Glue is not stronger than wood.

[skeezics]

no argument exept that if you use NO glue it will surely break at the joint! lol :-]>

skeez

[Wes Stewart]

Dat Brer Fox he'd sho be de sly one.

[loutent]

Hi Chuck,

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.

Lou

[Duane Bozarth]

No. If the joint is well-prepared and a good quality glue is properly applied and cured (even PVA will work), the joint will rarely be what actually fails. A wide panel breaks more easily because there's a larger moment arm...actually, the appearance of "easier" is an illusion as the stress before the breaking point will be (within the variability of the wood itself) the same.

Have you actually done an experiment or just spouting?

[David]

Especially since he uses plenty of brads to hold the joint closed "until the glue sets".

Dave

loutent wrote:

[Guess who]

Anyhow, stronger or not, we DO need to glue. It's definitely weaker without.

[toller]

You may have heard everything, but evidently you have tried nothing. Break some glued up panels. 90% will be just off the glueline.

[toller]

My son also took TKD (even got his black belt, for whatever that must be worth). Those pine boards break if you look at them funny. I hope you use better wood in woodworking; the example is worthless.

[CW]

The glue joint is stronger. It is also less flexible. Stresses that would ordinarily fairly evenly spread over the board will concentrate in this hard spot.

[Hax Planx]

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.

[Phillip Hallam-Baker]

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.

[Phillip Hallam-Baker]

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.

[Lew Hodgett]

RE: Subject

Bull Shit.

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 some micro-balloons.

You will leave your gonads on the deck trying to break that joint.

For white oak, same as above except resorcinol glue.

Lew

[Robatoy]

[snip]

Guess Who (IF that's his real name) is right.

If the glue was 'less' strong than the wood, at the break, there would be glue on either side of the break. As that never happens (Unless it was a piss-poor job of clamping and setting of the joint.) there usually is failed wood on either side of the break, but never failed glue. So the glue wins every time, end of story.

"IF" total structural integrity of the glued joint is compromised in a solid piece of the same material (everything else being equal theoretically) it wouldn't be the fault of the adhesive, but because the original board has been "cut" discontinuing the structure, NOT because it was glued. IOW.. the failure was set to take place at the moment of cutting, not at the moment of breaking after the adhesion process.

Imagine, if you will, a glue line of 1/8" thick, fully cured Glue (insofar that is possible to obtain in shit like PVA, but we're being hypothetical here), attached on both sides to wood, then break that lamination, and I assure you, the wood would give up parts to the adhesive, and the adhesive would stay in one piece.

Test this theory on end grain particle board (Legal in this argument as it negates any unpredictability). You will find the break to be either on the left side of the joint or the right, but never in the exact middle, most of the time a jagged break with material on either side.

As a countertop guy, this kinds stuff is important to me and I have tested that with every glue I have ever bought, I hate to get stuck with a 5 gallon pail of stuff that doesn't work.

To help a lot in making the joint stronger, one would be smart to lengthen the glue line by using TruMatch or finger joints, in the hope to restore some of the continuation of the 'cut' fibrous or granular structure of the wood in question.

Rob

The moon is smaller than the earth even though it is further away.

[Prometheus]

Why are you guys so determined to bust up nicely glued panels? Make a little tabletop or something out of them, and be happy you had glue instead of baling wire or double-sided tape! :)

[George]

Support it at either end, and make hem break it across the grain.

Hell, have some fun and use some nice springy ash....

[Hax Planx]

I vote for jatoba or Peruvian walnut.

[Doug Miller]

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?

[Duane Bozarth]

I think that depends on both the specific wood and the specific glue...pva's, for instance, aren't very rigid. I don't have figures for modulus, though, but I suspect they're close, at best.

[Tim Douglass]

Not if you use enough biscuits!

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass