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

[gordon stelter]

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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