<!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 5.50.4134.600" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B> <A title=davidlovepianos@earthlink.net href="mailto:davidlovepianos@earthlink.net">David Love</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">pianotech@ptg.org</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> August 31, 2001 7:51 = PM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: split bridge</DIV> <DIV><BR></DIV> <DIV><FONT size=2>Joe:</FONT></DIV> <DIV><FONT size=2></FONT> </DIV> <DIV><FONT size=2>Why would you not clamp epoxy?  The = bridge needs to be pulled back together, among other reasons, to get the pins = back in the right position.  My conversation this date with Roger = Weisensteiner confirmed my belief that this would be the method of choice = for making this repair.  He suggested using a two part epoxy (e.g. = West System type) and clamp it back together reinserting the pins either = before or after it dried.  My concern with after is that if I have = to redrill the case might be in the way.  So I will probably reinsert the = pins before it dries.</FONT></DIV></BLOCKQUOTE> <DIV dir=ltr><FONT color=#000080 size=2>Unlike nearly all other = adhesives, epoxy is an excellent gap filler. In fact, it actually requires a rather thick = glue line for best adhesive strength. Rather than say "don't clamp at all," I = would say clamp lightly--just enough to bring the crack just shy of fully closed. </FONT></DIV> <DIV dir=ltr><FONT color=#000080 size=2></FONT> </DIV> <DIV dir=ltr><FONT color=#000080 size=2>West System is a good = epoxy for this repair, but it should be used with some kind of filler to improve its = resistance to cold flowing--it is a plastic, after all. I would suggest a bit of micro-fiber (ground cotton fibers) to add strength and some colloidal = silica to add hardness. Try equal amounts of each, adding just enough to bring the = matrix up to the consistency of warm peanut butter.</FONT></DIV> <DIV dir=ltr><FONT color=#000080 size=2></FONT> </DIV> <DIV dir=ltr><FONT color=#000080 size=2>You'll want to insert the = pins before the epoxy hardens. And you'll want to clean up the excess and = squeeze-out before it all fully hardens as well. Things can get pretty difficult after the = whole mess gets hard.</FONT></DIV> <DIV dir=ltr><FONT color=#000080 size=2></FONT> </DIV> <DIV dir=ltr><FONT size=2></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV><FONT size=2>Regarding solvents and epoxy, I have, in the past, = repinned bridges putting a drop or two of epoxy in the bottom of the bridge pin = hole prior to inserting the pin.  The squeeze out I have cleaned up by = brushing it onto the notch using an acid brush with a bit of lacquer thinner.   I think I may have been introduced to this = technique by Bill Spurlock in a Journal article in fact.  Though I recognize = the controversy surrounding epoxying bridge pins in, I wasn't aware that a = bit of lacquer thinner was compromising the strength of the epoxy.  </FONT></DIV></BLOCKQUOTE> <DIV dir=ltr><FONT color=#000080 size=2>Joe was referring to the = practice of adding a thinner such as lacquer thinner to the epoxy to thin it out and = get it to flow into the cracks more readily. It is true that you can thin epoxy = in this manner, but it does chemically weaken the material and introduces a = certain amount of shrinkage as the thinner flashes out of the mixture. It is = doubtful that you will get enough thinner into the epoxy mix using it as you describe.</FONT></DIV> <DIV dir=ltr><FONT color=#000080 size=2></FONT> </DIV> <DIV dir=ltr><FONT color=#000080 size=2>Incidentally, epoxy cures = chemically, it does not "dry. It is this property that keeps it from shrinking as it = sets up. There is no--or at least, very little--solvent to flash = out.</FONT></DIV> <DIV dir=ltr><FONT color=#000080 size=2></FONT> </DIV> <DIV dir=ltr><FONT color=#000080 size=2>Regards,</FONT></DIV> <DIV dir=ltr><FONT color=#000080 size=2></FONT> </DIV> <DIV dir=ltr><FONT color=#000080 size=2>Del</FONT></DIV> <DIV dir=ltr><FONT color=#000080></FONT> </DIV></BODY></HTML>