This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment Comments below: Terry Farrell =20 ----- Original Message -----=20 From: "Richard Brekne" <Richard.Brekne@grieg.uib.no> To: <pianotech@ptg.org> Sent: Wednesday, July 31, 2002 1:36 PM Subject: Re: CA gluing Grand Pinblocks....My take on it/ Richard Brekne > Farrell wrote: > >=20 > >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. >=20 > Not sure I follow here... why would side pressure on the pin > by the string result in a shear force... ??? Boy, a picture would be worth a thousand words. I am just talking about = a pin in a hole in maple. Push it to one side. You will have tensional = forces between the pin and wood on the side of the pin where the force = was applied. You will have compression forces 180 degrees to the tension = forces. And you will have shear forces between the pin and the wood = along a plane parallel to the pushing force (90 degrees from the = compression and tension forces). > I see the pin > being pushed away from the string in a sideways direction > with the wood of the bridge on the opposite side of the pin > resisting... ie tension force mainly.=20 > Since the string is "bent" over the bridge to begin with I > dont see much upward force on the pin, and unless the string > is moveing perpendicular to the top of the bridge (as in > tuning) I dont see any turning force either. Arent these the > only two shears possible between the two sufaces (pin and > hole) ? >=20 > >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. >=20 > I see this alright... seems like the brother part of any and > all forces being applied here. Perhaps this is a > misconception ?? >=20 > =20 > > 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. > > >=20 > That seems pretty reasonable on the surface of it... tho I > have even run into a fellow who repairs cracked pinblocks > using a combination of CA and CA exciter, and he swears by > this method. He is a fellow who's education and reputation > make it rather difficult to simply dismiss his ideas. >=20 > RicB >=20 ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/80/04/ed/f4/attachment.htm ---------------------- multipart/alternative attachment--
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