I guess it would lessen it. But wouldn't you want the pins in their original position? That is why I differentiated between a bridge with cracks and a bridge with loose pins. I suspect overcoming cracks effectively and long term, is just too much to expect of CA. Terry Farrell ----- Original Message ----- From: "Joe And Penny Goss" <imatunr@srvinet.com> To: <pianotech@ptg.org> Sent: Wednesday, July 31, 2002 9:32 AM Subject: Re: CA gluing Grand Pinblocks....My take on it/ Richard Brekne > 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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