glue-up and clamping question

[Michael MacDonald]

is there really a danger of squeezing out too much glue when clamping a glue up? is that possible? I had previously believed that too much clamp pressure might lead to warping, but I hadn't heard until now that squeezing out too much glue was also a possible result...

[Julian Wong]

yes and yes.

squeeze out too much glue and the joint will be starved. I think according to PVA manufacturers, ideal clamping pressure is 200psi which most regular clamping does not exceed anyway. ubless you have a pipe clamp every 2-3 inches and turning down the clamps till your knuckles are blue, you should be fine.

[Lee Schierer]

Over pressurization of a glue joint is really hard to do with hand clamps, unless you get them white knuckle hurt your hand, bow your clamps tight. Most of the time you will crush the wood before you can get enough pressure to squeeze out all the glue to cause glue starvation. The most common cause of glue joint failure is glue starvation by applying too little glue in the first place. Any glue joint should have some squeeze out and if you don't see it, you probably didn't apply enough glue. You should see small, 1/16 to 1/8" dia beads every 1/4 to 3/8" of length on all edges of the joint if the proper amount of glue is applied. Glue running down the surface is just waste.

[Neil Brooks]

I've always heard it ... just the way Lee said it....

[Kent A Bathurst]

FWW did a study of this very question in the recent (1-2 yrs?) past. Conclusion in line with Lee's comments - except they basically said that you simply cannot do it with any kind or any number of hand clamps, even if you are trying to stave the joint (which was their goal, obviously). Pro-shop clamping systems are a different story.

[Howard Acheson]

Most woods will actually deform before you get to the point where you will affect the strength of the adhesive joint.

Our shop had a hydraulic driven panel glue-up device. It exerted about 300 psi along an up to 60 inch glueline.

If you want the strongest and least visiable glue lines, use about 100 psi for soft woods and 200-250 psi for hard woods. To achieve the optimum pressure using 3/4" pipe clamps on 3/4" stock it takes a clamp every 6-8 inches fully tightened down.

[Mike Henderson]

My opinion is that it's essentially impossible to "starve" a joint by clamping it too tight. Although you hear this advice often, I've never seen any test which would substantiate that claim, nor have I ever had a joint come apart because of high clamp pressure. This is with standard PVA glues, urea formaldehyde, or epoxy.

I have had joints "open up" because of insufficient clamp pressure, especially if there was a bow in the joint face, because there was not good wood-to-wood contact. I always err on the side of too much pressure, rather than too little.

I believe I read a blurb put out by Titebond which said the same thing, but I couldn't point you to it now.

Mike

[When I took shop class in high school, we used to clamp boards with pipe clamps and we'd tighten them so tight the wood was seriously deformed where the clamp faces were - and the urea formaldehyde glue held very well. I still have a desk I made 50 years ago in shop class and there's no sign of glue fatigue.]

[Richard Dragin]

There are ways to starve a joint, I don't believe clamping "as tight as you can get it" is one of them.

The only time I am concerned with starving a joint is with an end grain glue up.

[Rick Fisher]

I have been making maple counter tops lately.. Butcher block style, all end grain.

I use a k-body clamp about every 4 inches and tighten with both hands. I start clamping in the middle, then slowly work outwards..

I have had no problem with the glue joints. . I apply the glue with a roller bottle and use a lot..

I really don't see how I could cause a problem this way..

[Ray McCullie]

I believe you can starve a joint, just like you can over tighten a screw. Maybe it'll hold but it won't be as strong in the long run. Just like stripped threads.

If you need to use all your clamping might to get a joint to fit, you need to rework the joint.

[David Cefai]

I agree with most people above that, in pratice, it is impossible to starve a joint when using woodworking glues.

However, wirh epoxy it's a different story. You must take care not to starve the joint. Clamp just tight enough that the wood stays in place (or make loose joints :-) ).

[Will Blick]

Dave, good point.... differrent glues, have different pressure requirements...

But with standard wood glues most of us are accustom to using, its nearly impossible to starve a joint, unless you did not apply enough glue.

Even with a 1" edge to edge panel glue up with hardwood, at 250 psi, if you use pipe clamps at 1000 psi, (avg) , this will require a clamp every 4" to meet the manufacturers reccomendation. Parallel clamps at approx. 500 psi, you need a clamp every 2". Is this mandatory? Not always...if the wood is freshly jointed, and DEAD STRAIGHT, then you can get away with less pressure...otherwise, often you do needed the full stated pressure as Howard mentioned. Its rare anyone can get a board dead straight though, as within 1/2 hour from millling, it will change shape enough to require the full force to overcome the errors.

Increase the boards edge thickiness to 2" , and you must double the clamps above..... which with parallel clamps, they need to be touching each other. Quite extreme. Anyway, this is why its nearly impossible to starve a joint using hand clamps...

OTOH, on a face to face glue up, here is where it becomes nearly impossible to get enough force with hand clamps, as the square inches becomes so great.... Of course at this point, most will start to scream, who needs that much holding power for most ww projects anyway? In most cases, they are right, a face to face glue up rarely has forces applied against the glue line....

HOWEVER, max. holding pressure is not the only reason to use the reccommended pressure.... the other reason is, a "near" invisible glue line....IMO, this is what really makes fine ww differ from construction grade projects.... so, as with everything in ww, one size does not fit all...

luckily, most all glues today are so damn good, one rarely ever needs to worry about failure...unless its a tricky joint, that will be subjected to heavy loads

[Bob Wingard]

The strongest glue joint would involve "intimate" contact between the surfaces, and a layer of glue one molecule thick. If you've ever tried to take an old failed glued joint apart and repair it by adding more glue and reassembling it .. you already know that you can't glue glue to glue. If you have a thick glue joint, that's exactly what you're trying to accomplish. If you spread a layer of glue on two pieces of jointed wood, and think you can squeeze the joint "dry" with the clamps in an average shop, you are grossly exaggerating the abilities of your clamps (and/or your hand strength). In order to "starve" a joint of glue .. it would entail just that .. removing every last molecule of glue .. you aren't going to do that any time soon.

[Will Blick]

Bob, we are saying the same thing.....but I had to re-read the line below 2x till it registered ...so to clarify for newbs...

> If you have a thick glue joint, that's exactly what you're trying to accomplish.


Within the context of what you wrote, yes.... but a thick glue joint is NEVER what you are trying to accomplish.

I always know when I milled the wood straight, applied ample glue and applied the right pressure, the glue line becomes invisible. For me, its mostly about aesthetics, rarely holding force... these glues are so strong, only the most extreme joint, like a thin table top glue up, with 1/4" wood that is 12" wide, with marginal or no added support. (an exaggeration for clarity)

[John Coloccia]

I use the Guttenteit method for adjusting my clamping pressure.

[Bob Wingard]

Bob, we are saying the same thing.....but I had to re-read the line below 2x till it registered ...so to clarify for newbs...

> If you have a thick glue joint, that's exactly what you're trying to accomplish.


Within the context of what you wrote, yes.... but a thick glue joint is NEVER what you are trying to accomplish.

I always know when I milled the wood straight, applied ample glue and applied the right pressure, the glue line becomes invisible. For me, its mostly about aesthetics, rarely holding force... these glues are so strong, only the most extreme joint, like a thin table top glue up, with 1/4" wood that is 12" wide, with marginal or no added support. (an exaggeration for clarity)

RIGHT !! !! !! .. .. .. I never meant to imply that a thick glue line was the goal .. .. .. it was meant to show that a thick glue line consisted of wood to glue to glue to glue to glue to wood bonding, which is inherently weak.

[Mark Woodmark]

There are ways to starve a joint, I don't believe clamping "as tight as you can get it" is one of them.

The only time I am concerned with starving a joint is with an end grain glue up.

End grain should not be considered as a glue joint. It is just not strong enough. wood takes on and expells moisture via it end grain much more so than its long grain with the change in seasons

[Hugh Jardon]

Bob, we are saying the same thing.....but I had to re-read the line below 2x till it registered ...so to clarify for newbs...

> If you have a thick glue joint, that's exactly what you're trying to accomplish.


Within the context of what you wrote, yes.... but a thick glue joint is NEVER what you are trying to accomplish.

I always know when I milled the wood straight, applied ample glue and applied the right pressure, the glue line becomes invisible. For me, its mostly about aesthetics, rarely holding force... these glues are so strong, only the most extreme joint, like a thin table top glue up, with 1/4" wood that is 12" wide, with marginal or no added support. (an exaggeration for clarity)

Newb or otherwise, no clarification needed. It's perfectly clear that glue is intended to bond wood to wood. Not to form a mass of itself like Bondo. It's glue, not filler.

I was always taught "Just enough". Both words being operative. But then it takes experience to correctly judge that amount. Experience of course aids good judgement. Experience itself being borne of bad judgement...

[Michael MacDonald]

thanks for all the comments. heck of a lot of knowledge out there.

This is quite a relief--I was twisting the clamps a little tighter than I normally do for some stair treads of QS white oak, using TB II glue. otherwise, the glue-up was text book.

And then I saw a NYW where Norm drops a hint about squeezing out too much glue. So I started to get worried... I can tell that I was nowhere near causing a problem based on these comments...