Hide glue, which has been around a *long* time, is still stronger than the wood if the joint is prepared well and it hasn't been exposed to either moisture or excessive heat.
-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"
Tim Douglass
It sounds like you tested a glue joint that was not joined properly. I've never had a properly glued up panel break at the glue line when tested.
If glue is stronger than wood and the break is along a wood-wood line, then why use biscuits or dowels? If anything they would be most needed anywhere but the glue line...
Consider the real-world mechanics of gluing two long strips of wood, long edge to long end. Even the most minor of variations in thickness, or very minor twisting will make the glue joint very hard to get perfect flat, even with clamps. Both dowels and biscuits will allow aligning the flat, wide surfaces, much better.
Maybe because they are used to help insure _alignment_ of the joint, not primarily to strengthen it? do you suppose? just maybe? *snort*
The strongest glue joints are long grain to long grain, but not all joints are long grain to long grain.
Have you tried it??
I've tried this at least three times. Everytime the glue line was left intact. However, a end-to-end grain is very weak.
Take some scraps and try it yourself. Allow the glue to cure for 2 days before swinging the sledge hammer. You'll become a believer.
I guess I live in a more practical world. If I am designing a project that is going to be subjected to this kind of stress, use plywood! The strength difference between a solid and a glued up board would be so close, either could fail. Why take the chance? Who designes a project that close to failure points?
Dennis
Dennis
I guess I live in a more practical world. If I am designing a project that is going to be subjected to this kind of stress, use plywood! The strength difference between a solid and a glued up board would be so close, either could fail. Why take the chance? Who designes a project that close to failure points?
Dennis
Umm because the glue line is STRONGER than the WOOD. Use biscuits for butt joints or mitered joints where the end grain of the wood is going to pull out of the end of the board.
Well, Chuck, if you were out trolling, you got quite a catch.
If that's a serious statement though, you should realize that you're talking about two different questions:
1) Is the GLUE JOINT stronger than the wood itself? 2) Is a glued panel stronger than a solid panel of the same size?I have no doubt that the answer to (1) is Yes. Saw it for the first time in junior high shop class, and I've seen it several times since, even on smaller pieces. It always breaks the wood, not in the glue line.
The answer to (2) may very well be No, that is, a glued panel probably is weaker. But I think that has more to do with stress concentrations than the glue joint being weak. It's been a while since engineering school, so I might not do an adequate job of explaining, but I definitely remember the idea of stress risers. With any material under stress, discontinuities in the material create higher concentrations of stress around them. Think of sharp inside corners on rotating shafts, things like that. Why do you think corners are radiused on a crankshaft? It reduces the stress riser. The stress at the discontinuity is going to be higher than the nominal stress in the part.
I'd suggest that's exactly what's happening to a glued panel. The local stress is probably stronger around the glue line. (And that's what most people see is that the break happens near the glue line). A panel that is one solid piece doesn't have the higher localized stresses. (Except maybe around knots and things of that sort. But knots don't run the length of the panel).
Anyway, question (2) is pretty much academic, since most of us don't have access to boards wide enough to make a tabletop from one piece.
Greetings and Salutations...
On Thu, 02 Jun 2005 05:17:35 -0500, Prometheus wrote:
You kids with your glue...you are LUCKY to have glue. When I was a boy, we only had snail slime to hold the wood together....and that on a good day! And we had to walk 10 miles, through the snow...barefoot...to get to the shop to scrape the wood flat with our fingernails... Now...as for the strength issue...It's a non-issue for me. If it is a structural issue, then, one needs to use plywood, or something that will provide a panel of appropriate side and strength without the need of joints. If it is to get a good-looking raised panel for a door, that is NOT structural, but, DOES require that the glue joint be cut VERY ACCURATELY. Some folks advocate a slight cup to the joint, so the ends get crushed together "to keep gaps from opening up". I advocate making the glue line as straight as a laser line on BOTH boards. My goal is to joint them so that when I lay the pieces down on the saw table, and push them together, the joint closes up and disappears. The fact of the matter IS that glue is "stronger" than wood, and, that a well done glue joint WILL hold enough that the wood will split next to it. However, far too many glue joints are poorly done - they are starved for glue, or, cut with such gaps that the glue is acting as a filler, or, (As with a chair seat I repaired a while ago) the glue surface has been sealed with finish BEFORE glueing...keeping the glue from penetrating properly. A bad glue joint is MUCH weaker than wood...and indeed, will split first. Regards Dave Mundt
You worked inside a building? We used a clearing in the woods at the top of a hill where the snow lasted 10 months of the year.
Was it up hill both to and from the clearing?
Barry
Might be a bit harder to fool the kid into thinking those were pine.
Never mind that shit. How many rivers did you have to swim?
Those bone tools were a bitch to maintain an edge on, too.
You had feet?
You had woods?
Yeah. I remember when that guy came up with flaked flint. Man, what an improvement that was.
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