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

[gordon stelter]

Yes. I'd use the West system too, and waft over it
gently with a heat gun to thin the stuff and really
get it to penetrate the wood! I read an article once
that said the author believed such impregnation 
helped vibrations travel, and I must concur! Epoxy is
denser than wood, and therefore transmits vibrations 
better. On uprights I have no problem coating the
entire bridge with it for this very reason, and may do
it on a grand someday although it does make the bridge
encapsulated in shinyness- not everyone's esthetic cup
of tea! Still, a superior sound-producing and totally
-moisture-impervious bridge is more important than
minor cosmetic concerns, in my book!  Scrape the
coated bearing surfaces flat with a razorblade, and
you will then have an excellent surface for simple
pencil graphite to stick to. Easy and very effective!
--- Farrell <mfarrel2@tampabay.rr.com> wrote:
> 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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