next time I am over
> > there you can
> > > > show me your stuff eh ?? My Dad lives in Salem.
> > > >
> > > > > Best Regards,
> > > > > Joe Garrett, RPT, (Oregon)
> > > > >
> > > > > I'm never lost, because everyone is telling me
> > where to go. <G>
> > > >
> > > > Cheers !
> > > >
> > > > RicB
> > > >
> > >
> >
>
>
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