Everyone likes to talk about how a good glue joint is stronger than the
wood itself. I think this may be true in a very technical sense, but
absolutely false in practice.

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

Conversely, the solid 10" wide piece of oak will certainly withstand a
harder blow without breaking than would the glue-up panel.

What am I missing in this 'glue is stronger than the wood itself'
argument?

How about if you glued two 2.5" oak boards to either side of a 5" oak
board and wacked it with a sledgehammer? Would it still break along
one or both of the glue lines or right in the middle of the glued up
10" board?

Dave

"Chuck" wrote in message
oups.com...
Everyone likes to talk about how a good glue joint is stronger than the
wood itself. I think this may be true in a very technical sense, but
absolutely false in practice.

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

Conversely, the solid 10" wide piece of oak will certainly withstand a
harder blow without breaking than would the glue-up panel.

What am I missing in this 'glue is stronger than the wood itself'
argument?


http://www.newwoodworker.com/useglue.html for a non-chemical discussion of
glue joints. Fact of the matter is that even in your example, while not
absolute, a properly done glue joint is likely to be stronger than the wood
itself. Even oak. (Although I'd suspect that a hardwood like oak would
certainly test the limits of the theory.)

Does seem strange, doesn't it?

James...

On 1 Jun 2005 11:37:01 -0700, "Chuck" wrote:

Everyone likes to talk about how a good glue joint is stronger than the
wood itself. I think this may be true in a very technical sense, but
absolutely false in practice.

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

I think Chuck just propped up a tar baby, but I'll take a poke at it
anyway. If "it takes a little wood from either side" doesn't that
mean that the glue is stronger than at least the part that it was
taken from?

In article .com, "Chuck" wrote:
Everyone likes to talk about how a good glue joint is stronger than the
wood itself. I think this may be true in a very technical sense, but
absolutely false in practice.

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

Try it. You may be in for a surprise.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

I'm guessing you haven't actually attempted the experiment. :-)

Conversely, the solid 10" wide piece of oak will certainly withstand a
harder blow without breaking than would the glue-up panel.

What am I missing in this 'glue is stronger than the wood itself'
argument?

Real-world experience.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

That's what I meant by being technically stronger, but not stronger in
practice. If the glued-up panel breaks with less force than the solid
wood panel, then the glued up panel is weaker. Whether it breaks clean
on the glue line, or takes a little wood with it is irrelevant.

"Chuck" wrote in message
oups.com...
Everyone likes to talk about how a good glue joint is stronger than the
wood itself. I think this may be true in a very technical sense, but
absolutely false in practice.

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

Conversely, the solid 10" wide piece of oak will certainly withstand a
harder blow without breaking than would the glue-up panel.

What am I missing in this 'glue is stronger than the wood itself'
argument?


Nothing. Glue is not stronger than the wood. It does, however, seem to bond
cellulose stronger than lignin.

Oh yes, your example depends a lot on the orientation of the growth rings.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

The glue joint is an irregularity, and if you wack it hard enough to break
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.

Chuck wrote:
That's what I meant by being technically stronger, but not stronger in
practice. If the glued-up panel breaks with less force than the solid
wood panel, then the glued up panel is weaker. Whether it breaks clean
on the glue line, or takes a little wood with it is irrelevant.

I guess it depends on what you mean by "a little wood".

If it takes 1/8" all the way down on either side of the glue line, I
would say the glue like is stronger than the wood itself.

Chuck wrote:
That's what I meant by being technically stronger, but not stronger in
practice. If the glued-up panel breaks with less force than the solid
wood panel, then the glued up panel is weaker. Whether it breaks clean
on the glue line, or takes a little wood with it is irrelevant.

I guess it depends on what you mean by "a little wood".

If it takes 1/8" all the way down on either side of the glue line, I
would say the glue line is stronger than the wood itself.

On 1 Jun 2005 11:37:01 -0700, "Chuck" wrote:

Everyone likes to talk about how a good glue joint is stronger than the
wood itself. I think this may be true in a very technical sense, but
absolutely false in practice.

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

Conversely, the solid 10" wide piece of oak will certainly withstand a
harder blow without breaking than would the glue-up panel.

What am I missing in this 'glue is stronger than the wood itself'
argument?

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.

Bill

On 1 Jun 2005 11:37:01 -0700, "Chuck" wrote:


What am I missing in this 'glue is stronger than the wood itself'
argument?

It's a matter of adhesion: Glue-wood, or wood-wood.

A simple test: Drop some glue directly onto some wood. Let it dry
hard. Try to remove the glue without taking along some wood.

On 1 Jun 2005 12:43:03 -0700, "Chuck" wrote:

Whether it breaks clean
on the glue line, or takes a little wood with it is irrelevant.

No it's not. It's the key, as I already suggested in another post.
If it takes wood with it, then the break is wood-wood. If the
glue-wood bond isn't stronger, it will break away from the wood. That
is the glue and wood will separate, or the glue itself will separate,
with some still adhering to both bits of wood. Try using a *much*
lighter glue for example, or bashing itbefroe the glue has completely
set, but is adhering. The parts will separate easily at the joint.
In fact, this is the reason for failure of some joints.

"Chuck" wrote in message
oups.com...
..

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

Conversely, the solid 10" wide piece of oak will certainly withstand a
harder blow without breaking than would the glue-up panel.

What am I missing in this 'glue is stronger than the wood itself'
argument?

Reread what you declared in your findings, "It may take a little wood from
either side of the joint," think about it a bit and you will realize that
the glue is stronger than the wood.

"Chuck" wrote in message
oups.com...

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

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.

--
********
Bill Pounds
http://www.billpounds.com

"Chuck" wrote in message
ups.com...
That's what I meant by being technically stronger, but not stronger in
practice. If the glued-up panel breaks with less force than the solid
wood panel, then the glued up panel is weaker. Whether it breaks clean
on the glue line, or takes a little wood with it is irrelevant.


NOW you are changing the whole story. In your title you indicate that glue
is not stronger than wood. NO ONE has said that glue makes a panel
stronger. Most everyone knows that a glued up panel will not break and
leave exposed glue, wood is always exposed. Hence the glue is stronger than
the wood.

wrote in message
...
snip


Of a few
dozen practice breaks, only one board broke on the glued joint,
leaving "a little wood on either side".

Umm if a little wood was left on either side of the glued joint, the joint
did not break. I simply broke near the joint. Unless you saw glue down one
edge, the wood broke.

"toller" wrote in message
...

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

The glue joint is an irregularity, and if you wack it hard enough to break
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.

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
will not.

wrote:

How about if you glued two 2.5" oak boards to either side of a 5" oak
board and wacked it with a sledgehammer? Would it still break along
one or both of the glue lines or right in the middle of the glued up
10" board?

Bingo--it breaks in the middle because that's the point of maximum stress.
If the OP put the glue line in the middle on his test specimens then he did
not consider all the possible variables.

Dave

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

Chuck wrote:
That's what I meant by being technically stronger, but not stronger in
practice. If the glued-up panel breaks with less force than the solid
wood panel, then the glued up panel is weaker.

Does it? Have you tried? I haven't but I pretty much doubt it, never
had a glue joint break.

--
dadiOH
____________________________

dadiOH's dandies v3.06...
....a help file of info about MP3s, recording from
LP/cassette and tips & tricks on this and that.
Get it at http://mysite.verizon.net/xico

On 1 Jun 2005 11:37:01 -0700, "Chuck" wrote:

Everyone likes to talk about how a good glue joint is stronger than the
wood itself. I think this may be true in a very technical sense, but
absolutely false in practice.

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

Conversely, the solid 10" wide piece of oak will certainly withstand a
harder blow without breaking than would the glue-up panel.

What am I missing in this 'glue is stronger than the wood itself'
argument?

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

skeez

On 1 Jun 2005 12:43:03 -0700, "Chuck" wrote:

That's what I meant by being technically stronger, but not stronger in
practice. If the glued-up panel breaks with less force than the solid
wood panel, then the glued up panel is weaker. Whether it breaks clean
on the glue line, or takes a little wood with it is irrelevant.

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

SNIP

What am I missing in this 'glue is stronger than the wood itself'
argument?


SNIP

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

Chuck wrote:

That's what I meant by being technically stronger, but not stronger in
practice. If the glued-up panel breaks with less force than the solid
wood panel, then the glued up panel is weaker. Whether it breaks clean
on the glue line, or takes a little wood with it is irrelevant.

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?

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

Dave

loutent wrote:



Besides, Norm sez the glue joint is stronger - good 'nough
for me and my stuff.

Lou

On Wed, 01 Jun 2005 20:58:25 -0400, loutent wrote:

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

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

"Leon" wrote in message
news

"toller" wrote in message
...

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

The glue joint is an irregularity, and if you wack it hard enough to
break 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.

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 will not.
You may have heard everything, but evidently you have tried nothing. Break
some glued up panels. 90% will be just off the glueline.

wrote in message
...
On 1 Jun 2005 11:37:01 -0700, "Chuck" wrote:

Everyone likes to talk about how a good glue joint is stronger than the
wood itself. I think this may be true in a very technical sense, but
absolutely false in practice.

Take for example, a panel glue up with two 5" wide oak boards glued
edge to edge (no biscuits, etc). There is no way in the world that this
panel is stronger than a single 10" wide piece of oak.

If you whack the glued-up panel with a sledgehammer hard enough, it
will split along the glue line. It may take a little wood from either
side of the joint, but is will definitely break right along the joint.

Conversely, the solid 10" wide piece of oak will certainly withstand a
harder blow without breaking than would the glue-up panel.

What am I missing in this 'glue is stronger than the wood itself'
argument?

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.

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.

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.

"Chuck" wrote in message
ups.com...
That's what I meant by being technically stronger, but not stronger in
practice. If the glued-up panel breaks with less force than the solid
wood panel, then the glued up panel is weaker. Whether it breaks clean
on the glue line, or takes a little wood with it is irrelevant.

Chuck says...

What am I missing in this 'glue is stronger than the wood itself'
argument?

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.

But...if you actually have glued some wood along the
same grain, you wiould soon realize how strong that
glue joint is

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.

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.

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.

Subject

Bull ****.

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

In article .com,
"Chuck" wrote:

[snip]
What am I missing in this 'glue is stronger than the wood itself'
argument?

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 ****-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 **** 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.

On Thu, 02 Jun 2005 02:49:15 GMT, "toller" wrote:


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 will not.
You may have heard everything, but evidently you have tried nothing. Break
some glued up panels. 90% will be just off the glueline.

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!

"Phillip Hallam-Baker" wrote in message
oups.com...
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.

Give the lad a maple board, toughen him up a bit.


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

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

George says...

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

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

I vote for jatoba or Peruvian walnut.

In article , "toller" wrote:

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

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?

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

CW wrote:

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.


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.

On Wed, 01 Jun 2005 22:22:03 GMT, skeezics wrote:

On 1 Jun 2005 11:37:01 -0700, "Chuck" wrote:

What am I missing in this 'glue is stronger than the wood itself'
argument?

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

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

http://www.DouglassClan.com