FWW's article on Glue-Ups Fact or Fiction?

[Carl Eyman]

Did anyone else have fear struck in their heart by FWW's article on how to glue up a panel. I've obviously been doing it all wrong for 40 years. I expect the next time I look at a panel I've done I'll be watching it come apart as I watch. I'm not arguing with the author, but I'm sure I've been using a lot less clamps and a lot less pressure than he recommends. Yet I look at panels every day and can't think of one that has failed.

What do the rest of you think?

The author's credentials are impressive; so I feel uncomfortable in questioning his conclusions. But . . .

[Alex Berkovsky]

Slightly OT, but what struck me was the fact that a Quick-Grip clamp was rated at 470lb, whereas a parallel jaw clamp was rated at 370lb.

[David G Baker]

I have never found that credentials are written in stone when it comes to things that I have experienced and work for me, but I am not beyond learning from someone else's expertise. If it makes sense maybe the author has a good point. If not, why change now?

[Carl Eyman]

Slightly OT, but what struck me was the fact that a Quick-Grip clamp was rated at 470lb, whereas a parallel jaw clamp was rated at 370lb.

I have to doubt him on this or he had a gorilla using the Quick Grip. When I've tried to bring a tight joint together with the Quick grip and failed a parallel jaw has worked.

[Howard Acheson]

Before we get to far afield, let me point out that the two manufacturers of PVA adhesive (Franklin and Borden) specify the clamp pressure quoted by the author. In addition, the USDA, Wood Products Laboratory in their Wood Handbook specify the same clamping pressure.

Also, a properly prepared joint will hold together with less pressure. But, for maximum strength and minimal glue line, the higher pressure is required.

[David Weaver]

He's probably correct about clamping pressure needed, but I find the ranking of the clamps kind of hard to believe.

You can bend bessey clamps - they have to be putting out more than 300 pounds of pressure when the bar is bending.

It seems better to spend the time making the joints right so you don't have to clamp the shizz out of them.

[Jamie Buxton]

Like you, Carl, I find that article does not ring true. PVA works just fine under far less pressure than he recommends. For instance, mortise and tenon joints generally don't get any pressure across the glue line, but they work. Wiped joints, too, work just fine in PVA, and they have zero applied pressure. In panel glue-up, I rarely use as many clamps as he recommends, but if I test the butt joint to failure, it is the wood that fails, not the glue.

[Gary Keedwell]

As I was reading that last nite, I almost choked when I seen how many clamps that guy was using. He said that you need so many that there wouldn't be enough room to put all the quik clamps.
I don't know though, about labels. If you read the label on finishing products, it tells you not to dilute the contents. What it doesn't tell you is that they took out the mineral spirits to comply with VOC laws. You have to actually thin your finishing products because they are too thick but they can't tell the consumer that information.:confused:
Gary

[josh bjork]

He's probably correct about clamping pressure needed, but I find the ranking of the clamps kind of hard to believe.

You can bend bessey clamps - they have to be putting out more than 300 pounds of pressure when the bar is bending.

It seems better to spend the time making the joints right so you don't have to clamp the shizz out of them.

Wouldn't the psi of clamps be tied to the surface area of the jaws? The big clamps have a ton more surface area available.

[Gary Keedwell]

Wouldn't the psi of clamps be tied to the surface area of the jaws? The big clamps have a ton more surface area available.
They are if you can get the torque. They said the "T" handle clamps gave the best torque.
GK

[David Weaver]

Wouldn't the psi of clamps be tied to the surface area of the jaws? The big clamps have a ton more surface area available.


I guess what I'm getting at is that I use parallel bar clamps for almost everything, and I think that when you can get a good grip on them, you can bend the bar some, even when the spread isn't that far.

The PSI at the joint shouldn't reflect the amount of surface area of the clamps - if they're clamping with 500 pounds of pressure, that's 500 pounds. I sure would worry about the wood fibers on a cherry panel using one of those iron bar clamps with 1500 psi of pressure. I'm assuming that you're saying that you can get a lot more clamping pressure at the same psi at the jaws of the clamp if you use the bessey style clamps.

I'm still a bit of a newbie, though - maybe it's more important if you're throwing things together straight off the table saw or machine jointer. I have never put a panel together without planing the edge until there is no light under a starret edge, aside from maybe a tiny fraction so that the straight edge pivots on the ends of the jointed board.

Production for the guys on here who do this for a living is, I guess, a far different thing.

[Dixon Peer]

Slightly OT, but what struck me was the fact that a Quick-Grip clamp was rated at 470lb, whereas a parallel jaw clamp was rated at 370lb.

Me too. That's really all I wanted to say, but the forum software apparently needed a longer message for some reason, so I'm writing more here

[Gary Keedwell]

I always make my panels a couple inches bigger then necessary and when I lay out the boards for the most pleasing face I check for light between the boards. I work the edges until all the boards are straight enough to go together by hand without any pressure.
Seems to me the straighter the board.....I never BEND the board with the clamps to make it straight. Does this post make any sense? LOL:p
Gary

[Oscar Mueller]

I build all kinds of custom wood pieces for a living.I use the Jorgensen 72 steel bar clamps and I find these to be the best.All my panel pieces are cut,jointed,and then rev. glue jointed on the shaper.I also use Titebond.In thirty fiveyears,I've never had a problem with a panel failure,or any kind of Glue failure.I admit that I did't read the article,but he is definitly wrong about the hand-squeeze type clamps.

Oscar

[Bill Wyko]

Slightly OT, but what struck me was the fact that a Quick-Grip clamp was rated at 470lb, whereas a parallel jaw clamp was rated at 370lb.
I said the exact same thing to my BIL last night. I feel that there needs to be some glue left in the joint to, well, glue it together. As far as those clamping preasures go, that can't be correct.

[Doug Shepard]

Well the article did cause me to tighten my clamps a bit more than usual and add a few more this morning. This was for an epoxy glue-up that he didnt use, but I'll keep my fingers crossed. So far I've still got a fairly normal bead of squeezeout between all the joints so I dont think I'm starving the joints.

[Bill Wyko]

When I do segmented turnings, I just rub the 2 pieces together to get a good coverage and the only squeeze out is from pressure I apply myself. My glue joints come out very tight and have never failed to date. I truly think there needs to be a thin film of glue in the joint for maximum adhesion. I would guess around 250 to 300lbs of pressure would be adequate. Oh well, what ever works for whom ever I guess.:D

[Cliff Rohrabacher]

It's been my experience that Titebond tends to be pretty squeeze out resistant and I have on several occasions gotten somewhat carried away with my clamping.

However, epoxy can be subject to glue starvation rather readily. I did a maple panel last winter (over clamped it) and in the morning it came apart in my hands.

[John Seiffer]

Keep in mind that magazines have to fill their covers with articles every month. Eventually there isn't much more to be said on a specific topic - after all, the stuff in wood working magazines is rarely news. So they have to keep giving different spins on the same old stuff.

There are lots of ways to do a lot of things - briefly looking at posts in this forum proves that. So I take what I read as potentially interesting - not as potentially the law of the land.

[Steve Schoene]

The manufacturers have been calling for similar clamp pressures for a long time, and it's certainly not in their interests to tell you to do something that weakens the bond. So why haven't all of Norm's, "don't squeeze out all the glue" joints not failed? Because in most cases edge joints have enough strength to perform satisfactorily even if they don't have maximum strength. But since clamping more firmly has such little cost it doesn't pay not to go for stronger.

But the story that also needs telling is how to get a joint suitably prepared for gluing. Again, lots of less than perfectly fitted joints will hold up OK because of the "safety factor" built in, but to get a joint where there is NO visible glue line is a different question. By no line I mean that you can only tell the wood is joined when several grain lines all stop at the same plane under close inspection. That's not what you get directly off the saw, or with a quick pass on the jointer except in the rarest of cases.

[Howard Acheson]

Well the article did cause me to tighten my clamps a bit more than usual and add a few more this morning. This was for an epoxy glue-up that he didnt use, but I'll keep my fingers crossed. So far I've still got a fairly normal bead of squeezeout between all the joints so I dont think I'm starving the joints.

Be careful, that article has not relation to epoxy adhesives. Epoxy requires a certain amount of film thickness to get fully adhesion and strength. Epoxy should not be clamped any more than necessary to keep the parts together. Clamp too tightly and you will starve the joint and it will be weak.

The article deals specifically with PVA adhesions as the author makes clear. While most other waterbased adhesives will be close to the same as far as clamp pressure is concerned, each will be somewhat different.

[Dennis Peacock]

Yea, I read it too and thought it was crazy. This would mean that all the woodworking I've been doing over the past 30+ years is all wrong AS WELL AS meaning that this kitchen table I'm doing would have required over TEN TONS of clamping pressure!!!!! :eek:

I'll just stick with what I know is working for me and let them be all scientific and stuff in the magazine prints. :rolleyes: ;)

[Barry Bruner]

If they would put a little more Fine Wood Working in the magazines and a little less b.s. it would suit me fine. Next week they will have a clamp with a torque wrench on the end of it they are testing. Its more like a consumers report than a wood working magazine. Barry Bruner

[Dixon Peer]

If they would put a little more Fine Wood Working in the magazines and a little less b.s. it would suit me fine. Next week they will have a clamp with a torque wrench on the end of it they are testing. Its more like a consumers report than a wood working magazine. Barry Bruner

I agree. The change in the magazine over the past few years has been sort of like going for the lowest common denominator. I remember when it dealt with rather high end furniture making and such as that. It does now seem to be more about tool testing and projects for the less talented woodworkers among us. That's fine I guess, but they're starting to bore me, frankly. Taunton Press has to do what they have to do to keep the most readers so they can sell advertising, I know, but...

[Jeff Booth]

As an engineer I was interested in the article and actually disappointed that it was so brief. What I would have liked to have seen would have been a graph of resulting joint strength versus clamping pressure. I will bet the curve has 3 distinct regions (too little, approximately right and too much) I would guess there is an ascending ramp of strength versus pressure on the too little pressure region , then a flatish portion where the wood is breaking next to the glue (over a range of clamping pressure) and then finally a descending ramp when you get into the starved joint region from too much pressure.

My guess is that the reason so many people are shocked and express either concern about previous glued panels or feel like knocking the article is that all the gluing methods they have been using are working and they know it. I would not be surprised if there is a pretty broad pressure region where joints achieve at least 80% of maximum strength (from the author's quoted pressure values). Recall from FWW #192 that the loose bridle joints (no wood contact with a 1/64" gap) for PVA were at least 80% as strong as the tight fitting joints.


Everybody complains about FWW. There is always something I like in each issue and usually a lot I can do without, but of all the magazines I have ever read, they are the only ones I keep and reread. I myself most like the articles about furniture and about wood itself. Garrett Hack wrote an article recently about 5 underused North American woods, that was a really cool article.

[Paul Hendrickson]

The PSI at the joint shouldn't reflect the amount of surface area of the clamps - if they're clamping with 500 pounds of pressure, that's 500 pounds. I sure would worry about the wood fibers on a cherry panel using one of those iron bar clamps with 1500 psi of pressure. I'm assuming that you're saying that you can get a lot more clamping pressure at the same psi at the jaws of the clamp if you use the bessey style clamps.


Surface area definetely IS part of pressure. In college physics we calculated the pressure of an elephant's foot compared to an average woman's high heel. Guess which pressure was higher!

[Tom Veatch]

Haven't read the article, but hearsay from another source indicated a need for about 1200 PSI clamping pressure for flatsawn sugar maple. If that's correct, and is any indication of the general need, I guess you can forget about vacuum bagging veneer work since the most a vacuum bag can give you is only about 1/100 of what's needed.

Let's see now. At 1200 PSI, a 1 square foot veneered panel would require a 86.4 ton press.

Obviously something's not right with this picture.

[Dan Forman]

I would hazard a guess that veneer to substrate joint doesn't require nearly the strength that an edge joint in a panel needs. As someone else pointed out, the author was making the claim that in order to get MAXIMUM adhesion (even though it may not be necessary), those clamping pressures were recommended. He didn't say that anything less would lead to immediatle self distruction of the piece.

I wonder if clamping pressure is at all correlated with glue creep?

Dan

[Kent Fitzgerald]

Surface area definetely IS part of pressure. In college physics we calculated the pressure of an elephant's foot compared to an average woman's high heel. Guess which pressure was higher!
David's point is correct. He didn't say that area wasn't important, he said that the area of the glue joint (not the clamp face) is what matters for determining gluing pressure.

[David Weaver]

Surface area definetely IS part of pressure. In college physics we calculated the pressure of an elephant's foot compared to an average woman's high heel. Guess which pressure was higher!

If you give me the surface area and weight or mass of both, I'll give you an answer, but based on the context, I'm going to guess the woman.

Speaking of, we got one of those new bamboo floors in our office at work - one of the new smart looking laminated things, and guess what it can't handle? High heels - it can't handle hard high heels - they dent it. That's sort of along the same lines as what we're talking about.

[Howard Acheson]

>> I guess you can forget about vacuum bagging veneer work since the most a vacuum bag can give you is only about 1/100 of what's needed.

Well, as you said, you have not read the article and are relying of second hand info. The article dealt with a rather narrow type of joint. Namely, edge to edge or other joints where maximum strength was a criteria. There is not much strength needed for veneering. Any adhesive that keeps the veneer from falling off is sufficient. But, vacuum bagging would not be the choice for structural joints.

As to creep, clamping pressure does have some effect. The more closely you can bring to wood surfaces together, the less adhesive there is to stretch.

[Eddie Darby]

If it ain't broke, then don't fix it.

[Gary Keedwell]

Well, from what I have gathered by my experience and what I have been reading, not many people are glueing up so that they get 100 % maximum strength. Now, my question is what percentage is good enough? 80%...70% or even 50% ?

Maybe 50% is all we really need. Maybe the fact that were getting 70-90% is really good enough and we do not have anything to worry about.;)
Thats my 2 cents and I'm sticking by it.
Gary

[Vijay Kumar]

The manufacturers have been calling for similar clamp pressures for a long time, and it's certainly not in their interests to tell you to do something that weakens the bond. So why haven't all of Norm's, "don't squeeze out all the glue" joints not failed? Because in most cases edge joints have enough strength to perform satisfactorily even if they don't have maximum strength. But since clamping more firmly has such little cost it doesn't pay not to go for stronger.

But the story that also needs telling is how to get a joint suitably prepared for gluing. Again, lots of less than perfectly fitted joints will hold up OK because of the "safety factor" built in, but to get a joint where there is NO visible glue line is a different question. By no line I mean that you can only tell the wood is joined when several grain lines all stop at the same plane under close inspection. That's not what you get directly off the saw, or with a quick pass on the jointer except in the rarest of cases.

Norm often reinforces his glue joints with nails. He also does a lot of plywood joints. Does it not make sense that the glue manufacturers, Bruce Hoadley, Dept of Forestry Wood Handbook all have the same recommendations of pressure. Or is it all one giant conspiracy?

Vijay

[Vijay Kumar]

Haven't read the article, but hearsay from another source indicated a need for about 1200 PSI clamping pressure for flatsawn sugar maple. If that's correct, and is any indication of the general need, I guess you can forget about vacuum bagging veneer work since the most a vacuum bag can give you is only about 1/100 of what's needed.

Let's see now. At 1200 PSI, a 1 square foot veneered panel would require a 86.4 ton press.

Obviously something's not right with this picture.

The article only talked about edge gluing boards, not veneering. The article is worth reading.

Vijay

[Greg Funk]

The manufacturers have been calling for similar clamp pressures for a long time, and it's certainly not in their interests to tell you to do something that weakens the bond.
Titebond recommends 'enough pressure to bring the joints tightly together generally 175-250psi for hardwoods' vs the 600-1200psi recommended by the author.

I was very disappointed with the article. The author Roman Rabiej has a good CV and appears to have done research in this area. It was unfortunate he didn't feel the need to share any of it beyond some unrealistic recommendations.

It would be impossible for any hobbyists and 90% of professional woodworkers to glue up a 2" thick maple workbench using his recommendations.

Greg

[Steve Schoene]

Yes, it makes a lot of sense. That's how I was taught, and it's a very good practice. Yeah, you can get boards to stay together without being so precise, but I'll reiterate that you can't make the glue line disappear so thoroughly.

[Chris Padilla]

Pressure is "force per unit area" or Newton per square meter or Pound per square inch (psi).

So 1 lb over 1 square inch is 1 psi. 1 lb over 0.1 square inch is 10 psi. 1 lb over 10 square inch is 0.1 psi.

Cheers :)

[Anchor Sarslow]

I wil ltry ot say this right, hopefully you all get my meaning anyway.

Concerning the Gov't lab tests.

When they do a test it is only to confirm what the manufacturer tells them.. Sort of just a confirmation. SO it will always be likely that the test lab will agree with the manufacturer concerning things like. well clamp presres for glue ups.

If they find something below the range it gets reported and before it gets recorded, the manufacturer wil gwet an oportunity to correct the situation. If they find it is higher/better, in this case, that does not get reported.

[Paul Hendrickson]

David's point is correct. He didn't say that area wasn't important, he said that the area of the glue joint (not the clamp face) is what matters for determining gluing pressure.

I was referencing the difference in a Bessey vs. Quick Clamp from the article, which is what he was mentioning as well. There is no way a Quick Clamp is stronger than a Bessey, until you factor in the much smaller area of the Quick Clamp. Translation: Quick Clamp may have higher psi, but factor in larger surface area of Bessey, and it becomes much more useful.

[Paul Hendrickson]

If you give me the surface area and weight or mass of both, I'll give you an answer, but based on the context, I'm going to guess the woman.

Speaking of, we got one of those new bamboo floors in our office at work - one of the new smart looking laminated things, and guess what it can't handle? High heels - it can't handle hard high heels - they dent it. That's sort of along the same lines as what we're talking about.

It was definitely the woman's heel. And to relate it to this discussion, the woman's heel would dent the bamboo, whereas an elephant's foot would not dent the bamboo but would be more likely to bust up the concrete underneath.

[Howard Acheson]

Concerning the Gov't lab tests.

When they do a test it is only to confirm what the manufacturer tells them.. Sort of just a confirmation. SO it will always be likely that the test lab will agree with the manufacturer concerning things like. well clamp presres for glue ups.



That's not the case here. The Forest Products Laboratory is a function of the USDA who's mission is to develop and publicize the best practises in the wood uses. They publish this info in a document titled "Wood Handbook" which can be downloaded or viewed here: www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

Their tests are not intended to varify the performance of brands of adhesive. Rather they are concerned with how strong a joint needs to be.

[Jules Dominguez]

I read the article and assumed it was correct, given the author's credentials, but could been written more clearly. The required pressures he gave were for what he called "optimum" glue joints, which I had to assume must be much stronger than the wood being glued. If a joint is at all stronger than the wood itself, in my opinion it's strong enough.

So the article would have been more useful if he had expounded on the difference between"optimum" and "adequate" glue joint strength. If I did the arithmetic correctly, it wouldn't be possible, using his numbers, to get enough parallel jaw clamps on a panel to achieve the "optimum" pressure. (I admit I did the arithmetic on a napkin between bites of lunch and don't have the article handy.)

On the subject of the force exerted by the different types of clamps, it was given as force in pounds, not pressure in pounds per square inch. If you divide the pounds of force applied by a clamp by the area in square inches that the clamp is acting on, you get the pressure in pounds per square inch.

[Rod Peterson]

Did anyone else have fear struck in their heart by FWW's article on how to glue up a panel. [snip]

What do the rest of you think?

The author's credentials are impressive; so I feel uncomfortable in questioning his conclusions. But . . .

I'll simply copy what I posted on the wreck (usenet, rec.woodworking) to the question asked there on the subject:

I moved on the instant I saw the glue up with the QuickGrips on it. He
asserts you can get greater pressure with them than K-Bodies? Please.

I bought my first QuickGrips probably 20 years ago. It took me all of
about five minutes to figure out they were possibly okay for some
tasks, but you couldn't depend on them staying clamped and they
definitely couldn't be clamped really hard. Those first ones were also
my last ones.

[Carl Crout]

The article only talked about edge gluing boards, not veneering. The article is worth reading.

Vijay

Wasn't worth reading. As a matter of fact the entire issue was worthless. Why the article on routers for beginners?
FWW wasn't designed for beginners.

Let's just say another goofy engineer who has more degrees than sense wrote that article.

The only thing that I have read is that Franklin (Titebond) recommends that your joints don't have more than a .003 gap. Maybe that goofy engineer can't make straight edges so he has to squeeze the sh#@ out of them to get them to those specs.

[Tim Lynch]

Howie,

Thanks for the link -- lots of information and an interesting read.

[Wilbur Pan]

Norm often reinforces his glue joints with nails. He also does a lot of plywood joints. Does it not make sense that the glue manufacturers, Bruce Hoadley, Dept of Forestry Wood Handbook all have the same recommendations of pressure. Or is it all one giant conspiracy?

Vijay

Despite all the jokes about Norm out there, I don't ever recall him saying that he used nails to reinforce a joint. I do remember hearing Norm say on several occasions that he uses his brad nailer to hold things in place while the glue dries, and that it is the glue that holds the joint together.