I've seen completely opposite opinions. On the one hand I have seen "scientific" perspectives saying that even a dense set of the best clamps can barely supply the "optimal" clamping pressure.
On the other hand, I see the woodworking shows warning about not clamping too tight so as to prevent glue squeezout and starving the joint of glue.
So who is right the "scientists" or the "practitioners" or both?
If I am not mistaken, titebond recommends 100 to 150 psi, this makes good tight joints that won't creep, with a lot of clamps this is not too hard to get close to on edge gluing, but for laminating larger items it would be almost impossible without spending a lot on equipment.
Get your fitting as close as possible and apply the most amount of pressure you can, without damaging your work or clamps, works for me.
basilisk
The proof is in the pudding ...
Things to consider. The best joint contains 2 mating surfaces that are perfectly flat.
Clamps sole purpose are to hold the pieces in alignment until the glue cures.
Clamps are often used to squeeze an ill fitting joint into submission. See above comment about the best joints.
You can use masking tape to clamp a properly fitting joint.
You will never starve a joint of glue by clamping too tightly. Glue starvation is a condition that is caused by not applying glue properly in the first place. Running a bead of glue down the edge or surface of a board and not spreading the glue over the entire surface is the first step to glue starvation. A thin glue line is the best. Tightly clamping an ill fitting joint to close the gap will aid in a better bond at the joint, it creates a thinner glue line, unfortunately an ill fitting joint may appear to fail as the wood splits "next to" the actual glue line.
I disagree. Tests have shown that PVA glue joints are stronger when clamped tightly than when just "held in alignment". Whether that added strength is actually necessary is a different question.
Agreed.
Chris
Is that because it takes pressure to minimize the glue (joint) width? Just holding the boards in alignment may cause there to be too much glue in the joint.
But you sure can warp the boards.
Waaaa?
No, you need to clamp.
There is lots of practical info published on this for PVA glues (Titebond wood glue, etc.). FWW magazine had a study a while back. a few hundred lbs clamping force is what is needed. The most important things the study show is that various types of clamps have widely different capacities to generate clamping force. The modern parallel clamps can get to a thousand + pounds. Thin bar clamps can struggle to get to 150 lbs. Pipe clamps IIRC can also create quite some force. Strangely they report the pistol grip clamps also generate huge amounts of force but I just can't believe it. I just use them for positioning and lite work.
So use good clamps and there is no need to overtighten. Clamp until you see squeeze and give it another little twist just to be sure. Trust me, masking tape ain't gonna do it with PVA glue.
If you are edge glu> I've seen completely opposite opinions.
Excellent description and practice.
Belong to FWW online?
-------------------------------------------- Depends.
If you are using typical wood working glues like TiteBond II, then high clamping pressures are suggested by the manufacturer.
OTOH, if you are using quality epoxy, then only a minimum amount of clamping pressure is required to hold pieces in place while epoxy cures.
Different horses for different courses.
Lew
Well you are certainly welcome to disagree but I have on many many occasions not used clamps on glue ups and the joints have never failed. Including the panel glue up that was clamped, but not to my melamine TS extension table. Squeeze out glued the panel to the laminate and the laminate broke after jerking the panel up to free it from the TS. Squeezing glue does not add to its strength.
If you have tight fitting joints, hardly any pressure is needed. If not, no pressure is enough :-).
I've seen antique furniture with "rubbed" joint corner blocks that have lasted and lasted and ...
And don't overdo the glue. A thin even coat on each piece, thin enough that you can see the grain through the wet glue, is the best. But I've often gotten away with only coating one piece.
On Wed, 10 Mar 2010 08:17:24 -0600, the infamous Swingman scrawled the following:
You clamp pudding? Um, are we talkin' shaky puddin' here, Swingy? I clamp onto that when it's around, too. (Go, Gator!)
-- There is no such thing as limits to growth, because there are no limits to the human capacity for intelligence, imagination, and wonder. -- Ronald Reagan
Thanks to you and others for the very helpful explanation...
Yeah - I actually read that article once upon a time but then last night I was watching the weekly online version of New Yankee Workshop classics and Norm was talking about not clamping too tight to avoid squeezout... so I just wanted to get some additional perspective on these seemingly conflicting viewpoints...
I guess I tend to believe the science, but on the other hand real life doesn't always follow theory ;)
Is higher clamping pressure bad for epoxy or just unnecessary?
What about for the various polyurethane glues?
High clamoing pressure starves the joint of epoxy needed for a good joint.
I chose not to comment on that garbage other than to say it is overpriced and under peckered.
Lew
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.