I don't imagine you've tried it either.... Glue up a test panel eight inches
wide, out of *three* pieces, two 2" wide and one 4" wide, with the 4" piece in
the center. Support it at the edges, and step on it. Where does it break?
Doug Miller (alphageek at milmac dot com)
A real world application:
My son took Tai Kwan Do a few years back and had to break 1x10 pine
boards with various parts of his body. Breaking practice soon became
expensive, so I decided to re-cut the wider portions of the boards and
edge glue them together with Elmer's carpenter's glue. I clamped them
firmly over night and let them set for a couple of days. Of a few
dozen practice breaks, only one board broke on the glued joint,
leaving "a little wood on either side". All of the other boards broke
somewhere other than the glued joint.
Give the lad a maple board, toughen him up a bit.
Of course to really give 'em a challenge take a 1" thick piece of
polycarbonate (also known as bullet-proof 'glass') and veneer each face
with pine so they can't tell the difference.
You bring any pair of boards except white oak, and yes that includes
oily teak, any time and I will glue them with some epoxy filled with
You will leave your gonads on the deck trying to break that joint.
For white oak, same as above except resorcinol glue.
Instead of two 5" wide boards, glue up a 3" board and an 7" board. Then
whack it with your sledge. I THINK you will find it still splits down the
middle, not on the glue line.
Interesting discussion you started....
But...if you actually have glued some wood along the
same grain, you wiould soon realize how strong that
glue joint is
How strong? Strong enough for furniture etc - that's
about all we need.
Besides, Norm sez the glue joint is stronger - good 'nough
for me and my stuff.
OK so the cannonical test for this question would be to take a series
of 8/4 10" boards taken from the same tree, resaw them so that you have
pairs of boards that are as near to being identical as possible, then
rip one board from each pair at varying distances from the edge ranging
from (say) 1" through to 5" (the middle).
Then test breaking resistance under both static and dynamic loads
according to a range of configurations.
I suspect however that the test is still not testing the failure mode
that most of us see which is a board that has split due to the wood
shrinking but being unable to move for some reason. Boards glued in
this fashion using pre 1960s glues will most definitely have a tendency
to fail along the glue line, the glues of that era are nowhere near the
quality of modern glues.
On 1 Jun 2005 22:21:59 -0700, "Phillip Hallam-Baker"
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"
You're missing the fact that in addition to a glue joint in a glued
panel, there is also a break in the continuity of the grain. In other
words, a 12" wide flatsawn one piece board doesn't have a single line of
grain going the length of the board perpendicular to the face. A
perfectly quarter sawn board would have grain running the length of the
board and perpendicular to the face, and in that case it would break in
the same way as the glued panel. So I guess you could say the glue
joint is stronger than the wood, but it isn't as simple as that, because
wood is stronger in some directions than others. If instead of making
glued panels from butt joints you used a scarf joint, it would be a
different ball game.
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