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
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
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.
the panel, it will probably break at the irregularity.
However, it will not break any easier than the solid panel.
The point of "the glue is stronger than the wood" pretty much means that
there is no advantage to using glue that is twice as strong, because the
glue is already as strong as possible.
Try your little experiment with epoxy; the result will be the same.
Now I have just about heard everything. The break is PROBABLY not going to
be at the joint. I may be very close to the joint but not at the joint.
Glue is stronger than wood means that the wood will break and the glue joint
Greetings and Salutations...
On Thu, 02 Jun 2005 05:17:35 -0500, Prometheus
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
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
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