Hi Isaac, Valid points Go to Google.com and search plastics decompose. Plenty to look at there and ponder. Joe Goss imatunr@srvinet.com www.mothergoosetools.com ----- Original Message ----- From: "Isaac OLEG" <oleg-i@wanadoo.fr> To: <pianotech@ptg.org> Sent: Wednesday, July 31, 2002 8:35 AM Subject: RE: CA gluing Grand Pin blocks....My take on it/ Richard Brekne > 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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