Hey Guys, I hope this information is helpful. I have had week glue joints from epoxy in the past, and after a few test samples, I figured out what the problem was. First, a slow set epoxy is made to saturate the wood into the grain. I usually score the glue joint with an old broken saw blade, then brush both sides with epoxy. My epoxy is pumped into dixie cups, mixed, and allowed to stand 5 min. before I spread it. If you clamp too tightly, it will not affect the strength of the glue joint AS LONG AS you allow the glue to saturate first... I recommend 15 minutes. I say this because I use it all the time in the vac. press, which applies excessive pressure... much higher than possible with clamps. Most of the epoxy evacuates, leaving an invisible joint. In spite of all of the careful glue-ups, I had a joint failure 2 years ago that cost me $700 dollars. I had glued up a curved chair rail, and the joint cured 24hrs in the press, sat 2weeks no problem, then I noticed a seperation at the start. I put a screwdriver into the seperation and could not further it much. It was perfectly strong! I left the screwdriver in over night. the next day, the joint seperated 2' past the screwdriver! I called the MFG (not west system.... but greer.) As a rule of thumb, 1 to 1 epoxies are the strongest because they maintain some flexibility. 2-1 mixes are more commonly "coating" glues... ie veneering, surface finish, boat fiberglassing...... the durometer hardness of the 2-1 makes it weak under stress, and over time the super hard joint (which is brittle like glass) will simply seperate. THE FIX! because the epoxy is chemically the same as the 1-1, you can put the 1-1 mix into the joint and the re-glue will work very very well. West system is also a "blushing" epoxy, putting off "water" .... it needs to be sanded a little prior to re-glue. I hope this was helpful. Good Luck. Mark Perry www.carvedpianoparts.com > Date: Fri, 12 Nov 2010 12:18:41 +0800 > From: justpianos at our.net.au > To: pianotech at ptg.org > Subject: Re: [pianotech] epoxy problems - was green piano > > Ron, > Clamping too tightly can also lead to a weak joint. > > > > > > > > > > ************************************************************************* > > Just curious Ron, did you use West System epoxy? Did you use fillers? > > If so, what kind? How did you measure your 5:1 mixing ratio? I don't > > like the pumps at all for measuring. I always use a good scale. And in > > the case of mixing up smaller batches, it becomes more and more > > mandatory to measure with a good scale. Temperature can also be an > > issue - was it cold? > > *************************************************************************** > > > > I'll look at work tomorrow (yes, I'm finally back, but still working on > > getting > > benefits restored...) I'm pretty sure it was West System, no fillers, temp > > around 70ish. Left it overnight to cure. I'm sure there was user error; > > though > > I do remember getting out the little digital scale and trying to do it > > right ;-) > > > > Knowing me, I probably did a 1:1 mix.... > > > > Ron Koval > > chicagoland > > > > > > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20101112/a236faa4/attachment.htm>
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