# Can a clamp really be too tight? Tell me your story.



## Adam_D (Mar 4, 2012)

I'm comfortable with how tight to clamp joints when I'm gluing up-I've developed the feel and have never had any issues with my joints. In addition, I always use scrap between my clamps and work to spread out the pressure and prevent any sort of damage.

However, when I'm teaching someone, they always ask "how tight", and I repeat what I've read about "squishing out all the glue". In my heart of hearts, I don't believe that's even possible.

Can we put this myth to rest? Can anyone offer a story about how they've regretted clamping something too tightly?


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## TheFridge (May 1, 2014)

Look up woodgears.ca glue test

You can't squeeze all the glue out but the joint was noticeably weaker in his tests compared to using a 10lb weight as a clamp.


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## jerryminer (Jun 15, 2014)

Put it to rest? I doubt it. The concept of "glue starvation" from excessive clamping is an old and established myth.

I've done my own tests--and encourage anyone who is concerned with this issue to do their own--and learned that an "over-squished" joint is still stronger than the wood. I don't believe in glue-starvation, or the tooth fairy.


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## knotscott (Feb 27, 2009)

Over the years as I've done many iterations of glue joints, I've learned to try to keep things fairly consistent. I put an ample amount of glue on each board, spread it evenly, and clamp them enough to squeeze a small amount of glue that's consistent down the entire joint. The only times I've felt the need to get really aggressive with the clamping pressure is when the boards don't mate well and I need to force them together….fully jointed and planed boards that are square, very flat, and very straight tend to be pretty very predictable, and mate well. If the wood moves alot or you choose not flatten and square your lumber, then the boards don't mate as consistently and need to be forced, which is ultimately more likely to lead to a weak glue joint.

Cauls help prevent damage on the end of the workpiece.


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## Tony_S (Dec 16, 2009)

damit…


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## Tony_S (Dec 16, 2009)

oops


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## Tony_S (Dec 16, 2009)

25 years.
10 s of thousands of gallons of different brands and types of PVA.
well over a million board feet of hardwood of all descriptions.
Hand, pipe, and bar clamps, pneumatic and hydraulic clamp carriers, vacuum bags…
Pretty much any type of lamination you can think of…edge gluing, face gluing, extreme bent lamination, curved laminated panels….
More idiots than I can count, that damaged clamps.
Working with and discussing this face to face with a pile of damn good woodworkers.

My thoughts on the keep it simple side….it s complete bull********************.

You can t squeeze enough glue out of a joint to the point the joint/bond is weaker than the wood you re gluing.

It shouldn t even be blip on the radar.

With that said, you shouldn t have to use so much pressure that you blow an eyeball out of your head when clamping a joint either.

If you do need to, you should re-examine and improve your joinery techniques.

I still believe in the tooth fairy though.


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## wapakfred (Jul 29, 2011)

It can't be too tight as far as I'm concerned. I tighten them as much as I can, and have never had a problem yet.


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## Tennessee (Jul 8, 2011)

The glue starvation thing is obviously a myth. I clamp hard, with the only caveat being that if I have to clamp THAT hard to get my boards and joints together, there might be something wrong with my boards or my joints. Its a common sense thing.


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## verdesardog (Apr 2, 2011)

Years ago Fine Woodworking magazine did tests and determined that glue squeeze out can not be done enough to weaken a joint. But as others have said if you need to squeeze so much that you might be in doubt your joining techniques need to be addressed.


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## MrRon (Jul 9, 2009)

You should get some squeeze-out. The amount of squeeze-out depends on how much glue you put in the joint. I would apply just enough pressure until the squeeze-out stops. One reason for excessive pressure is if the joint surfaces are not perfectly flat; you are trying to force the wood into contact. if the surfaces are flat, you don't need much pressure to clamp the wood. The glue should be spread very thin on both surfaces, but should cover all surfaces 100%. A clamping pressure of 100 PSI is adequate for low density woods and 250 PSI for high density woods. It doesn't take much to apply 100 PSI.


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## NoThanks (Mar 19, 2014)

If you are weak and only weigh eighty pounds than you might want to risk bursting a blood vessel tightening them, or have my sister do them for you. 
Other than that I have nothing but dry humor to add.


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## ElChe (Sep 28, 2014)

Glue starvation with modern glues has to be a myth. If you starve the joint to me it has more to do with putting in too little glue to begin with. And too much glue is a mess. Basically takes practice to put in just the right amount of glue. I don't overtighten clamps because it is unnecessary with a good fitting joint. And I hate cleaning excessive glue squeeze out. And my sister still beats me arm wrestling.


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## Grandpa (Jan 28, 2011)

If you have to put excessive pressure on a joint in order to close it, then you need to repair that before glue is applied. I have seen clamps tightened so tight they left a huge imprint on the edge of the wood. This wasted some wood but the joint was fine when it dried. I was taught to squeeze the glue out. If you leave a lyer of glue you will see it when you stain. Who wants that?


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## shipwright (Sep 27, 2010)

If by "glue" you mean PVA glue, then I will defer to Tony's expertise and experience. I'd never argue with that.

However if by "glue" you mean all glues then there are certainly places that the "myth" is true and some where it is false. 
Yes, you can clamp an epoxy joint too tight. Best practice in extreme bent laminations with epoxy is either a significantly rough surface or a spacer like a glass cloth to retain sufficient glue in the joint.


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## Tony_S (Dec 16, 2009)

> or a spacer like a glass cloth to retain sufficient glue in the joint.
> - shipwright


That's an interesting suggestion Paul. I've never even considered using something like that. Honestly, I'm not even sure it would be a viable solution(in the world of custom stairs and railing) due to cost, extra labor etc. I can only imagine the ******************** show that would be involved in laying anywhere from 12 to 24 layers of glass cloth in what could be 20 plus foot lengths. lol!
I would assume it would increase the visibility of the glue line as well?
How machinable is it?
Sounds like I've talked myself out of it already…lol. You never know though….with some of the stuff people throw in front of me, you never say never.

Urea based adhesives worked well and achieved what they were intended for(mainly the sheer rigid properties) in the past on hand rail, but it's absolutely murder on tooling, especially high speed steel(moulder heads).
The only time I would typically use it is when certain aspects, or whole stair designs need to be engineered. IE. Integrated headers, commercial applications…In those cases, it's stringers only, no handrail if I can avoid it.

Epoxies….well….mixing epoxies in large quantities by the 'inexperienced' has made for some interesting moments in the past….oh the stories I could tell.

BTW…just for the record, I hate glue manufacturer's and wholesalers sales reps, they're akin to used car salesmen.


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## shipwright (Sep 27, 2010)

I wouldn't recommend the glass cloth solution in your work Tony. It would show and it is tough on tools. Where it comes in handy is in sharply laminated frames in boats where a lot of clamping pressure is required. 
If you need to use epoxy, there's nothing else that will do the job better but if you don't need to there are too many reasons not to to even count. .


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## gargey (Apr 11, 2016)

> Epoxies….well….mixing epoxies in large quantities by the inexperienced has made for some interesting moments in the past….oh the stories I could tell.
> 
> - Tony_S


Cliffhanger


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## KelleyCrafts (May 17, 2016)

+1 for the toothfairy. I glue and clamp until it feels right.


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## ArlinEastman (May 22, 2011)

To tight and a lot of the glue squeezes out and then what is the purpose of gluing.

I just did a nice platter and clamped it to tight the last time and that is where it broke off.


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## Planeman40 (Nov 3, 2010)

YES! A clamp can be too tight.

Back when I was building a homebuilt aircraft I studied all of the FAA papers regarding construction requirements. One of them was a government study regarding gluing of wood. In it were some parameters for clamping pressure which I can't recall, however it did mention that tests proved that too much pressure creates a "glue starved" joint. It squeezes out so much glue the joint begins to lose strength. Now this study was done back in the 1930s, but I think it would be applicable to today. Fortunately, today's glues have improved considerably, but I still believe in not over-tightening. Clamping pressure should be such that it removes excess glue and brings the joint properly together. That is enough.

Planeman


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## Dark_Lightning (Nov 20, 2009)

You won't be doing it with wood, but in the aerospace business, we used glass beads to establish the bond line The standard is .005" diameter. Since the wood has at least that much variation over even a jointed board edge, it is nigh on impossible to starve a glue joint in wood, given the actual surface roughness and the fact of pores. Provided that enough glue was put on to begin with, of course. The reason for beads to establish the bond line is to remove the uncertainty. But then, we didn't clamp it, either (and were using some form of epoxy). Clamping puts stresses into the components, which can break when subjected to launch loads, to relieve that stress.


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## simmo (Nov 23, 2008)

Don't certain modern adhesives have micro balloons to ensure an even layer of adhesive, West system 
chris


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## clin (Sep 3, 2015)

I know the titebond folks have recommended PSI for the best bond. This suggests there is such a thing as too much pressure.

Something to consider for all the folks that say they clamp as tight as possible and never have a problem. While it is easy to get some hundreds of pounds up to even 1,000 lbs (pipe clamp) of pressure from a clamp (exact amount depends on the type of clamp), this spreads out over the clamp area.

Titebound recommends 100-250 PSI (soft to hard wood). Assume a 600 lb clamp, this clamp drops to the minimum of 100 PSI over just 6 sq inches (2" x 3"). And would only be a bit over 2 sq in for the upper limit of 250 PSI.

So sure if you are edge gluing 1X stock and spacing your clamps every few inches, you can exceed the maximum pressure. If you're spacing them much more than 6" apart (again on 1X stock), you probably aren't exceeding the limit.

If you are gluing surfaces wider than a few inches, even with clamps placed immediately next to each other, you likely aren't exceeding the limits.

So, I believe it is likely you can have too much pressure, I also think it is awfully difficult to achieve that in many applications. Thus for many of us, for all practical purposes there no such thing as too much because we don't use enough clamps to achieve that. Obviously this depends on what you are gluing and how many clamps you have available.

I also suspect that too little is a more common mistake than too much pressure.


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