MW is correct.




Michael Williams wrote:

Hmmm. I don't think you have this quite right. According to your
description, why wouldn't the water just be forced out of the gap?

The sheets are held together because of the surface tension of the laminar
fluid layer. Pulling the sheets apart would seriously increase the free
surface area of the fluid which surface tension seeks to minimize. I think
it is pretty clear that this has nothing to do with the bonding in glue
joints, since, after all, the glue in short order ceases to be a fluid.
Cohesion (- surface tension) is important, but adhesion is the key.
Roughing the surfaces, as most glue manufacturers recommend, exploits this
aspect. However, glue films should be thin, just not too thin. Have you
ever been impressed by the strength of a cured gob of glue?

However, it is far to easy to over-generalize when speaking of glue.

-mw


On 6/30/04 1:37 PM, in article
.net, "Agki Strodon"
wrote:


"Leon" wrote in message
news
"Agki Strodon" wrote in message

news:aKqEc.2199

But that's a different physical phenomenon.

Is it? The water like glue displaces the air that is between the 2
surfaces. If there is a spot in a glued up joint that has an air space,

the

joint is week at that point


I don't want to be seen as a pedantic jerk by you chaps even though my
students often called me one but:

Glass sheets are held together by water between them because the water has
driven out the air and occupies the space between the two sheets. The
sheets themselves are then forced together (and against the water lamina) by
the air pressure that pushes them together at about 14 lb/sq in. The only
mediating pressure is the very slight air pressure on the thin lamina of
water between the sheets of glass that forces the water to push outward
against the sheets by pushing inward on the water. Surface tension has not
much to do with it unless there is an interactive attractive force in the
glass (or whatever) that pulls the water molecules toward the sheet but this
would be very slight in almost all cases of materials. Air pressure is the
force both holding the sheets together and, to an extremely small degree,
pushing them apart by pushing on the water lamina. If the glass sheets are
uniformly flat and measure, say 10"x10", each sheet is 100 sq in. The air
pressure produces 14 lb/sq in on each sheet so the total is [14 lb/sq in x
100 sq in/sheet x 2 sheets] - [the pressure on the water from the sides], or
2800 lb. (I ignored the very very slight pressure on the water lamina
because it close to zero). 2800 pounds is the amount of force needed to
separate the sheets if there's no other factor. We don't need that much
because when we slide the sheets over each other we reduce the amount of air
pressure push against them at the places where they are together. Finally,
by sliding the sheets enough, the holding pressure is reduced to an easy
force to apply.

Glues work differently and don't depend on air pressure to hold things
together. There are essentially two aspects, the adhesion of the glue to
the surfaces and the internal bonding strength between the molecules that
make up the glue itself. The solvent for the glue (water, alcohol,
whatever) is just a carrier. The glue dries by losing its carrier and (in
some cases) the chemical nature of the glue itself changes when that
happens. When it dries, it bonds to the things being glued and internally
inside the dab of glue between them. In the old days, both these bonds were
relatively weak and either the glue's internal bonds broke or the bond with
the material broke. Some glues produce bonds to materials that are stronger
than the material itself is internally AND the internal glue intermolecular
strength is also stronger.

Spaces in glued up joints produce weakness because theres no glue in the
spaces to form a bond.

Agkistrodon

Wally Goffeney wrote:

On Tue, 29 Jun 2004 16:38:05 -0400, Nova
wrote:

toller wrote:

The Garrett -Wade catalog has a PVA glue that it claims:
1) It fills gaps with strength
2) Squeeze out does not penetrate the wood and easily chips off when
dried, no need for scrapping.

I wonder how it holds a joint together if it "does not penetrate the wood
and easily chips off when dried"?

When fresh glue is directly applied to a surface it has maximum
ability to 'wet out' the surface and achieve optimum adhesion.
Adhesion will normally be a combination of chemical and mechanical
properties.

Squeeze-out will never yield optimum wetting and therefore adhesion.
The fact that squeeze-out doesn't penetrate the wood and easily chips
off when dried doesn't really tell you much about the adhesives
properties where properly applied.
Wally Goffeney
http://mywebpages.comcast.net/wgoffeney/index.htm

Are there any independent test results on this stuff?

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

"Eddie Munster" wrote in message
news
MW is correct.




Michael Williams wrote:

Hmmm. I don't think you have this quite right. According to your
description, why wouldn't the water just be forced out of the gap?

I'm not getting this right, I don't think but if you are asking why water
between the two sheets of glass doesn't just run out, here's why:

Three reasons are most important.

First, the intermolecular attraction between the positive hydrogen atoms in
the polar water molecules and the negative oxygen atoms in the polar silicon
dioxide molecules of the glass is greater than that between the water
molecules themselves. This results in the "wetting" of the glass and the
disappearance of the water's surface. The interaction keeps the water in
place on the glass.

Second, there is air pressure at the edges of the glass pushing against the
very thin water surface that occurs between the pieces of glass. Since the
pressure is the same all around the resultant is a force pushing the water
towards the center of the glass. It doesn't go there because of the
considerations of "wetting" (as discussed above) pulling the water and
forcing its dispersal over all the glass surfaces.

Third, there is also a thin surface of water at the edges of the water
lamina forming a concave meniscus. This is the only place where surface
tension exists in the system because it's the only water surface, there
being no water surface inside the lamina. This is also a result of the
first reason above.

Agkistrodon

"Leon" wrote in message
...

"Agki Strodon" wrote in message
link.net...

If I do some sexperiments, would anyone want the results?
How would you design the set of experiments? I'll do them this
weekend.

I believe the glue companies already have this data. IIRC their
recommendation is a smooth surface.

I checked several maufacturers and other sites and found it about equally
divided between smooth and roughed up. Who knows? I did not find any raw
or reduced data but didn't look that hard.

Agkistrodon

"Michael Williams" wrote in message
...
Hmmm. I don't think you have this quite right. According to your
description, why wouldn't the water just be forced out of the gap?

The sheets are held together because of the surface tension of the laminar
fluid layer.

There is NO surface tension inside the fluid layer. There cannot be because
there is no surface inside the water layer. The water wets the glass and
the interactions occur between water and glass molecules. Surface tension
occurs only at the edges of the lamina because surface tension is defined as
the intermolecular attraction between the molecules of the fluid at the
boundary of the fluid. Surface tension works against wetting and the
superiority of the SiO2 - H2O interaction over the H2O - H20 interaction
accounts for the wetting of the glass. If you smear paraffin on the glass
and then put water on it, the water will bead up and retain surfaces (and
surface tension) because the water-water attractive forces are greater than
the water-paraffin attractive forces.

Pulling the sheets apart would seriously increase the free
surface area of the fluid which surface tension seeks to minimize.

To the force of air pressure holding the plates together, we can add the
resultant force of all them damned SiO2 - H20 attractions. I think, though,
that it's rather small compared to the air pressure. We could set up an
apparaturs to measure it.

I think
it is pretty clear that this has nothing to do with the bonding in glue
joints, since, after all, the glue in short order ceases to be a fluid.

Absolute agreement.

Cohesion (- surface tension) is important, but adhesion is the key.
Roughing the surfaces, as most glue manufacturers recommend, exploits this
aspect. However, glue films should be thin, just not too thin. Have you
ever been impressed by the strength of a cured gob of glue?

However, it is far to easy to over-generalize when speaking of glue.

-mw

Quite so! Now for the biggest question in physics - one that Feynman and
the physics faculty at Cal Tech could not answer- why does a stick of
spaghetti almost always break into three or more pieces when you bend it by
the ends?

Agkistrodon

Does that mean that if you used something that wouldn't boil away, such
as silicone, the two pieces of glass would not stick together in a
vacuum? Has it been tried?


If the silicone molecules inter-attract with the silicon dioxide molecules
more strongly than they intra-attract amongst themselves, no. The plates
would stick through wetting of the glass. They may be easy to separate and
that is a way of finding the strength of the interactions.

As to whether anyone has done it, I dunno.

Agkistrodon

Agki Strodon wrote:
"Leon" wrote in message
news

"Agki Strodon" wrote in message
news:aKqEc.2199

But that's a different physical phenomenon.

Is it? The water like glue displaces the air that is between the 2
surfaces. If there is a spot in a glued up joint that has an air space,
the
joint is week at that point


I don't want to be seen as a pedantic jerk by you chaps even though my
students often called me one but:

Glass sheets are held together by water between them because the water has
driven out the air and occupies the space between the two sheets. The
sheets themselves are then forced together (and against the water lamina) by
the air pressure that pushes them together at about 14 lb/sq in. The only
mediating pressure is the very slight air pressure on the thin lamina of
water between the sheets of glass that forces the water to push outward
against the sheets by pushing inward on the water. Surface tension has not
much to do with it unless there is an interactive attractive force in the
glass (or whatever) that pulls the water molecules toward the sheet but this
would be very slight in almost all cases of materials. Air pressure is the
force both holding the sheets together and, to an extremely small degree,
pushing them apart by pushing on the water lamina. If the glass sheets are
uniformly flat and measure, say 10"x10", each sheet is 100 sq in. The air
pressure produces 14 lb/sq in on each sheet so the total is [14 lb/sq in x
100 sq in/sheet x 2 sheets] - [the pressure on the water from the sides], or
2800 lb. (I ignored the very very slight pressure on the water lamina
because it close to zero). 2800 pounds is the amount of force needed to
separate the sheets if there's no other factor. We don't need that much
because when we slide the sheets over each other we reduce the amount of air
pressure push against them at the places where they are together. Finally,
by sliding the sheets enough, the holding pressure is reduced to an easy
force to apply.

Glues work differently and don't depend on air pressure to hold things
together. There are essentially two aspects, the adhesion of the glue to
the surfaces and the internal bonding strength between the molecules that
make up the glue itself. The solvent for the glue (water, alcohol,
whatever) is just a carrier. The glue dries by losing its carrier and (in
some cases) the chemical nature of the glue itself changes when that
happens. When it dries, it bonds to the things being glued and internally
inside the dab of glue between them. In the old days, both these bonds were
relatively weak and either the glue's internal bonds broke or the bond with
the material broke. Some glues produce bonds to materials that are stronger
than the material itself is internally AND the internal glue intermolecular
strength is also stronger.

Spaces in glued up joints produce weakness because theres no glue in the
spaces to form a bond.

Agkistrodon


Does that mean that if you used something that wouldn't boil away, such
as silicone, the two pieces of glass would not stick together in a
vacuum? Has it been tried?

--

Gerald Ross, Cochran, GA
To reply add the numerals "13" before the "at"
............................................
People will die this year that never
died before.




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On Thu, 01 Jul 2004 18:29:00 GMT, "Agki Strodon"
calmly ranted:

Quite so! Now for the biggest question in physics - one that Feynman and
the physics faculty at Cal Tech could not answer- why does a stick of
spaghetti almost always break into three or more pieces when you bend it by
the ends?

I'm sure he knew that it was the harmonic vibrations of the
first 'snap' which multiplied in the pieces and facilitated
further breaks. /swag


------------------------------------------------------------
California's 4 Seasons: Fire, Flood, Drought, & Earthquake
--------------------------------------
http://www.diversify.com NoteSHADES(tm) glare guards

"Larry Jaques" wrote in message ...
On Thu, 01 Jul 2004 18:29:00 GMT, "Agki Strodon"
calmly ranted:

Quite so! Now for the biggest question in physics - one that Feynman and
the physics faculty at Cal Tech could not answer- why does a stick of
spaghetti almost always break into three or more pieces when you bend it
by
the ends?

I'm sure he knew that it was the harmonic vibrations of the
first 'snap' which multiplied in the pieces and facilitated
further breaks. /swag

Hmmm, interesting. My guess partially agrees with Lar. I'd say the harmonic
from the initial break travels down the remaining stick until it reaches the
second flex point. When the harmonic and the flex point meet, the spaghetti
breaks.

Now, just how *do* brass screws permanently disappear in sawdust? Why is it
so?

Groggy

They're attracted to pencils by the fifth force, the one that also causes
socks to fly out of the dryer.

"Greg Millen" wrote in message
s.com...

Now, just how *do* brass screws permanently disappear in sawdust? Why is
it
so?

Groggy

This phenomenon works with oils to. Or no fluids. and not using glass
but any very flat surfaces. I would suspect if you reduced the air
pressure in a chamber and measured the pll away forces of the two
plates, nothing would change. Gosh it is even noticable at HD seperating
sheets of plywood. What are Johansson blocks?

John

Agki Strodon wrote:
"Eddie Munster" wrote in message
news
MW is correct.




Michael Williams wrote:


Hmmm. I don't think you have this quite right. According to your
description, why wouldn't the water just be forced out of the gap?


I'm not getting this right, I don't think but if you are asking why water
between the two sheets of glass doesn't just run out, here's why:

Three reasons are most important.

First, the intermolecular attraction between the positive hydrogen atoms in
the polar water molecules and the negative oxygen atoms in the polar silicon
dioxide molecules of the glass is greater than that between the water
molecules themselves. This results in the "wetting" of the glass and the
disappearance of the water's surface. The interaction keeps the water in
place on the glass.

Second, there is air pressure at the edges of the glass pushing against the
very thin water surface that occurs between the pieces of glass. Since the
pressure is the same all around the resultant is a force pushing the water
towards the center of the glass. It doesn't go there because of the
considerations of "wetting" (as discussed above) pulling the water and
forcing its dispersal over all the glass surfaces.

Third, there is also a thin surface of water at the edges of the water
lamina forming a concave meniscus. This is the only place where surface
tension exists in the system because it's the only water surface, there
being no water surface inside the lamina. This is also a result of the
first reason above.

Agkistrodon

"Agki Strodon" wrote in message hlink.net...
"Leon" wrote in message
m...

"Agki Strodon" wrote in message
news:4TCEc.20861$bs4.13057

Spaces in glued up joints produce weakness because theres no glue in the
spaces to form a bond.

Now you are showing signs that you might understand the point that I was
trying to make.

You said,

"A roughed up surface holds better than a smooth one because there's more
glue in the between pieces volume, ain't it?"

Roughed up surfaces often cause spaces in the glued up joint. A smooth
surface is Ideal for glue.



That is really debatable, mein Herr. It depends. If the glue can get into
the roughed up spaces, it will be stronger because there will be more glue
in the joint as a result of the increased surface area caused by the
roughening up.

I think it depends on how rough and what sort of glue. With most any
glue but epoxy the roughness must be small enough that you have a very
thin layer accross the interface. If you roughen the surface to the
point that the glue is filling gaps the result will be a weaker
joint than if you just planed the surfaces smooth and glued them
because the glue in the pockmarks will be weaker than the wood it
replaced. I dunno where you cross the line between giving the glue
tooth, and weakening the joint by requiring the glue to fill a gap.

I _think_ that a planed or scraped surface has the correct level
of roughness for most glues, and does not have as many loose fibers
or dust particles in the pores and does a surface roughened with
sandpaper.

With epoxies, the glue in gaps is stronger than the wood and the
strength can be maximized by eliminating the wood altogether, though
the resulting furniture may leave something to be esthetically desired.

--

FF

On Fri, 02 Jul 2004 09:09:07 GMT, "Greg Millen"
calmly ranted:

"Larry Jaques" wrote in message ...
On Thu, 01 Jul 2004 18:29:00 GMT, "Agki Strodon"
calmly ranted:

Quite so! Now for the biggest question in physics - one that Feynman and
the physics faculty at Cal Tech could not answer- why does a stick of
spaghetti almost always break into three or more pieces when you bend it
by
the ends?

I'm sure he knew that it was the harmonic vibrations of the
first 'snap' which multiplied in the pieces and facilitated
further breaks. /swag

Hmmm, interesting. My guess partially agrees with Lar. I'd say the harmonic
from the initial break travels down the remaining stick until it reaches the
second flex point. When the harmonic and the flex point meet, the spaghetti
breaks.

Now, just how *do* brass screws permanently disappear in sawdust? Why is it
so?

That, sir, is due to the scavenger elf (with his brass magnet) who
is hiding under all that sawdust and who absconds with them.

Nexxxxxt!

--
"Not always right, but never uncertain." --Heinlein
-=-=-
http://www.diversify.com Wondrous Website Design

On Wed, 30 Jun 2004 19:23:03 -0400, Michael Williams
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

Hmmm. I don't think you have this quite right. According to your
description, why wouldn't the water just be forced out of the gap?

The sheets are held together because of the surface tension of the laminar
fluid layer.

So the sheets would still stick together in a vacuum?

The surface tension of the ater is what stops the atmos pressure
forcing the water out from between the glass, perhaps.

On Wed, 30 Jun 2004 21:28:48 -0400, "Howard Ruttan"
wrote:

"Jay Pique" wrote ...
In the course of learning to work wood, I suppose it would do me good
to learn about adhesives. Any recommended tomes on the subject? I
don't need "all" the science, but I would like to see coverage similar
to that presented in Flexner or Jewitt's finishing books.

You don't really need a book if you read Chapter 9 of the Forest Products
Lab Handbook (link below). It outlines the properties of a properly
prepared surface and discusses, in detail, the fact that glue bonding is
almost entirely a mechanical process rather than a chemical one. It sounds
like several people in this thread may benefit from reading Chapter 9. You
can download it - FOR FREE (the best part)- right he
http://www.fpl.fs.fed.us/documnts/FP.../fplgtr113.htm

Thanks for the link - and the excellent discussion as presented by all
parties. This is the wreck at its best.

Happy 4th of July all of you USAmericans!

JP
***************
Going "golfing" of all things today.....ugh.

I must have missed the gist of the original post but here's some more
useless info...
If the glass plates are dead smooth, as in optical flats, and put together
with nothing in between, they will be forever joined in a short while. No
air space at all, there is a vacuum,, and the glass, an amorphous liquid,
yep liquid, will grow together by molecular migration. This also applies to
steel gage blocks as Johansen or Hoke blocks, but it takes a little longer
for them to become a unit. Been there, done that.... This has no parallel
to woodworking joint gaps, though...
As for wood, cleanly cut, flat, preferably planed and not sanded, wood bonds
better than rough wood any day.

Howie
Metrologist

"Agki Strodon" wrote in message
ink.net...
Does that mean that if you used something that wouldn't boil away, such
as silicone, the two pieces of glass would not stick together in a
vacuum? Has it been tried?


If the silicone molecules inter-attract with the silicon dioxide molecules
more strongly than they intra-attract amongst themselves, no. The plates
would stick through wetting of the glass. They may be easy to separate
and
that is a way of finding the strength of the interactions.

As to whether anyone has done it, I dunno.

Agkistrodon