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

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Forum topic by Adam D posted 01-17-2015 02:50 AM 2318 views 0 times favorited 23 replies Add to Favorites Watch
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Adam D

103 posts in 2449 days

01-17-2015 02:50 AM

Topic tags/keywords: glue clamp joint

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?

-- Adam, Rochester NY

23 replies so far

View TheFridge's profile


10502 posts in 1661 days

#1 posted 01-17-2015 03:24 AM

Look up 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.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View jerryminer's profile


944 posts in 1617 days

#2 posted 01-17-2015 08:36 AM

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.

-- Jerry, making sawdust professionally since 1976

View knotscott's profile


8140 posts in 3551 days

#3 posted 01-17-2015 11:12 AM

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.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View Tony_S's profile


942 posts in 3258 days

#4 posted 01-17-2015 12:21 PM


-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View Tony_S's profile


942 posts in 3258 days

#5 posted 01-17-2015 12:23 PM


-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View Tony_S's profile


942 posts in 3258 days

#6 posted 01-17-2015 12:24 PM

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 bullshit.

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.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View Fred Hargis's profile

Fred Hargis

5143 posts in 2669 days

#7 posted 01-17-2015 12:58 PM

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.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Tennessee's profile


2889 posts in 2690 days

#8 posted 01-17-2015 03:10 PM

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.

-- Tsunami Guitars and Custom Woodworking, Cleveland, TN

View verdesardog's profile


171 posts in 2787 days

#9 posted 01-17-2015 04:52 PM

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.

-- .. heyoka ..

View MrRon's profile


5141 posts in 3419 days

#10 posted 01-17-2015 04:59 PM

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.

View NoThanks's profile


798 posts in 1704 days

#11 posted 01-17-2015 05:15 PM

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.

-- Because I'm gone, that's why!

View ElChe's profile


630 posts in 1512 days

#12 posted 01-17-2015 05:23 PM

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.

-- Tom - Measure twice cut once. Then measure again. Curse. Fudge.

View Grandpa's profile


3261 posts in 2851 days

#13 posted 01-17-2015 11:27 PM

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?

View shipwright's profile


8132 posts in 2973 days

#14 posted 01-18-2015 02:35 AM

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.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View Tony_S's profile


942 posts in 3258 days

#15 posted 01-18-2015 01:42 PM

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 shit 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.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

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