Farrell 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. Not sure I follow here... why would side pressure on the pin by the string result in a shear force... ??? 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. 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) ? >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 see this alright... seems like the brother part of any and all forces being applied here. Perhaps this is a misconception ?? > 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. > 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. RicB
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