202GF, A miracle glue?!

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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 4TCEc.20861$ snipped-for-privacy@newsread3.news.atl.earthlink.net, "Agki Strodon"

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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.
kiitos JP

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"Jay Pique" wrote ...

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 here: http://www.fpl.fs.fed.us/documnts/FPLGTR/fplgtr113/fplgtr113.htm
--
Cheers,
Howard
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On Wed, 30 Jun 2004 21:28:48 -0400, "Howard Ruttan"

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.
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Do any wood glue manufacturers recommend roughing the wood? The wood should be planed smooth to achieve the strongest joint.
--
Mac Cool

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Depends on the glue and the wood. Actually, I was thinking of non-porous materials when I wrote the quoted text--forgetting the context of the thread. Most wood glues work through 'wetting'-- the glue penetrates several cells deeply in the porous wood, forming mechanical (interlocking) (and also chemical) bonds. Thus smooth well mating surfaces are optimal as clamping then very effectively helps force the glue into the wood. A uniform thin layer is desirable. Machine and tool marks obviously diminish this and create distinct pockets.
With very dense, oily wood, porosity is minimal. The story is different. Epoxies do not depend on deep penetration and require different preparation. Slightly roughing the surface is sometimes desirable; see for example, <http://www.glen-l.com/supplies/pxman-use.html .
I think I will say no more having already fallen into the generalization trap. Mr Ruttan's suggested reference, <http://www.fpl.fs.fed.us/documnts/FPLGTR/fplgtr113/fplgtr113.htm is a good one indeed.
-mw
On 6/30/04 10:57 PM, in article Xns9518E983227A9MacCool@24.25.9.43, "Mac

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MW is correct.
Michael Williams wrote:

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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
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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:

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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.

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

Absolute agreement.

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

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
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"Larry Jaques" wrote in message ...

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

it
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calmly ranted:

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
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vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email

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.
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Agki Strodon wrote:

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
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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
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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

and
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Agki Strodon wrote:

As a general rule, a _clean_ surface holds better. Roughness doesn't improve bond strength with most adhesives and substrates and in many cases it weakens the bond.

--
--John
Reply to jclarke at ae tee tee global dot net
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No, a (slightly) roughened surface holds better than a smooth one because there is more surface area for the glue to bond to.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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