<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <META content="MSHTML 6.00.2600.0" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY> <DIV><FONT color=#ff0000>Comments below:</FONT></DIV> <DIV><FONT color=#ff0000></FONT> </DIV> <DIV><FONT color=#ff0000>Terry Farrell</FONT></DIV> <DIV> <SPAN id=__#Ath#SignaturePos__></SPAN> </DIV> <DIV>----- Original Message ----- <DIV>From: "Richard Brekne" <<A href="mailto:Richard.Brekne@grieg.uib.no">Richard.Brekne@grieg.uib.no</= A>></DIV> <DIV>To: <<A = href="mailto:pianotech@ptg.org">pianotech@ptg.org</A>></DIV> <DIV>Sent: Wednesday, July 31, 2002 1:36 PM</DIV> <DIV>Subject: Re: CA gluing Grand Pinblocks....My take on it/ Richard Brekne</DIV></DIV> <DIV><BR></DIV> <DIV>> Farrell wrote:<BR>> > <BR>> >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.<BR>> <BR>> Not sure I follow here... why would side pressure on the = pin<BR>> by the string result in a shear force... ???</DIV> <DIV> </DIV> <DIV><FONT color=#ff0000>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).</FONT></DIV> <DIV> </DIV> <DIV>> I see the pin<BR>> being pushed away from the string = in a sideways direction<BR>> with the wood of the bridge on the opposite = side of the pin<BR>> resisting... ie tension force mainly. <BR>> Since the = string is "bent" over the bridge to begin with I<BR>> dont see much upward = force on the pin, and unless the string<BR>> is moveing perpendicular to the = top of the bridge (as in<BR>> tuning) I dont see any turning force either. = Arent these the<BR>> only two shears possible between the two sufaces (pin and<BR>> hole) ?<BR>> <BR>> >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.<BR>> <BR>> I see = this alright... seems like the brother part of any and<BR>> all forces = being applied here. Perhaps this is a<BR>> misconception ??<BR>> = <BR>>  <BR>> > 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.<BR>> ><BR>> <BR>> That = seems pretty reasonable on the surface of it... tho I<BR>> have even run into a = fellow who repairs cracked pinblocks<BR>> using a combination of CA and CA = exciter, and he swears by<BR>> this method. He is a fellow who's education and reputation<BR>> make it rather difficult to simply dismiss his = ideas.<BR>> <BR>> RicB<BR>> </DIV></BODY></HTML>