Testing a glue joint.....

Re: Testing a glue joint.....

TomD

The bridge on a classical guitar is held on with glue and is under a constant 100 poundish load, whether you play it or not. In modern times these are often held on with "white" glue, or the similar "yellow" glue. The preferred brand is Titebond 1, and I use it for all such uses as it has been the industry standard for many years. Hide glue works as well or better, and has made a strong comeback in lutherie in recent years. When I put on my bridges I just rub them in place, which is also how I made joints like the panel joints in the soundboards, or other things.

I have a 30 year old trimaran that I still sail, and it was structured by bending panels under great force that are held together by nothing other than a fillet of epoxy. It has to be a really hard brand like WEST. Sure it is epoxy, but it is just wood where the glue ends.

By the way, because of the potential longevity both in use and design, if one wants to actually test structures, or glues it is very important to be sure the test reflects the failure mode, which in the situations described would be creep. I am always suspicious of test on things like joints where they just destroy the joint in short order with a hammer or clamps. Also, on the flip side, some glue keep gaining creep resistance for months.

Re: Testing a glue joint.....

Barry Irby

My point was that the glue lasted fifty years and was still stronger than the wood. And it was plain old Elmer's white glue. Don't know if Titebond was on the market fifty years ago and did not see it in the small town I grew up in.

I had been wondering about the longevity of glue joints. I have repaired a number of antiques with joints that appeared to have aged out, the glue just crumbled. Probably hide glue. Even though two joints failed on the clock the rest were fine. The two that failed were probably affected by the cross grian stress from putting the front of the base on as a solid wood panel.

Re: Testing a glue joint.....

Brian Holcombe

I think a lot of age related failures were doomed from the start. Certain doweled connections, for instance, just don’t seem to survive well

Re: Testing a glue joint.....

Barry Irby

This one was. At least the front of the base was doomed because it is a panel about 16" wide with a cross piece right behind it and glued to it. If I knew then what I know now I would not have done it that way, but I was green and just followed the plan.

At the time I had very limited tools and did the whole thing with a radial arm saw and hand tools. The spline I used for the front panel joints was a piece of 1/4" fir plywood. Hmmm?