Hi ! While using the thin epoxy coating holes method (and new bridge pins) for pins that don't hold quite enough and little cracks on bridges, I am not very sure of the holding in time of this material. Composite material mixing wood and epoxy will not age the same. Epoxy used in gems (agates) to mask little defects (by inclusion under high pressure) are first quality, and they show their presence in time as they decompose. Epoxy as the kind I use is the same as used for marine work for glass fiber work, and don't have much strength by itself. I believe that it will became brittle and probably dusty in awhile, even if the sounding results are evident and the holding very good at first. Beside, the wood aging will probably be slower once coated, Epoxy is certainly used in restoration of old wood for museum pieces, but then they are suppose to stay in a stable H.R. environment (and not submitted to vibration). All plastics decompose with time, not being a chemist, I can't say what is involved in this process, but would like to find information on it. Any links ? Regards. Isaac OLEG > -----Message d'origine----- > De : owner-pianotech@ptg.org > [mailto:owner-pianotech@ptg.org]De la part > de gordon stelter > Envoye : mercredi 31 juillet 2002 15:35 > A : pianotech@ptg.org > Objet : Re: CA gluing Grand Pinblocks....My take on it/ > Richard Brekne > > > 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 > > > > > > > > __________________________________________________ > Do You Yahoo!? > Yahoo! Health - Feel better, live better > http://health.yahoo.com >
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