glue joints

[JasonB]

hey Don I got a question for ya!
it concerns glue joints. I have always had a problem with my joints "breaking" they don't actualy break but it gets to the point where you can feel the joint and the laquer actualy cracks along the joint. usualy this is on my jewelry boxes, along the trim around the lid. I have come to the conclusion that this is just a part of working with wood. what do you think? I have used woods of varying degrees of being cured from "fresh from the lumberyard" to 10-20 year old boards. and I typicaly use tightbond or tightbond2.:confused:

[Dagster]

I'm not Don but I do know that if glued properly the glue joint should be stonger than the wood itself. Something is wrong.

Do you have any pictures of the failures? Are you glueing long grain to long grain?

[Don]

Hey, Jason. Dagster probably hit the nail on the head with grain question. The other clue is that you mentioned lacquer. For the most part your conclusion is correct. Wood moves due to temperature and moisture content. Water vapor is a gas and can easily pass through many substances, wood finishes are one of them. If you use different species of wood on something like a decorative box, the woods don't move in concert with each other, their mass being different and reacting at different speeds to temp and humidity.

That being said, lacquer is not kind to this process at all. It is a very brittle material. Look at any old lacquer finished antique and you will find fractures at all joints, not enough to break the joint as you mention, but enough to break the finish at the line. That's why early mechanical joints in woodworking were so valuable, their glue sucked. Hide glues and the like were very brittle. The joints might "work" loose but not come apart because of dovetails, tenons, dowels, pins, nails.

Okay, how do we solve your problem? First I'd get away from lacquer. The only finish out there that I can attest that is not hydroscopic (will let water molecules pass) is epoxy. Modern epoxy is a joy to use, sands and builds well. It has some elastic qualities that may solve your problems of slight movement of parts. This is a good place to begin to learn about epoxies, http://www.systemthree.com/index_2.asp

Another alternative is to go to some of the oil and wax finishes that are available like, http://www.briwaxwoodcare.com/ they simply let the wood move, there is no film to fracture.

I doubt that your wood techniques are causing the problem. If you post some pictures of the specific occurrences then maybe me or some of the guys can point and say, "there's your problem."

All the best, Don