Woodworkers… Clamping pressure?

[Paul Simmel]

Up until about 15 years ago, I over tightened everything… but not anymore.

On well machined pieces.

Since then, here’s what I do. On panel glue ups for example, I have used moderate pressure and watched my squeeze out as a gage of how tight to tighten the clamps. With a moderate amount of glue, I’m using finger pressure while turning my wrist and when I get a nice, even squeeze out I stop. With ¾” pipe clamps, say every 12” or so (3” boards), clamps on bottom and top (tops used to bring opposing force to keep the panel level only). When everything is nice and flat after finessing with a straight edge, I let it dry.

I have never had a glue failure with this method. I use the clamps more for equaling pressures and pulling things into level or square than consciously thinking about how tight they “must” be.

On another forum, I was reading how they do it. There, they crank ‘em to max and “engineers” and “physicists” supported that… stating that 1800 psi per clamp was justified in order to comply with the following info:

From the Titebond website:

>>> Required clamping pressure Enough to bring joints tightly together (generally, 100-150 psi for softwoods, 125-175 psi for medium woods and 175-250 psi for hardwoods)

I would really like to hear what experienced woodworks have to say about their clamping techniques.

Edited-out image HTLM.

[Paul Simmel]

You know how it is when your sanity is challenged! (You turn toward a source of sanity)

Thank you folks who are responding.

Please comment if you so feel.

By far there is little said on clamping pressure. If you Google it, there’s nothing, really.

It’s not that I can’t take counter arguments. I welcome them. But I prefer to “argue” with woodworkers and not scientists.

Just vote if you don’t want to comment. I thank you!

[Dennis Peacock]

Paul,

I try to do good machining so I don't have to "force" the wood joints to look good by applying more pressure. One thing I learned a while back, you can squeeze most all the glue right out of a joint.....so I do crank'em to the max no-mo. :rolleyes: :D

[Paul Simmel]

Dennis,

I agree 100%.

On the other forum, the counter-argument against starving a glue joint was… no one complains about it.

In all honesty, I can’t remember the exact project on which I had my first failed glue joint, but I do remember it was back before I learned to not tighten so hard.

That was also back before I had machinery to make nice, bow-free joints.

-=-=-=-

There are a lot of experienced and far-beyond-me woodworking talents posting on this board. I’m not putting myself down, I have talent and experience too, but there are some VERY talented people here.

Thank you, Dennis.

[Don Bullock]

I never recall a failed glue joint, but I used to crank my clamps to the max and then some. One time I cranked a table top to the point that it had a bow in it. Fortunately in those days the glue had a longer set time so I was able to discover the problem in time to get the top flat. Part of the problem I realize now, in addition to clamping it too much, was that I did not have enough clamps. Now, that I'm older, and hopefully wiser, I crank them for "enough for good squeeze out."

[Mike Cutler]

I primarily use epoxies for glueups, so low pressure is all that is required.

[Chris Barton]

The purpose of the clamp is to hold the piece in place with good surface contact until the glue dries. However, there are those folks out there that think that the tighter you clamp the work, the stronger the joint (and this used to include me). I have learned what Dennis has, clamp pressure is not a solution for a poorly machined fit. A well machined glue surface can be held together by tape. And, that's often exactly what I use. In some instances I use no clamps at all, just a "rub" fit.

[Greg Deakins]

to me it seems that if you squeeze tighter, it will force it into endgrain, but that doesn't apply for other glue ups. I broke a wood clamp trying to get max pressure once, since then I have never cranked too hard, but good and solid no less.

[Mark Singer]

I give good pressure....a lot of pressure will not make up for a poor fit. If the wood fits well a moderate amount of pressure and applying glue to both surfaces should be fine...

[Byron Trantham]

It took me a while to realize that "tighter is not better". If I have to really tighten a joint, there is probably something wrong with the joint. Dry fitting really helps in making this determination.

[Howard Acheson]

According to the Titebond webpage and the Wood Products Handbook from the US Forest Services, PVA adhesives (white and yellow) require 200-250 psi of pressure for maximimum strength and minimal glueline when gluing hard woods. Soft woods require about 100 psi.

3/4" pipe clamps produce about 1,000 pounds of force. Parallel face clamps (ie: Bessey, etc) produce about half of that.

So, if you are glueing up a panel of 3/4" thickness that is 12" long the pressure needed is 12" x 3/4" x 200 psi which is 1,800 pounds of force total spread equally along the glueline. As a 3/4" pipe clamp, fully tightened, can exert 1,000 pounds, you will need two clamps fully tightened.

In reality, you can not overtighten most joints. The wood itself will deform before there is any damage to the joint. Also, once the adhesive has wetted the joint you will get a good joint regardless of the pressure as long as the minimum pressure is applied. There is no such thing as "starving the joint" in spite of some TV woodworkers opinion.

Now, it's true that you can get a strong joint with less pressure if the surfaces of the joint are mating perfectly. With PVA adhesives, it's the bringing closely together of the wetted wood cells that provides the strength (there is no strength in the adhesive itself unless epoxy is used).

[glenn bradley]

I learned my lesson on a cutting board I over tightened. Squeezed out too much glue and had joint failure before the project was finished. f the joint fits properly and I've got good squeeze-out, I'm done.

[Cliff Rohrabacher]

Tighten 'em up get clean squeeze out and stop there.

I prefer more clamps over more force to distribute the energy more widely.

Epoxies can be goofy. West Systems glues are somewhat runny so they can experience starvation from squeeze out more readily.

[josh bjork]

Byron, I am learning the fruit of dry fitting and it helps a lot. I think it helps you determine the right glue for the job as well. There are instances where you just can't apply pressure in a direction. If you just choose the right glue, all can be well. I ain't a CNC machine. Tolerances aren't near .002 and it is ok because there are glues for such situations.

I think there is a serious lack of education about glues. Many of the threads get quite heated but all the arguement is usually opinion. There is a big difference between what "will get by" and what is optimal.

[Howard Acheson]

>> West Systems glues are somewhat runny so they can experience starvation from squeeze out more readily.

Epoxy adhesives get their strength from the film of epoxy itself--unlike PVA, Polyurethane, Urea Formaldehyde, etc, which get their strength from a chemical reaction between wood fibers and cells. Therefore, epoxy should only be clamped enough to hold the joint together or very lightly. With epoxy you want a layer of glue between the joints.

[Jules Dominguez]

I clamp for good squeeze-out and a hairline joint. I dry fit first and straighten boards as needed before glueing.
I don't go anywhere near as tight as I could with the clamps. I use Besseys and/or pipe clamps.
How the heck are you supposed to know how many psi you're exerting on the wood? You can't, so referring to clamping pressure in psi is useless in my opinion.

[Gary Keedwell]

Up until about 15 years ago, I over tightened everything… but not anymore.

On well machined pieces.

Since then, here’s what I do. On panel glue ups for example, I have used moderate pressure and watched my squeeze out as a gage of how tight to tighten the clamps. With a moderate amount of glue, I’m using finger pressure while turning my wrist and when I get a nice, even squeeze out I stop. With ¾” pipe clamps, say every 12” or so (3” boards), clamps on bottom and top (tops used to bring opposing force to keep the panel level only). When everything is nice and flat after finessing with a straight edge, I let it dry.

I have never had a glue failure with this method. I use the clamps more for equaling pressures and pulling things into level or square than consciously thinking about how tight they “must” be.

On another forum, I was reading how they do it. There, they crank ‘em to max and “engineers” and “physicists” supported that… stating that 1800 psi per clamp was justified in order to comply with the following info:

From the Titebond website:

>>> Required clamping pressure Enough to bring joints tightly together (generally, 100-150 psi for softwoods, 125-175 psi for medium woods and 175-250 psi for hardwoods)

I would really like to hear what experienced woodworks have to say about their clamping techniques.

Edited-out image HTLM.
You know the old joke about trying to drive someone crazy....Bring them to a round room and tell them to sit in a corner?:D
Well, I say substitute PSI for glueing boards together and you will end up in the same looney bin.
As has been stated above, proper preperation of said boards or joints and a "squeeze-out" with a little snug-up afterwards will do good for one's mental health.
IMNSHO
Gary K.;)

[Rick Christopherson]

What I just don’t understand about these discussions is that the glue manufacturers specify how much pressure is required for a proper joint, but some woodworkers dismiss this simply because they don’t understand it. You may not know how your car’s transmission works or why it needs a specific grade of transmission fluid, but does that mean you would deliberately put in the wrong kind simply because you don’t know why the right kind is the right kind? Of course not. You put in the type that the manufacturer specifies, even when you don’t know what the difference is.

A lot of the same woodworkers that are claiming that they just barely clamp their joints are also the same ones that are buying the tinted glues to conceal the resulting visible glue lines. I just saw Norm Abram use a tinted PVA glue last week, saying that he was using it so the glue line was not visible. Well, the glue lines were visible because he wasn’t following the manufacturer’s instructions for the specific glue-type in the first place.

This isn’t a matter of one person’s opinion over another--it is a matter of what the manufacturer is specifying. So why would anyone deliberately contradict the manufacturers?

Maybe part of this confusion is that woodworkers are confusing the specifications for some types of glues and misapplying them to other types of glues. This is just as detrimental, because not all glues have the same specifications. Some glues will fail if they do not have a thick enough joint, but others will fail if they have too thick of a joint, or not enough pressure.

The point of the discussion is not that you have to crank the crap out of your clamps, but that by just barely snugging them up, you are operating well below the manufacturer’s specifications for PVA glues. Unfortunately, these discussions seem to only address the polar extremes because people misinterpret the concepts. The idea of cranking the heck out of your clamps wasn’t originally presented as a requirement for clamping, but as an explanation that it is impossible to starve a joint--which was an extremely prevalent topic years ago.

You don't need to know the exact clamping force of your clamps, but you do need to know that "finger tight" is below specifications.

[Paul Simmel]

I have successfully glued pieces together with packing-tape wrapped around (the kind that stretches when pulled), and the few spring clamps I have are way too strong for just about any application.

Also, as the glue dries, it is my sense that the glue “sucks” the pieces together like wallpaper paste sucks the paper to the wall.

[Gary Keedwell]

Another thing which I don't think has been mentioned is that one's interpretatation of "squeeze-out" is not the same for everybody.
If one slops the glue on thick...obviously it won't take much to have a "squeeze-out" .
If one spreads a proper thin layer of glue on both surfaces...then a proper
"generalization" is that the glue has enough pressure to be squeezed out. We are not talking "rocket science" here. Obviously a little common sense is in order.
Speaking of "generalizations", I'm assuming ( yes I know what assuming means:rolleyes: ) that we are talking about good old yellow glue here, which "most" of us use on a daily basis.
By the way, I will humbly say that I have projects that are 27 years old that haven't failed yet and I bet there are alot of you woodworkers that have some that are alot older then mine.
I only say that to relieve some of the insecurities of some of the younger woodworkers who may worry. After all...this IS just a hobby for alot of us....;)
Gary K.

[Eddie Darby]

I found that this site was helpful when it came to clamping:

http://www.bowclamp.com/

[Andrew Williams]

Depends on the application. Face gluing wide boards into thick slabs requires more pressure than edge gluing boards into a tabletop. Some applications I dont clamp at all, like dovetailed joints, I just ease them together with hammer and block. M&T joints, for the most part, only enough pressure to close the gaps in the tenon shoulder. For expanding dowel joints I clamp them until they are flush, then take the clamps off immediately.

[Paul Simmel]

>>> This isn’t a matter of one person’s opinion over another--it is a matter of what the manufacturer is specifying. So why would anyone deliberately contradict the manufacturers?

Firstly, what the manufacturer specifies is a certain psi for their glue, and as specified for Titebond, between 100 and 250 psi depending upon softwood and hardwood.

Yet we have a strong majority (myself included with years of experiential success) who do not crank their clamps to anywhere close to their clamps’ maximum.

What does this tell us?

It says two things. One, watching glue line squeeze out tells us we have a situation where we can tell when enough pressure will “bring joints tightly together”, as recommended by the manufacturer. Two, by having no glue failures some twenty or more years later, something we are doing is correct.

The “simple” physics and or science involved as to how tight one must crank, based on square-inches times psi is flawed in practical use as it has been argued by me elsewhere.

-=-=-=-

Put another way. If my calculations tell me that when I drop a ball it will hit the floor, but upon practical experience the ball flies to the ceiling when I let go, time and time again, I will seriously re-check my calculations. The original calculation may have been flawless in my Ivory Tower, but so many balls on the ceiling can’t be denied after all.

[Joe Chritz]

9 out of 10 voices in my head say I'm not having sanity issues.

If you have to force a joint closed it won't last well anyway, so I tighten about... yaah much with just a skotche more.

I try to use the K-bodies for panels for the flatness aspect and they don't seem to generate the pressure the pipe clamps do.

Joe

[Clayton Masterson]

Maybe the clamping pressure specifications outlined by the manufacture is just a bit of CYA? While reading this some guys say that they clamp the hell out of joints and others merely snug them up.
As far as my own experience, in doing some remodeling jobs, the miters on the door casing will remain intact while the wood itself breaks. No doubt that this proof positive that a "properly fit " joint does not need near 250 lbs of clamping force. How would you do that on-site, realistically?
Anyway, just a thought.

[Brian Hale]

How do you know when you've reached 250 psi?

If 5' 2" 125 lb woodworker cranks the heck out of a clamp, is it the same as when a 6'10" 350 lb woodworker (who is a bricklayer full time) when he cranks the heck out of a clamp?

I think not.

When clamp manufacturers add a PSI scale to their clamps we'll have something definitive to discuss. ;) Untill then, i'll snug them up pretty good and then add a touch more,,,,,,,,,,,,,,,,,,,,,

Brian :)

[Rob Blaustein]

...It says two things. One, watching glue line squeeze out tells us we have a situation where we can tell when enough pressure will “bring joints tightly together”, as recommended by the manufacturer. Two, by having no glue failures some twenty or more years later, something we are doing is correct.

The “simple” physics and or science involved as to how tight one must crank, based on square-inches times psi is flawed in practical use as it has been argued by me elsewhere.


But isn't looking for squeeze out--as a general rule--just as impractical as trying to target a particular pressure? As Gary pointed out, squeeze out is very subjective in that it depends on the amount of glue you add. If you add a lot you may get squeeze out well before you hit an appropriate clamping pressure. So for the beginner who hasn't much experience with how much glue to add, and adds too much, this could be misleading. But for the more experienced ww'er who applies an amount where squeeze out will occur at a good clamping pressure that rule might work fine (as it seem to have for several here).

[Art Mann]

Yet we have a strong majority (myself included with years of experiential success) who do not crank their clamps to anywhere close to their clamps’ maximum.

What does this tell us?

It says two things. One, watching glue line squeeze out tells us we have a situation where we can tell when enough pressure will “bring joints tightly together”, as recommended by the manufacturer. Two, by having no glue failures some twenty or more years later, something we are doing is correct.


What your observation tells me is that PVA glue is strong enough that the average user can get away with less than optimum clamping pressure and still get satisfactory results. That is all it proves. Glue squeeze out is only a function of how much glue you applied inthe first place. It does not say anything about clamping pressure.



The “simple” physics and or science involved as to how tight one must crank, based on square-inches times psi is flawed in practical use as it has been argued by me elsewhere.


Someone who had no knowledge of physics made a faulty arguement because it seemed intuitive and some people accepted that as factual. As a design engineer, I have spent a career learning the hard way that what intuitively seems right usually isn't if it violates commonly accepted design guidelines and/or manufacturer's recommendations. I have witnessed such assumptions costing a certain automobile manufacturer hundreds of millions of dollars in recall expenses.



Put another way. If my calculations tell me that when I drop a ball it will hit the floor, but upon practical experience the ball flies to the ceiling when I let go, time and time again, I will seriously re-check my calculations. The original calculation may have been flawless in my Ivory Tower, but so many balls on the ceiling can’t be denied after all


Your arguement (and this silly poll) sounds a little like the scientists who claimed the earth was flat because if it weren't, everything would fall off. If we can believe history, that was the majority opinion in Galileo's time.

You haven't offered any useful evidence that moderate clamping pressure will produce as strong a joint as that produced according to the glue manufacturer's specifications. You will not convince me until you have constructed identical joints on many test pieces with known clamping pressures and then destructively tested these joints with suitable equipment. I am pretty certain that that is what the glue manufacturers did when they came up with their recommendations in the frist place.

Several months ago, I constructed some test miter joints on 3/4" by 1" cherry strips. These joints were not reinforced in any way. I only used corner clamps and the clamping pressure was - I would guess - 25 psi. I was attempting to prove to myself that a certain construction technique would hold in the particular application (jewelry box) without additional reinforcement. No decent craftsman would use this technique under normal circumstances. What I found was that these joints were amazingly strong and exceeded my expectations. What did that prove with regard to maximum strength? Nothing! It only proved that PVA glues are stronger than I thought under much worse than ideal conditions.

[Tim Sproul]

According to the Titebond webpage and the Wood Products Handbook from the US Forest Services, PVA adhesives (white and yellow) require 200-250 psi of pressure for maximimum strength and minimal glueline when gluing hard woods. Soft woods require about 100 psi.

Here is an exception to 'chew' over. Titebond makes a cold press glue that is (IIRC) a PVA based adhesive and the recommended pressure is also ~200 psi.

There are quite a few of us who have successfully used Titebond's cold press glue in vacuum presses (max out at 14 psi) without problems of veneer delamination. Trying to acheive the kind of pressure they recommend pretty much requires a press similar to what plywood manufacturer's use. Typically, such contraptions aren't available for your everyday woodworker. A small 12 inch x 24 inch panel would require 57,600 pounds. I'd like to see someone build a wood press that can exert that kind of force.

I suspect that a well made joint allows for a lot less pressure than 100 - 200 psi. In the end, we should all do what works for ourselves.

[Gary Keedwell]

"Your arguement (and this silly poll) sounds a little like the scientists who claimed the earth was flat because if it weren't, everything would fall off. If we can believe history, that was the majority opinion in Galileo's time."

First, I would like to thank the original poster for the interesting poll. Far from being "silly" I thought it interesting to see other woodworker's glueing-up ideas.

Second, the analogy of the ball hitting the ceiling with the earth being flat is a little flawed. You can see the ball hitting the ceiling but has anybody seen a ship fall over the edge? Come on!!!:o
Anyways, I can tell you , as a matter of FACT, that manufacturers will not put anything on a label untill an army of lawyers read it a thousand times to see if it will come back and bite them in the form of litigation.
Go around your place of habitation and pick up a few products and read the labels. They are always protecting themselves from being sued.
I once asked an engineer why the tolerances were so tight on all the parts that we machined ( we made our own product). And he replied that if he made the tolerances twice as tight as he needed....and we only made it half as good in the shop.....the parts will still work.:cool:
Anyways, maybe glue in the "earth is flat days" needed that extra pressure to work properly, but in this modern "round earth days" the technology lets us tighten our clamps with the force of humans not gorilla's.;)
Gary K.

[Andrew Williams]

I thought that the secret to PVA glue was not in the pressure, but in getting the pieces of wood close enough together so that the actual line of glue is pretty thin, but a complete coverage, since some of the glue enters the grain of the wood as well. Squeeze-out indicates this and as long as the pieces are properly jointed, it should indicate the time at which the clamping force should stop. If badly jointed, more clamp force would be needed to achieve the proper distance between pieces over their full length. If too much squeeze-out is achieved, then what you have left will not have enough glue to bridge the gap between the wood pieces, once the grain pulls the glue in.

In my experience, hot hide glue is quite different, it appears to resist the pressure from clamps considerably, and I have not seen much difference between a clamped joint and a rubbed joint. As the joint dries, it pulls the two pieces together with some kind of hydraulic action that I have yet to fully understand. They start out looking like joints with large glue-lines, and eventually have a very fine line, once fully cured.

[Howard Acheson]

>> There are quite a few of us who have successfully used Titebond's cold press glue in vacuum presses (max out at 14 psi) without problems of veneer delamination.

Tim, that has no relevence whatsoever. That is certainly not an application that requires high strength.

[mark page]

I side with Brian on this matter. I have items made from my father and grandfather that span almost a century of woodworking. Technologies have developed and changed a lot in that time span. General procedures I believe have not. I have to admit that I do not make my living as a professional woodworker, but my previous relatives definately were craftsman and made a good living at it. I have not personally had a glue joint failure, nor has the pieces that I own that my two generations before me have created. I do it as I was taught, what little I have learned from them, was a snug fit and a smidgen more, not a tad but a smidgen, tad was too much....
Now we open a whole new thread of how to measure tads and smidgens.

Now if someone wants to take a 20lb post mall and try to destroy something I make or my forefathers made, then I guarantee that it will be destroyed. It was not meant to take this abuse. But a century of quality made items through generations of childrens abuse prove that they knew what they were doing. I am continuing in just what I was taught. And a subnote: My children could tear up an anvil in a sandpile:eek:

[Paul Simmel]

>>> You haven't offered any useful evidence that moderate clamping pressure will produce as strong a joint as that produced according to the glue manufacturer's specifications.

And you have not included the structural member’s strength in any calculation!

If I am gluing up ¼” strips (if I don’t have a caul) I will use a clamp every inch. If I am gluing up 8” boards, I will use a clamp every 18” or so (maybe 24” depending on the material’s strength)… with moderate pressure.

Why do I do this? Because I know I will not have a glue failure.

How much glue to put on? Enough so that there is some squeeze out, not much more. WHY? Because squeeze out tells me all of the joint has been saturated with glue hence a film between the two. What else does squeeze out tell me? It tells me I have a tightly fitted joint. PSI tells me absolutely nothing and I could care less about it.

Somehow, for me to state that with moderate pressure one can achieve both straight and strong joints, it is an insult to you at least to the point that you feel the need to call the poll “silly” and to judge those participating with the mentality of “flatlanders”.

It’s not that we are stupid, we just don’t have failed glue ups, and we know this from experience. Some of us (I included) can tell you of starving a joint. That is to say the dang joint failed due to the fact that most of the glue was squeezed out of the joint due to the fact that the joint was excessively clamped.

The thread may be “silly” to you, but for me it is vindication, because I was told that I was flat-out wrong and not smart enough to speak on the same level as an engineer or a scientist who had paper credentials hanging on walls…. that I had been proved wrong so I should just “let it go”.

No one has addressed my question as to what value is to be given a structural member to be glued, which is something experienced woodworks inherently learn in their “feel”.

1800 pounds of pressure was recommended for clamps spaced 12” apart for 3” boards. My innate inner voice tells me this is extremely excessive.

25 – 100 years of glue-up success is to be sure anecdotal, but in the case of a woodworker, it is very strong evidence as well.

Finally, if the glue joint in its “weakest” form, is stronger than the structural members themselves, then the “strongest” joint argument is moot from day one.

I sincerely hope the thread continues. This is valuable info here.

[Paul Simmel]

The other forum I referred to, just deleted a similar poll-thread on the same subject in which the majority started to rise to support lighter clamping pressures as well. There was a link there to this thread here. (I didn’t start that thread)

Cheers to SMC.

A little contention is always welcome in my view. I don’t know what happened over there to get the thread closed (can’t even access it), but here it is civil (thank goodness).

[J.R. Rutter]

So, if you are glueing up a panel of 3/4" thickness that is 12" long the pressure needed is 12" x 3/4" x 200 psi which is 1,800 pounds of force total spread equally along the glueline. As a 3/4" pipe clamp, fully tightened, can exert 1,000 pounds, you will need two clamps fully tightened.


Sounds good to me. My Plano clamps max out at just over 1700 lbs of clamping pressure, and I typically space them about a foot apart. I tend to tighten close to max. What's a glue line? ;-)

[Mike K Wenzloff]

The other forum I referred to, just deleted a similar poll-thread on the same subject in which the majority started to rise to support lighter clamping pressures as well. There was a link there to this thread here. (I didn’t start that thread)
...
A little contention is always welcome in my view. I don’t know what happened over there to get the thread closed (can’t even access it), but here it is civil (thank goodness).
The thread over there was killed following a couple of my posts. The responses to those two posts were, uh, not very kind.

As for the civility, some of the posters here in this thread were less than kind over there in their posts.

Take care, Mike

[Gary Keedwell]

The thread over there was killed following a couple of my posts. The responses to those two posts were, uh, not very kind.

As for the civility, some of the posters here in this thread were less than kind over there in their posts.

Take care, Mike
Could you give us a hint on what Forum you guys are talking about?:rolleyes:
Gary K;)

[Lee Schierer]

I use 98% PVA glue in my cabinets.

I voted for "Other", while I don't tigten my clamps to their breaking point or just under, I do apply pretty good pressure and I tend to use a lot of clamps. I own mostly 3/4" pipe clamps. When gluing up panels I normally space my clamps on alternate sides of the piece every 6" or so. After checking the pieces for dry fit and grain arrangement, I apply an even film of glue on the entire surface about 1/64 inch thick on one piece. Pieces that show any gap get jointed so you can't see any light between them when held with hand pressure.

When I clamp I see small beads of glue about the size of a pin head about every 1/8" or so along the glue line on both sides of the board. Glue drops that drip or run indicate you used too much glue. Absence of glue droplets if your clamps are tight indicates you either waited too long to get the clamps on or you didn't put on enough glue and you are apt to get a joint failure. Clamps are generally tight enough to deform the edge of the wood about 1/32 to 1/16" so I use glue blocks on every clamp face to spread out the force being applied.

Inadequate clamp pressure leaves too much glue in the joint and will also weaken the joint. Since I started properly making my joints, I've never had a glue joint fail, but I have had hickory panels crack when I didn't allow for movement. In both cases where this occurred the wood split, the glue joints were still intact.

[Mike K Wenzloff]

Hi Gary, it really doesn't matter as the thread was killed. I do have a copy of the entire thread up through my responses--I was a late comer to the party there because, well, I rarely leave the comfort of the hand tool forums.

I guess I had a moment of insanity and put my two-cents into a thread which was generating a lot of heat already in a section of the forum I don't post a lot to. Kinda like here, too. Mainly hand tool stuff.

Take care, Mike

[Art Mann]

Somehow, for me to state that with moderate pressure one can achieve both straight and strong joints, it is an insult to you at least to the point that you feel the need to call the poll “silly” and to judge those participating with the mentality of “flatlanders”.

Let me tell you why I think the poll is silly.

1. First of all, you did not give enough information in your poll, nor offer enough suitable answers, for someone to provide a correct reply. Elsewhere in you response you made that point yourself. Clamping pressure depends on the number of clamps used and the stiffness of the thing being clamped. The specifications supplied by Titebond are in terms of pounds per square inch of glued surface area. There is no way to calculate or estimate this essential information from your poll.

2. It seems ridiculous to me to try to determine optimum clamping technique by using a poll. The manufacturer has doubtless done many studies using destructive testing to answer this question. I will not attempt to answer questions about chemistry or strength of materials based on a poll. I will remind you once again that a poll of prominent scientists in the days of Galileo would have claimed the world was flat. They would have provided overwhelming believable anecdotal evidence to prove their point.

3. It seems to me that a poll on Woodnet did not confirm your opinions and so you sought confirmation elsewhere. Would you have gone to the Family Woodworking board, or some other, if the opinions here had not been favorable? Are you looking for information or affirmation?

There is no doubt in my mind that PVA glues will do an adequate job with clamping pressures that are far less than those required to achieve maximum strength. I offered an example of that in a previous post. Does that mean that we should just accept nominal strength of a wood joint when maximum strength could be achieved with an additional clamp or two or maybe another quarter turn on the crank handle?

There is an opinion floated by the god of hobby woodworking, Norm Abrams, that you can starve a PVA glue joint by overtightening clamps. The manufacturers of the materials state otherwise. I have learned over 25 years as a design engineer that the sure bet is with the material manufacturer.

[John Stevens]

Several months ago, I constructed some test miter joints on 3/4" by 1" cherry strips. These joints were not reinforced in any way. I only used corner clamps and the clamping pressure was - I would guess - 25 psi. [snip]What I found was that these joints were amazingly strong and exceeded my expectations. [snip] It only proved that PVA glues are stronger than I thought under much worse than ideal conditions.

Interesting anecdote and good point. Here are a couple other examples. While making a prototype of a narrow (~8") cabinet, I included a fixed shelf made of chipboard, that was butted and glued against the inside walls, with no mechanical joinery at all--nothing but glue. The fit was as close to perfect as I could get it, and I used a lot of clamping pressure with yellow PVA glue. After the glue cured, I was able to stand on the shelf without even a creak. The other example is when you assemble a mitered box by laying the four sides next to each other so the insides are facing down, taping the outsides of the joints, flipping the whole thing over so the insides are facing up, applying glue to the edges, folding the sides together and taping the last side shut until the glue cures. No clamps used, but the resulting box is amazingly strong.

My conclusion was the same as yours--modern PVA glues are incredibly strong. And perhaps we share the same philosophy about disregarding the manufacturer's recommendations: "proceed at your own risk."

[Gary Keedwell]

:o I'll say it again. Litigation....litigation...litigation.....They always cover their backside. If you do have a glue failure or such that somehow caused personal injury.....it will be there on the label that you didn't apply enough pressure...CASE CLOSED.:eek:

Gary K.

[Art Mann]

:o I'll say it again. Litigation....litigation...litigation.....They always cover their backside. If you do have a glue failure or such that somehow caused personal injury.....it will be there on the label that you didn't apply enough pressure...CASE CLOSED.:eek:

Gary K.

That sounds a pretty "far fetched" to me. About the only way they could be held liable in such circumstances is if the product were proven to be defective or it could be proven they published bad usage recommendations and then somebody got hurt because they followed them. The truth is it would be just as easy to clam excessive pressure as not enough. Why is it so hard to believe that a company would do research on their own product and then make recommendations on it's use based on that? It seems people are going to great lengths to avoid acknowledging the obvious.

[Gary Keedwell]

Well, maybe I'm a little cynical, but LOML is a stenogragher who works with lawyers every day...and I worked for a manufacturer who wouldn't belch before consulting with their lawyers.
In this litigious conscience society, big companies need to be very defense minded. Anything you put in print, especially labels on one's own product, has to be scrutinized with a fine tooth comb by an army of lawyers.
If you think about it, almost every thing we glue up has to be safe. You lean, stand,sit, lift, push, pull etc, etc. on every thing we make. Right?
I'm sure there is alot of useful information on labels for our benefit.....but still I see lawyers in my mind looking at every word that is written on them.:o
Gary K.

[Paul Simmel]

>>> 3. It seems to me that a poll on Woodnet did not confirm your opinions and so you sought confirmation elsewhere. Would you have gone to the Family Woodworking board, or some other, if the opinions here had not been favorable? Are you looking for information or affirmation?

Sir, this poll here was started before the poll on woodnet, and I can't even recall if I voted on the woodnet poll.


Ok. I’m going to bite, and get this off my chest completely.

SMC was the first forum I subscribed to. SMC has by far more members and traffic than any other forum I know of, and the talent here is superlative and the people here are 99% nice.

In my limited experience with Woodnet, though also a wealth of information, I have found it to be a completely different “feel” in terms of some of its members.

My arguments were ignored over there on a thread called, "How to use a clamp", and I was told that because I didn’t have a sheep skin on the wall I should just basically shut up. I found it snotty, and it seemed to me that there was a sense of enjoyment from some who took pleasure in putting others down. Here’s another one from you, here on this thread:

>>> 2. It seems ridiculous to me to try to determine optimum clamping technique by using a poll. The manufacturer has doubtless done many studies using destructive testing to answer this question. I will not attempt to answer questions about chemistry or strength of materials based on a poll. I will remind you once again that a poll of prominent scientists in the days of Galileo would have claimed the world was flat. They would have provided overwhelming believable anecdotal evidence to prove their point.

In no way did I ever allude to this being a scientific poll. I said in the original post, and elsewhere why I wanted to know what others did.

>>> I will not attempt to answer questions about chemistry or strength of materials based on a poll.

That’s just another evasion of the question none of you has been able to answer, and frankly what would probably end this argument.

I’ll ask again. What value do you place on the structural strength of the members you are clamping, and where in your calculations is that value entered?

Until you can answer that, I don’t think your references to any manufacturers requirements loft your position.

Furthermore, the Titebond website simply states: “Required clamping pressure Enough to bring joints tightly together (generally, 100-150 psi for softwoods, 125-175 psi for medium woods and 175-250 psi for hardwoods)

It does not tell you how many clamps or how tight, on what boards, how thick and how wide. IMO, it <can’t> tell you that because how is Titebond going to determine the structural strength of each virtually limitless combinations of glue-ups? Also, the Titebond website does not, that I can find, have any reference to a stronger, or more optimal joint opposed to a lesser joint.

1800 pounds of pressure per clamp was arrived at by calculating the thickness of the board, (3/4”) with each clamp spanning 12”, by dividing or multiplying (I forget) the pressures of the respective clamps across the 12-inches of ¾” surface. So what I want to know is where in that calculation does it account for the board’s structural strength?

My very non-scientific inner sense tells me that when I am clamping my boards together, the clamping pressures are being transferred along the structural members themselves… that between the 2 clamps the pressures are less in the very middle of my span, but incrementally so. Right next to the clamp, maybe an inch or two, the pressures are going to be greater, etc. Actually, the pressure will be at its greatest right behind the threaded rod on the ball joint. The pressure is transferred from there to the clamp’s metal pad, and through the board incrementally across the span.

I’m sure this can be calculated by someone… short of mini pressure gages placed every inch. ITMT, even though I suspect a certain psi is present, aside from experience and anecdotal accounts, I can’t prove what that pressure is. I don’t know what value to place on the member’s themselves… but I strongly feel that they must be considered in any equation… in the exact same way a cantilever is calculated. I know from experience, that a few feet out with 2 x 12’s 16” o/c is going to support my deck, my second floor, etc., by transferring the load through its structural members to approved uprights right down to the footings.

Moreover, anecdotal evidence in woodworking is very much different than anecdotal evidence supporting the belief in a world being flat. The anecdotal evidence we are talking about here is based on practical demonstration and experience accumulated based on this feedback. There is a certain “scientific” conclusion that can be made if our furniture doesn’t fall apart and remain in one piece for decades. So in that sense, this poll for that reason only, is valuable and somewhat more conclusive than what one may tell about why the world is flat. No one ever did fall off the edge, but if after a few test-runs one did, then it would be much more conclusive. I realize that your reference to the mentality which must exist for one to believe in a flat world was really more of a comment directed for other reasons.

I think it was very hasty to conclude what clamping pressures need to be without considering the member’s strength and how those strengths contribute to the manufacturers recommended psi.

I will not be speaking with you again, sir.

[Bob Hallowell]

I took a hand tool seminar once where the instructor hand planed both edges on 2 foot boards and rubbed on yellow glue put the 2 boards together and slid them together and set them aside. Afew hours later he challenged us to break them apart which we couldn't. He said the vacuum created by the perfectly smooth surfaces was all it needed to hold it together for the glue to set. He said he uses his power jointer but always takes a swipe or 2 with the plane to smooth out the ridges left by the jointer. if you use a power jointer alone you have to use alot more clamping pressure to overcome all the little hills and valleys left.

Bob

[Rick Christopherson]

Paul,
Did you not notice that I was a member of this forum and that you were referring to me in your postings in a derogatory manner? (I'm not offended, but I don't believe you knew I was here.)

The reason why you got the responses in the other forum that you did, was because of the ridiculing nature that you made with your postings. I answered the questions that you just posed (both here and there), but because you couldn’t come up with a legitimate defense to your original postings, you started this new poll at SMC. You directed your posting here directly at me, but you didn’t use my name, per se.

Now that we are on the fourth page (by my settings) of this thread, and you have once again said the same things here that you were not able to defend on the other forum. Do you think that saying this somewhere else is going to make it more true than it was elsewhere?

Even though I previously participated in this thread, you obviously didn’t notice that I post here. So before I respond to the questions in your latest posting, would you like to edit your posting to change the questions for which you already know that I am capable of answering?

Such as:
I’ll ask again. What value do you place on the structural strength of the members you are clamping, and where in your calculations is that value entered?

Until you can answer that, I don’t think your references to any manufacturers requirements loft your position.I have answers to all of the questions you posed in the above posting. As I told you before, just because you don’t understand the engineering behind them, does not mean that the answers don’t exist.

I'll answer your questions, but I am going to give you the oppotunity to refine your questions first. Does that sound fair to you?

[Mike K Wenzloff]

...Such as:I have answers to all of the questions you posed in the above posting. As I told you before, just because you don’t understand the engineering behind them, does not mean that the answers don’t exist.

I'll answer your questions, but I am going to give you the oppotunity to refine your questions first. Does that sound fair to you?
Well, seeing how those answers to Paul's questions were never answered either here or there, I will be interested in your answers.

Nor were mine responded to unless they were part of the posts which got the thread killed over there. If so, that aspect could happily remain free in this context, but real answers are always welcome.

And of course, I may need help understanding them, but what the heck, I'm game to trying.

Take care, Mike

[Rob Blaustein]

Although the 'poll' aspect of this thread probably wouldn't provide me with useful information since not enough specifics are given, I am learning much from the spirited exchange of information (although some of the more heated personal discourse gets a little distracting).

[Art Mann]

Paul and others,

Rick did, in fact, provide what I believe is an accurate and complete answer to your question about what you call "strength" which I take to mean rigidity. He used terms that you were not familiar with, such as "bending moment" and "modulus of elasticity". I wouldn't expect you to understand their meaning. However, you should not be so quick to dismiss his reply just because you don't understand it. I will attempt to work this problem using simple math and terms that are understandable to most people.

Suppose you want to glue 2 3/4 X 6 X 12 inch red oak boards together to create a 12 inch square board. The glue manufacturer says that the joint needs to be clamped at a uniform pressure of 200 psi. Simple math says that the number of square inches in the joint is 3/4 * 12 = 9 square inches. Eachs square inch needs to be clamped at 200 pounds, which is the definition of "psi".

Once again, by simple math, the total clamping force required is 9 * 200 = 1800 pounds. If you don't agree with the math so far, stop reading. I don't know how to explain these indesputable facts any better.

Now, you can apply that force in several ways with varying results. You could just apply 1 clamp at 1800 pounds, but there are problems with that. Aside from the fact that an 1800 pound force clamp is hard to come by, the force applied to each square inch of the joint would not be uniform. You already knew that fact inuitively. The uniformity of pressure is is dependant on the stiffness of the objects you are trying to clamp. That is what Rick was getting at when he talked about modulus of elasticity. It turns out that using that concept, and the concept of bending moment, you can actually predict the non-uniformity due to deflection. That was the essence of his calculations. I didn't run the numbers myself, but take his word that they are correct. His (correct) conlusion was that, under the circumstances you described, the board would be stiff enough to produce, more or less, a uniform 200 psi across the glued surface. If you don't agree with the conclusion, I think you should stop, acquire statics and strength of materials texts, learn to apply and make your own calculations and then contradict his assertion. At this point, intuituion isn't worth anything. The world is full of examples of physical properties that are not intuitive but are absolutely true.

You can also apply the 1800 pounds of total force by using 2 clamps at 900 pounds of force, 3 clamps at 600 pound of force or 4 clamps at 450 pounds of force. Even though one 1800 pound clamp might do the job, it is much easier to do a glue-up with 2, 3 or even 4 clamps. The specs on Bessey clamps, which are my preference, say you can apply 400 or maybe 600 pounds of force each without too much difficulty. To achieve this amount of force, you are going to have to torque the handle to pretty near the maximum. Multiple clamps at a lower clamping force will give you the added benefit of applying the force over the whole surface more uniformly. If you were using say 1 inch wide boards, the stiffness would be much less and you would need to use more clamps to achieve a relatively consistent force over the whole surface.

As just about everyone has conceded, you can achieve an acceptable strength joint for some applications using much less clamping force per square inch. I offered one example of getting acceptable results on grain at 45 degrees using only an estimated 25 psi. However, I have repaired several tabletops for people over the years where the glue line joint failed. I can't imagine why someone would want to make a joint under these circumstances that is any less strong than the best they can achieve.

If anyone is still wanting to argue that a poll of mostly amateur woodworkers, rather than the manufacturers own recommendations, is the best source of imformation on the strongest gluing technique, I have nothing else to say.

[Paul Simmel]

Mike,

Thank you.

-=-=-=-

Rick,

Other than to say I had no single person in mind while posting here, and how would I have any way of knowing who’s here or who’s over there, I do not want this thread deleted.

If you could please answer the question, that would be great.

I wont revise, I’ll reiterate the gist of what is important for me to understand:

-=-=-=-

>>> 1800 pounds of pressure per clamp was arrived at by calculating the thickness of the board, (3/4”) with each clamp spanning 12”, by dividing or multiplying (I forget) the pressures of the respective clamps across the 12-inches of ¾” surface. So what I want to know is where in that calculation does it account for the board’s structural strength?

>>> My very non-scientific inner sense tells me that when I am clamping my boards together, the clamping pressures are being transferred along the structural members themselves… that between the 2 clamps the pressures are less in the very middle of my span, but incrementally so. Right next to the clamp, maybe an inch or two, the pressures are going to be greater, etc. Actually, the pressure will be at its greatest right behind the threaded rod on the ball joint. The pressure is transferred from there to the clamp’s metal pad, and through the board incrementally across the span.

>>> I’m sure this can be calculated by someone… short of mini pressure gages placed every inch. ITMT, even though I suspect a certain psi is present, aside from experience and anecdotal accounts, I can’t prove what that pressure is. I don’t know what value to place on the member’s themselves… but I strongly feel that they must be considered in any equation… in the exact same way a cantilever is calculated. I know from experience, that a few feet out with 2 x 12’s 16” o/c is going to support my deck, my second floor, etc., by transferring the load through its structural members to approved uprights right down to the footings.

-=-=-=-

Thank you.

[Mike K Wenzloff]

Paul and others,

Rick did, in fact, provide what I believe is an accurate and complete answer to your question about what you call "strength" which I take to mean rigidity. He used terms that you were not familiar with, such as "bending moment" and "modulus of elasticity". I wouldn't expect you to understand their meaning. ...
Well call me stupid because I cannot find where the two phrases were used by Rick--at least in this thread here.

Go ahead and explain them to me as relates to wood, clamping force, force distribution and fiber crushing. I can understand them.

But as I don't actually work in theoretical realms, tell me how those concepts relate to two pieces of 24" long x 1" thick Cherry I have in my shop right now. One of them is 6" wide, the other ~8.5" wide.

Oh, both boards were picked for their grain and color, but came from different larger boards. One is near QS on one edge, the other picks up at the rift sawn and the grain nearly flattens to a flat sawn aspect. Do those issues even have meaning to the overall issue of clamping force?

I accept that your answer, if given, will be theoretical as these boards are not in front of you, but this does apply to me so please try to be as accurately practical as you can. I need to know what the appropriate clamping force should be, where the two end clamps ought to be, and the distribution of additional clamps if necessary.

And while you are writing your lucid answer, please relate exactly how do I know if I have acheived your recommendations on clamping force [spacing is easy]? I could use a torque wrench but would rather avoid the modifications to my Bessies.

Take care, Mike

[Greg Funk]

I think that people are getting fixated on clamping pressure as the only relevant factor in achieving a strong bond between two pieces of wood. One of the key elements is simply to have a thin layer of adhesive separating the two pieces of wood. As most woodworkers have found it doesn't take a sheepskin on the wall to figure out how hard to squeeze some clamps to achieve a narrow glueline. If the resulting glueline is fat and noticeable then you didn't squeeze hard enough.

While all of this discussion may be important for optimizing joint strength the vast majority of pieces built by hobby woodworkers are greatly over engineered, hence, even if the joints aren't quite optimal they still exceed any reasonable requirements by a wide margin.

If you are interested in a more complete discussion the US forest products laborabtory provides more information than you will ever need: http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch09.pdf. The attached graph shows there is a wide range of conditions yielding optimal joint strength. Note they also mention too much pressure can starve the joint of adhesive and result in weak joint.

Greg

[Allen Grimes]

To Paul Simmel, thanks for making this thread. I have been clamping everything until I either couldn't get it any tighter or the project would start to bend. I will try loosening up a bit and see what kind of results I get.

Its threads like these that keep me coming back to all of the WWing forums, despite the arguments and fights that seem to plague them. SMC is one of my favorites, but there is far too much information out there to only stick to one forum.

Anyway, thanks again Paul

[Howard Acheson]

>> Why is it so hard to believe that a company would do research on their own product and then make recommendations on it's use based on that? It seems people are going to great lengths to avoid acknowledging the obvious.

And, let's not forget that the US Forest Service, Forest Products Labratory has tested adhesives and recommend 200 psi for PVA adhesive. They are not associated with the manufacturers of PVA adhesive. They have no interest in CYA declarations on a subject like this.

The CYA statement of manufacturers of consumer brand adhesives is that it is not to be used for "structural" applications. This would include making glulams used in construction.

[Rick Christopherson]

Paul, thank you for your civil posting. Before I go into specifics, let me first back up and clarify some of the overall concepts in these threads.

Oh, a Postscript is in order: All of my discussions here and in the past are based on using PVA adhesives. Some woodworkers are confusing this information with other glues, where this information should NOT be applied. This is actually part of the reason why so much misinformation exists.

================================================== ================
Cranking the HECK out of Clamps
First off please understand the long history of these discussions and how they got started. Years ago, someone read or heard a manufacturer’s warning about starving a joint by over clamping it. Unfortunately that information was misinterpreted and applied to the wrong situation. The original information was dealing with industrial glue presses, where clamping pressures of several hundred (or even thousand) pounds per square inch of glue surface are possible. People overacted to this news, and mistakenly believed that it applied to standard hand clamps as well.

The original discussions from years ago about cranking a clamp down as hard as you can were not intended to explain “what you should do”, but were originally brought about to explain that if you cranked down your clamps as hard as possible, it would still be impossible to starve the joint (within reasonable limits).

Like so many other discussions, the original intent of that information got lost and people focused on the information without realizing that the intent was no longer there. As a result, some people are mistakenly claiming that you need to crank down your clamps, and forgetting that it was originally stating the you could crank them down without harm.
================================================== ================
Under-Clamping
As a result of the previous concept, many woodworkers that didn’t understand the physics and mathematics behind clamps, over compensated for what they didn’t understand, and began to believe that they should just barely tighten their clamps, for risk of starving the joint. This is actually where Norm Abram comes in, because he was repeating this nearly every week in his show (I believe he has either stopped saying this, or at a minimum, toned down his message in recent years). This was further assisted into popularity because some of the older wood glues should not be over clamped.

When this concept is taken to the extreme, the joint will actually be weakened when the thickness of the glue becomes the primary bond. However, when taken to a lesser extreme, the joint will still remain reasonably strong, but the joint will still be thick enough to result in a visible glue-line. This latter area is where Norm and many other DIY woodworkers reside.
================================================== ================
Somewhere In Between
Unfortunately because of the original history of these discussion, many woodworkers get caught up in the “Us versus Them” philosophy and take the diametrically opposed extremes, without realizing that the proper answer lies somewhere in between. Your poll questions are an example of this--you presented only the two opposite extremes, but did not leave any options for an answer that lies in the middle.

In reality, I believe that most experienced woodworkers lie somewhere in the middle, but when presented with the extremes, they take the side of the extreme that closest suits their norm. There are nevertheless, some woodworkers that do in fact take the extremes as their normal method, and with them, I cannot agree, regardless which extreme they choose.
================================================== ===============
Technical Answers
First off, I believe the 200 psi figure that has been wielded around is not the actual recommendation of the glue manufacturers, and I personally feel this value is too high. (In my previous postings, I never commented on this number, I simply worked through the math using this number as the “given” value.) I don’t recall my past research, but I believe 250 psi is where the risk of joint-starvation begins to be a risk, and therefore, 200 psi is too close for my preference.

I believe the manufacturer actually recommends 100 to 150 psi for an optimal joint pressure, and this is more in tune with my experience as well. So to cater to both sides of this discussion, I will focus on the lower value of this range for the remainder of my discussion (100 psi). this value is well below the “starvation” point, yet high enough to avoid most of the visible glue lines (aside from an improperly prepared joint).

A previous poster has already given you the “Cliff Notes” synopsis of my previous answers from the other forum, so I’m not going to re-hash it. Mike has already stated that he did not understand the information, and I would expect no less from the average woodworker. I don’t expect you to understand the answer, but you did ask the question, and you asked it thinking that it could not be answered. Just because you don’t understand the answer does not mean the answer is either wrong or doesn’t exist.

I am reminded of my days back in college working at a cabinet shop. We had a frequent cabinet design where there were an odd number of doors (3 or 5 doors). The door sizes needed to be equal, so the frame opening sizes needed to vary depending on whether it was a double-door (no stile) or a single door. The shop foreman could only lay out these 3-5 door cabinet frames by trial-and-error. I asked him one day, “Why don’t you just calculate the opening sizes instead of your trial-and-error method?” He responded by saying, “You can’t. There is no equation for calculating it.” Well, using basic Algebra, I jotted down the simple equation for him, and even programmed it into a programmable calculator for him. He still refused to believe it. Because he didn’t understand the basic mathematics behind it, he denied that such a solution could even exist. Even when showed the final result.

This is how you and Mike are approaching this situation. Because you don’t understand the basic mathematics and/or physics behind the clamps, you are taking the stance that it is either voodoo, or simply non-existent.

Whether you consider it voodoo or not, there are even Internet websites where you can enter the parameters from your clamps (such as thread pitch and diameter) and it will kick back to you how much torque you need to apply to your clamps to achieve a reasonable clamping force. Wait! Before you jump on your “horse” and shout me down for making this over-complicated; I wasn’t suggesting that you needed to do this. The only reason I mentioned it is because either you or someone else suggested that it was not possible to know this. Not only is it “known” but you don’t even need to understand the mathematics behind the calculations--the web site will do them for you.

The point is, I’ve already done the research for you. In order to apply a reasonable clamping force to your clamps, you will need to turn the little round handle with 10-20 ft-lbs of torque. To get an understanding of how much strength this will take, go to your local autoparts store and grab a 1” diameter socket and stick it on a torque wrench set to 10 ft-lbs. Can you hold onto the socket and make the torque wrench “click” at 10 ft-lbs? This is what is required to give you the moderate clamping pressure I mentioned above, not the maximum pressure of 200 to 250 psi that was previously discussed.

If you are using a pipe clamp, then these numbers mean that you need to rotate the lever of the handle with 40 to 80 pounds of rotational force on the 3” radius handle. This is more than just “finger tight” that some have suggested. As a matter of fact, this is approaching the knuckle-busting range, and you still are not approaching the starvation point of the joint.
================================================== =======
Follow-up
I know that I did not answer your specific questions in this forum because I already spent the time doing this in the other forum before the thread was deleted. If there is a specific issue that I still have not properly addressed in either of these discussions, please ask it in a polite manner, and I will make my best effort to answer it.

[Kelly C. Hanna]

I laugh everytime I watch Nawm glue anything together....wayyy too much squeeze-out. I tighten just enough to squeeze a bit out.

[Greg Funk]

I laugh everytime I watch Nawm glue anything together....wayyy too much squeeze-out. I tighten just enough to squeeze a bit out.
Why do you laugh? While you may have less cleanup, your method will leave a thicker glue line and a weaker joint.

[Rick Christopherson]

...I cannot find where the two phrases were used by Rick--at least in this thread here.Mike, I know that you have seen my previous response on the other forum, because I read your follow-up posting before the thread was deleted. That thread was deleted because of the follow-ups, not because of my posting.
But as I don't actually work in theoretical realms, tell me how those concepts relate to...... Just because it is a concept that you do not understand does not make it "Theoretical". The information is factual. “Theoretical” means that information has not been proven to science, but it does not mean that it has not been proven to your understanding.

Just because you don’t understand all of the nuances of aircraft flight; does that make a 747 theoretical? Of course not. It simply means that it is a topic beyond your level of knowledge. I don’t understand all of the sections of civil law, but that doesn’t mean I am going to tell an attorney that it is just “theoretical” and hope I don’t get sued.

[Kelly C. Hanna]

Because first of all I think he uses too much glue....second the mess...thrid, I have yet to have a glue joint fail...ever. Bottom line...I think the difference is that the glue amount I use does the job fine without wasting the squeeze-out amount that he does.

Not questioning his technique, just the amount of glue and squeeze-out. I would imagine his pressure is a bit more than mine though.

[Mike K Wenzloff]

Why thank you for the condescension, Rick. Twas the tack in the other place as well--I do have the thread if you would like me to quote you...

I never said, except tongue-in-cheek, that I didn't understand. I think I do understand more than you would be willing to give me credit for, having work in a work environment doing such testing--as stated in the other thread before it poofed. Perhaps you didn't have an opportunity to review my reply to your invictives?

The word theoretical wasn't mis-applied. Your back-peddling on force above indicates you may have come to a better understanding of clamping pressure through these discussions and for that I am happy for you.

It is a point in fact that Titebond does give the 200 lb for hardwood recommendation and 100+ for softwoods. This was Howard's figures which you agreed with. But evidently this isn't a recommendation you truly care to follow. Which is all most of us have argued.

The problem then is, if we are not going to follow those recommendations to the letter, where/when do we stop turning the handle? The answer is "simple." With the "proper" application of glue, perhaps the proper use of cauls, one does not need to approach the values given in the simple formulas as given in this thread.

The fact is, there are many, many factors which apply to a true formulaic expression which cannot be simplified in the above formula.

Take care, Mike

[Gary Keedwell]

No offense to anybody particular, but I'm wondering if I am the only one who thinks this is the most condenscending thread they have ever read.:cool:
Gary K.
PS. please do not respond....I was just thinking out loud:)

[Rick Christopherson]

Mike, If you understand this so well, then why are you attacking me and not my information? If your position is so sound, then why haven't you presented it in all of these discussions.

If there is something incorrect in what I have presented, you have been given ample oppotunity to refute it. To date, no one, including yourself, has given a reason for contradicting the manufacturer's specifications aside from a hunch.

Paul was kind enough to politely ask for answers to his questions. So I am going to do the same with you. Can you please answer why clamping below the manufacturer's specifications is better than following their specifications?

[Paul Simmel]

Rick and Art,

Here is where I loose you, or, Titebond…

If I were to take my 12” long boards and stand them on edge and place a perfectly balanced 200lb I-beam along the top edge (a 200lb clamp with no deflection) you guys are saying that at each 1-inch point there would only be a measurable force of 16.6lbs.

200 / 12 = 16.6

The same 9 * 200lb calculation says that I’d have to place an 1800lb weight across my 12” span in order to comply with manufacturer rec’s… more than 3 cabinet saws! A simple miter joint on a door casing would, per the above, require 400lbs of pressure.

This simply conflicts with just about every cranial sense I possess.

My cranial sense says that laying an even 200 lbs across 12” of glued up edging will give me more than enough pressure… I mean that… more than enough, hence my references to structural members and their stiffness/rigidity/strength, etc.

Though my question was really not addressed, I can see by the responses above why you have not.

I would like to respectfully agree to disagree, and thank you for your responses. There is no possible way I could ever bring myself to use such tremendous forces to my woodworking ventures.

Paul

[Mike K Wenzloff]

Not attacking you, Rick. Wasn't me calling someone a liar. Nor did I write that anyone was incompetent, incapable of understanding, etc. That is what I would call an attack.

What I asked was how to go about clamping something real-world. How to really know how much force my clamps were achieving. Without resorting to torque wrenches. My point which you illustrated is that we really do not know. Nor do you.

Anytime we simply twist a handle as hard as we think we remember from twisting a 1" socket attached to a torques wrench set to 10 lbs in an auto parts store it is a guessing game that is far less than the previously stated benchmark amounts Titebond recommends. Which is what several people in this thread have claimed we all have to do else we are ignorant people, self deluded into thinking we know more than a manufacturer's recommendation. A recommendation which is not only not practical, but with the equipment you and I have in our shopes, is a recommendation which we have no real way of knowing if we achieve it.

What I find interesting is what appears to be a lessening of Titebond's recomendation in your previous post. As I stated, I agree it should be less.

As in the other thread, though, and in agreement with the Titbond guy I quoted, the joins need to be properly prepared. The right amount of glue needs to be applied. The wood needs enough time for the glue to saturate at the cellular level [enough open time/enough glue/and...wait for it...pressure]. But as in his response--the generic glue portion--the clamping recommendations are to account for less than ideal prep. Which includes fresh edges, one which have not oxidized, free from dust, dirt and oils. Woods should be low in moisture content for ideal joins with PVAs. The list goes on.

But supposing those things which we are semi in control of, it takes a modicum of pressure to glue two pieces of wood. Which, by the way, is what I figure twisting a Bessy handle to emulate a 10 ft/lb load using a 1" socket on a torque wrench to be.

Take care, Mike

[Paul Simmel]

Mike,

You had a response from a Titebond guy??? Could you translate or post what was said there?

Thanks

[Tim Sproul]

Everyone's crazy.

We should all go back to the day when glue didn't matter. You had 90 inch wide boards readily available for table tops and no one bothered with a butt joint. Because glue was literally for the horses, you made sure all joinery was mechanical and glue was only to help strengthen the joint. Glue wasn't the main source of strength.

Then all this arguin' would be for naught.

[Andrew Williams]

Not the most condescending thread I have read, but it's up there. I would not mind seeing this thread die.





No offense to anybody particular, but I'm wondering if I am the only one who thinks this is the most condenscending thread they have ever read.:cool:
Gary K.
PS. please do not respond....I was just thinking out loud:)

[Kerry Wright]

My vote was "other", see below.



My high school wood shop teacher conducted a gluing demonstration that left a lasting impression. Eight sets of dado joints, four different gluing techniques, two different clamping "pressures". All joints were dry fit perfect (of course they were, he was the teacher).

On the first set of two he applied way too much glue, one he clamped as tight as he could get (gorilla tight), the other just tight enough to feel just tight (not over tight, just tight) and no he didn't measure the psi applied.
Both clamping pressures achieved excessive and about the same amount of squeeze out.

On the second set the glue was applied to one side only and smoothed out with his finger. Clamps were applied the same as the first set.
Squeeze out was minimal with both clamping pressures.

Third set, glue was applied lightly to both sides smoothed out with his finger and any excess glue removed. Clamping was same as before.
Squeeze out was a little drop every few inches with both clamping pressures, maybe a bit more from the over tight clamp but not much.

Fourth set, glue was dribbled in the joint (same amount as third set) on both sides and clamped without smoothing it out first.
Squeeze out was irregular with some spots excessive and others none at all. This was with both pressures.

All squeeze out from each set was cleaned up immediately after clamping.

The next day each set was given to the class to separate the joint anyway we could. Slamming, pounding, dropping, throwing, beating, hammering (sledges included) proceeded to take place.

Results:
Set one - Both failed miserably. Because there was way too much glue used and the joints were so tight, not all of the excess glue could leave the joint during clamping resulting in a joint that was all glue and no material bonding. As stated previously in this thread, white glue is not a good void type glue.

Set two - Both joints were strong and we couldn't tell much difference between clamping pressures. However, we could see much more separation at the joint than with set three.

Set three - By far the strongest, hardest joint to break apart! The wood broke but the material at the joint did not separate. This was the same for both clamp pressures.

Set four - The one that was clamped with "just tight" pressure failed easily where as the one with "gorilla" pressure faired better but still failed with intermittent material bonding at the joint.

To solidify what he was attempting to get across, he also took a sloppy fitting joint and glued it with method three from above. Results - The boards that were "gorilla" clamped held very well, where as the "just tight" joint held, it had visibly less material bonding than "gorilla tight".

Overall conclusion (and lesson learned): Clamp pressure isn't as important as proper gluing application. Take the time, apply a thin even layer of glue to both sides and clamp. If the joint is a good joint, less pressure will be required to get a superior joint. If the joint is sloppy, more pressure will help. However, as we all know, no glue will make up for poor craftsmanship.

Thank you Mr. Bailey for your insight, your knowledge, and most of all your perseverance in teaching!

[Art Mann]

If I were to take my 12” long boards and stand them on edge and place a perfectly balanced 200lb I-beam along the top edge (a 200lb clamp with no deflection) you guys are saying that at each 1-inch point there would only be a measurable force of 16.6lbs.

200 / 12 = 16.6

Yep, that is exactly what I am saying. To convince yourself this is true, think about 2 sets of bathroom scales with a board between them. Then stand in the middle of the board. Each scale will read half your total weight. Now, think about a 3 legged stool and 3 sets of bathroom scales. Sit down on the stool and notice that each scale will read 1/3 of your weight plus 1/3 the stool weight. Now just imagine you keep adding scales and support points. When you go past 3 legs, you have to start making some assumptions about the coplanarity of the scale surfaces and support structures. That is the same type of assumption as you are making about a flat I beam and a flat jointed board edge. In your example, if you were able to place 12 tiny little sets of scales along the jointed surface of the board between the board and the beam, each one would read 16.6 pounds. Now, if you were to use a Bessey clamp right in the center of 2 12 inch boards that were being clamped together, but instead of making them edge to edge, you inserted 12 tiny equally spaced scales in between the two boards, you would find that all 12 of those little scales would each read somewher close to 16.6 pounds. There would be a small variation in what they would read because of the elasticity of the wood and the bending moment or distance from the point of application of the force.



The same 9 * 200lb calculation says that I’d have to place an 1800lb weight across my 12” span in order to comply with manufacturer rec’s… more than 3 cabinet saws!


That is correct.

Edit: Just remember, if you could somehow configure a Bessey K-body clamp as a screw jack instead of a clamp, you would not have very much trouble at all lifting a cabinet saw off the floor with one easy twist of the wrist.



My cranial sense says that laying an even 200 lbs across 12” of glued up edging will give me more than enough pressure… I mean that… more than enough, hence my references to structural members and their stiffness/rigidity/strength, etc.


If you did that, you would be applying 16.7 psi of force to the glue joint. I would not consider that enough to make a very strong joint. Why don't you do exactly that and then try breaking the board along the glue line while it is clamped up in a wood vise? Just see what happens. I would guess that the board will break along the glue line rather than somewhere else with only 16.7 psi of clamping. That is the real test. Even then, that is not necessarily a reason to use low clamping force. As I said before, I have repaired a lot of old semi antique tables where the top split along the glue line. Perhaps these problems developed because the builder did not use good gluing technique 50 years ago.

[jack duren]

Kinda surprised this topic is on two different forums.

Bottom line is you should apply enough pressure till you can no longer get squeeze out from the joint. For me personally I put around the same torque on all my clamps when combining panels. I simply crank it.

Seems there are a lot that clamp incorrectly no matter which forum your on. Some look to find how many will agree so it can be considered a standard.

Some information on forums is excellent and some information gets too twisted to use:( ....Jack