How tight to clamp glue-ups?

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Ahh but you leave out the key comments. The thinner the glue layer the better the stronger the bond. The comment was made and as I have pointed out, that extra clamping pressure is only needed if the surfaaces do not touch evenly along the joint line. If you have flat mating surfaces, squeezing the glue tighter is not going to strengthen the glue.
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Leon wrote: ...

...
No, the effect of the extra gluing pressure contributes by helping in creating the thinner bonding layer as well as inducing (as the above alluded to as well) more integrated into the wood pores.
As noted above, these results have been verified over and over and over w/ identically prepared samples taking out the variable of the quality of the jointing surfaces, etc.
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If you put the proper amount of glue on in the first place there is no need to squeeze excess glue out. If you are working with flat mating surfaces and don't use excess glue there is no need to clamp except to keep the pieces properly aligned.

And for the last 30 years I have verified by my own practice that the joint is fine if properly set up to start with. Clamps are not necessary. Try this, put some glue on a "flat" scrap, and "lay" another flat piece of scrap on top, let set a few hours, see if you can break apart with out the wood actually failing.
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Leon wrote: ...

Again, that's the right answer to a different question...
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Actually I don't recall "you" asking a question. Did I miss your question?
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Leon wrote:

No, but there was lots of response to the OP's that I think wasn't quite right...addressing the difference between ultimate and "adequate" strength and effect of clamping pressure thereon.
I'm not disagreeing it's possible to get "adequate for most circumstances" glue strength w/ moderate to even minimal clamping force but otoh there is a relationship between clamping force and ultimate strength obtainable that seems worthy of being recognized...
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scrawled the following:

Isn't glue a pass/fail kind of situ? You either do it right and it survives punishment or you get it wrong and it fails catastrophically. Adequate = ultimate in this instance, wot?
-- No matter how cynical you are, it is impossible to keep up. --Lily Tomlin
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RE: Subject
When stuff stays stuck together where you want it after the clamps are taken off, the clamps were tight enough in the first place.
Lew
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Lew Hodgett wrote:

Again, right answer; different question...
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--------------------------------

---------------------------------
"dpb" wrote:

----------------------------------- No, right answer for the SUBJECT.
Different question requires different SUBJECT.
Lew
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Ahhh! My comments are backed up by Franklin!
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There is lots of practical info published on this for PVA glues (Titebond wood glue, etc.). FWW magazine had a study a while back. a few hundred lbs clamping force is what is needed. The most important things the study show is that various types of clamps have widely different capacities to generate clamping force. The modern parallel clamps can get to a thousand + pounds. Thin bar clamps can struggle to get to 150 lbs. Pipe clamps IIRC can also create quite some force. Strangely they report the pistol grip clamps also generate huge amounts of force but I just can't believe it. I just use them for positioning and lite work.
So use good clamps and there is no need to overtighten. Clamp until you see squeeze and give it another little twist just to be sure. Trust me, masking tape ain't gonna do it with PVA glue.
If you are edge gluing panels, you should envision a 90 degree V extending from the location of the clamp at the edge, 45 degrees on either side of centerline of the clamp bar. The V's of the clamps should overlap at the glue joint, so wider boards in the panel require fewer clamps becaus ethe V covers more area as it extends away from the face. I actually have some outer cauls I have been using lately that essentially widen the panels that give me the side benefit of needing less clamps sometimes.

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On 3/10/10 11:48 AM, SonomaProducts.com wrote:

Excellent description and practice.
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
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It has worked well for me... many hundreds of times, 24 times last week.

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On 3/10/2010 12:06 PM, -MIKE- wrote:

Belong to FWW online?
http://www.finewoodworking.com/fwnpdf/011194036.pdf
Page 40 ... worth the 14 day trial if you don't belong.
--
www.e-woodshop.net
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Ahh yes, that was the article I was thinking of. I forgot about the pressure over area calculation so my explaination was not complete.

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Yeah - I actually read that article once upon a time but then last night I was watching the weekly online version of New Yankee Workshop classics and Norm was talking about not clamping too tight to avoid squeezout... so I just wanted to get some additional perspective on these seemingly conflicting viewpoints...
I guess I tend to believe the science, but on the other hand real life doesn't always follow theory ;)
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blueman wrote:

I *like* squeeze out. A little bit, proves I used enough glue.
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dadiOH
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Precicely, and for those that like the "glue starvation" cautionary statement, it helps to indicate that there should be no glue starvation.
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Thanks to you and others for the very helpful explanation...
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