Taunton article on glue ups

[bobscarle]

I have been reading an interesting article on the Taunton site about glue ups. It appears that the amount of clamp pressure applied to a joint when doing glue ups is normally nowhere near enough!

The common thought is that just enough pressure to "Bring the Joint Together" may produce a joint that is weaker than it could be. Here is a link to the article, I don't think you have to subscribe to read it as I am doing so without being logged in.

http://www.finewoodworking.com/item/27119/clamps-the-secrets-to-success

Bob

 

[BTR]

I also read this yesterday and have you seen the pressure on some woods 1200psi for sugar maple :shock:

 

[eoinsgaff]

Hmmm, the science sounds plausible but I wonder how much of this is driven by a need to encourage the sale of more/better clamps.

FWW can be a very influential magazine - for example I have a feeling that Lie Nielsen have a lot to be thankful for.

Eoin

 

[AndyT]

Like Eoin said.

Surely the only test that really matters is whether the things you make fail in use. I've made a wide variety of stuff with various clamps or none and I've never had any of it fall apart. I'm not going to start worrying now.

I'm especially fond of the old-style wooden handscrews that I can make for myself, but the mags don't get paid to advertise them!

 

[Chems]

Hmmm, the science sounds plausible but I wonder how much of this is driven by a need to encourage the sale of more/better clamps.

FWW can be a very influential magazine - for example I have a feeling that Lie Nielsen have a lot to be thankful for.

Eoin

I agree, I don't use massive amounts of pressure and I haven't had any panels fall apart.

 

[ByronBlack]

I'd worry with that amount of pressue that you would force too much of the glue out resulting in a poor/dry joint. Like the rest of you, I've only used moderate pressure using very cheap EDIT: clamps, and I've never had a failed joint.

 

[Chems]

I'd worry with that amount of pressue that you would force too much of the glue out resulting in a poor/dry joint. Like the rest of you, I've only used moderate pressure using very cheap clamps, and I've never had a failed joint.

I take it thats what you meant Bryon, I totally agree, when I started out I broke 3 clamps trying to over pressure the joint, theres no need for it.

 

[ByronBlack]

I'd worry with that amount of pressue that you would force too much of the glue out resulting in a poor/dry joint. Like the rest of you, I've only used moderate pressure using very cheap clamps, and I've never had a failed joint.

I take it thats what you meant Bryon, I totally agree, when I started out I broke 3 clamps trying to over pressure the joint, theres no need for it.

Aye - I meant clamps, not sure why I wrote joints, been a stressful day today..

 

[woodbloke]

This is an interesting one. Couple of things spring to mind, first and foremost, why then is it recommended that no cramps are applied to drawers once the joints have pulled up? Second and foremost, too many cramps could pull the project out of true?
First question probably answers the second #-o - Rob

 

[Henning]

We will all be needing these soon:

http://www.stylefeeder.com/i/cr5nrsq1/U ... -Ur153hy12

For the kind of clamping pressure promoted in that article.

Article does seem to be well founded though, but i do think there's a lot of difference between good enough for regular use and absolutely ultimate when it comes to glue joints.

 

[andy king]

And if the 'amount of pressure applied may not be enough' is valid, exactly how many clamps are needed when doing a rub joint for example? Well that'll be none then! :lol:
So where is the 'not enough pressure' argument there? In the case of 'proper' joints, M&T etc I was taught that a good fitting joint should be able to be assembled with hand pressure, and when glued, the clamps simply hold things in place so the shoulders come up tight, and the piece remains square.
No excessive pressure is needed - simply enough to show squeeze out on the joint as the shoulders come up tightly.

cheers,
Andy

 

[gerrybhoy70]

Just my tuppence worth having just come through the college work for all this.
If we need to put more clamp pressure on, then surely we'd be getting taught this and not just to grip til squeeze out and hold square (as Andy says).
Plus, even with packers between clamps and workpiece, surely higher pressures will cause the packers to mark the work - defeating the purpose of using them in the first place.

So whether its clamps, cramps or bands being used, I'd still go along with the theory of just enough is more than enough.

Gerry

 

[yetloh]

I suspect it may vary with the type of glue. PVA or its variants seem to near universal in the US and I am sure I have read that they are pressure sensitive glues. But is true of all types of glue?

Jim

 

[xy mosian]

Does this mean there is hardly any point putting glue on the faces of a tenon? Only on the shoulders, for that is where the clamping pressure is.

xy

 

[bobscarle]

Certainly an interesting and well written article, not sure I totally agree with it though. Seems to argue that unless you force the glue into or between the wood fibres, the joint will be weaker. Therefore, close grained woods such as maple need very high clamping pressures, whilst softwoods need considerably less. Makes a degree of sense.

Also worth noting is the number of cramps used, far more than I have ever used on a glue up.

Bob

 

[Sgian Dubh]

Just my tuppence worth having just come through the college work for all this.
If we need to put more clamp pressure on, then surely we'd be getting taught this and not just to grip til squeeze out and hold square Gerry

If you had studied under me Gerry, I would have told you to apply as much pressure as you reasonably could without bursting blood vessels in your neck, ie, tighten up very firmly.

Applying firm pressure matters primarily in situations where you can actually put pressure on glue joints where the two adjacent faces are glued together, eg, edge joinery in panel glue ups-- these should be cramped together as firmly as reasonably possible using, for example, sash cramps spaced about 6-8" apart and alternated either side of the panel. Here you are looking to maximise the effective gluing of long grain to long grain.

If you are assembling a mortised and tenoned framework your clamps are there to pull the frame up tight at the shoulder line and get it square and just need to be tightened up enough to fully close the joint-- you can't effectively apply pressure to the outside surfaces of the morticed member to close the mortice cheeks tighter on to the tenon faces to maximise long grain to long grain gluing effectiveness. To maximise the glue bond here you have to rely on accurate joinery, and also remember there are somewhat different directional forces that act on M&Ts than act on panel edge joinery.

I think people forget this aspect of the recommendation by glue manufacturers to apply very firm pressure, ie, that it really only applies in circumstances like the one I described, such as the aforementioned panel glue-ups. They get a bit too excited about the wrong thing thinking this advice applies to all sorts of glue-ups where the recommendation really cannot be applied in any practical manner. Slainte.

 

[gerrybhoy70]

Many thanks for the advice Sgian. Always welcomed as still learning as I go along.

Will be kept firmly in mind for future use.

Could be that the colleges etc are teaching low pressure clamping to save wear on their tools & equipment, thus allowing for longer lifespan.
Just a thought, seeing as they all claim to be skint at the minute.

Gerry

 

[AndyT]

Does this mean there is hardly any point putting glue on the faces of a tenon? Only on the shoulders, for that is where the clamping pressure is.

xy

That's the logic of the article, yes - but we all know from collective experience that it's nonsense - therefore the logic of the article is flawed.

 

[Boatfixer]

Surely it all depends on the glue as well? I know that West epoxy warn against clamping too tight in their instruction manuals.

 

[Sgian Dubh]

It does Boatfixer. Epoxy resins, I think I'm correct in saying, are the only example of common glues used for wood that actually create a stronger bond with less pressure. All the other ones, even hide glue, bond better with high pressure. Hide glue is interesting because it's sometimes used in the form of rub joints, but even here, in panel glue ups for example, this glue bonds better with good pressure applied after the initial glue grab after rubbing.

If there are doubts about this amongst vistors here, then a visit to Franklin's website and a read of their technical specifications should reassure them that high pressure is appropriate. This American company isn't going to knowingly put out misinformation about the application and use of its own products, particularly as they spend hundreds of thousands of dollars on research into those products. The last thing a company like this needs is user complaints because of glue failure and a difficult to use product. They surely have a very good idea how their adhesives work best, in what conditions, and how they should be used, ie, applied, the parts brought together, clamped up, ideal temperature, etc. Slainte.