Glue Joint Clamping Pressure

[Rob Will]

Currently working on an oak table top. This is sort of an off-the-wall question but is there a particular pressure (psi) that should be applied to a Titebond glue line?

I have some really heavy clamps and don't want to "overclamp" this project. (3/4" thick top)

If I use adjacent 12" wide quarter sawn boards (book matched), would this make a nice top? Each half of the expanding table is 24" x 48".

I am a beginner and appreciate any thoughts you care to add.

Rob

[Barry O'Mahony]

Rob,

Titebond recommends 175-250 psi for hardwoods. A clamp like a Bessey K-body is rated to apply 1000 lbs of pressure. So if you want 175 psi along the joint, that's one clamp every 7-8 inches.

I bet there are many, many times when PVA glue is used and the clamping pressue is nowhere near the manufacturer-recommended range. Seems to work most of the time, anyway. It is highly unlikely that you will "overclamp" the joint, although there may be some local deformation of the wood where the clamps contact it. This can be dealt with by using cushioning cauls, using clamps with large contact areas, or trimming off the deformed area when done.

[Mark Singer]

I usually have clamps about 8 to 10 inches apart. Do a dry test and make sure the boards fit well. A little hand planing makes a difference, You can remove the jointer scallop texture and really fit the boards to each other by planind just a little. Then less pressure is needed. Never try to make a bad fit better with more pressure or clamps. Apply glue to both mating surfaces...

[Dennis Peacock]

Mark has ya covered pretty good here.....but I'll add one more thing:

Never squeeze a glue joint too tightly. You can force a glue joint to be glue starved...or make it a fairly dry glue joint. I like to apply enough pressure to hold the joints together with a "snug" fit.....I used to force boards together to close those little gaps that I couldn't stand. I've since...learned better. :rolleyes: :D

[Frank Pellow]

I usually have clamps about 8 to 10 inches apart. Do a dry test and make sure the boards fit well. A little hand planing makes a difference, You can remove the jointer scallop texture and really fit the boards to each other by planind just a little. Then less pressure is needed. Never try to make a bad fit better with more pressure or clamps. Apply glue to both mating surfaces...
Good advice Mark. You recommend one thing that I never knew (in spite of the many many joints I have glued together) and that is to apply glue to both mating surfaces. Why should this be done?

[Jesse Cloud]

Good advice above on clamping. One bit of advice I would offer (that you didn't ask for) is to rethink using 12 inch wide boards. Its hard to come by wood that wide and will increase your cost substantially, and probably increase the likelihood that the table top will warp. Consider using three or four boards to get to 24 inches. Pay particular attention when you glue them together to get them flat in relation to each other. If needed, try c-clamps on the edge to force flatness (use a bit of wax paper and wood scraps between the clamp and your top to ensure you don't glue the clamp to the top. A minute of care at glue up time can save an hour on the sander!

[Wayne Gauthier]

My question is: how are you measuring the PSI to get the 175# + PSI.

I clamp till the glue squeezes out some, but not enough so that all the glue is out.

[David Abel]

My question is: how are you measuring the PSI to get the 175# + PSI.

I clamp till the glue squeezes out some, but not enough so that all the glue is out.

You CAN'T squeeze out ALL the glue. <g>

[Steve Schoene]

One bit of advice I would offer (that you didn't ask for) is to rethink using 12 inch wide boards. Its hard to come by wood that wide and will increase your cost substantially, and probably increase the likelihood that the table top will warp. !

I'll take the contrary view here. The visual impact of chopping up the surface into more boards would be significant, and with quartersawn wood, the warp risk is low to begin with, assuming that the lumber is properly dry.

[Barry O'Mahony]

Never squeeze a glue joint too tightly. Based on the manufacturer recommendations from Titebond, it is very difficult to squeeze the joint too tightly. 250 PSI is alot of pressure.

[Lee Schierer]

When I glue up boards I apply a thin bead of glue from the bottle. Then I spread that bead over the entire surface with an old toothbrush. Leave a thin coating. Toss the glue coated toothbrush in a small can of water and it will be ready to go the next time you need to spread glue. The entire surface should be wet with glue and not look like it has dry spots. I clamp the boards tight enough to get some squeeze out in the form of small droplets on each side of the boards. If the droplets turn into runs or create puddles on your work surface then you used too much glue. If you didn't see any droplets and you have lots of pressure your joint may fail. Take it apart before the glue sets up and apply a little more glue.

After about the second or third glue up you do you will get the hang of how much glue to apply.

If your clamps are crushing the wood on the edges then you might be applying too much pressure. I always use thin strips of scrap wood to protect my finished edges from clamp damage.

[Travis Porter]

I read or saw somewhere to tighten it with the hand you don't use. If you are right handed tighten it down with your left.

[Rob Will]

My question is: how are you measuring the PSI to get the 175# + PSI.

I clamp till the glue squeezes out some, but not enough so that all the glue is out.

Since I am a beginner and have litte feel for exactly how tight tight is, I would probably put one of my clamps on the bathroom scales(?). This would at least get me in the range that you guys are talking about (obviously divided by the area being clamped). Oops, my bathroom scales won't read 6000 lbs. I guess I'll use a couple of 2x4s and a block to set the clamp at...let's say a 10:1 ratio away from the scales. Another method might be to screw a pressure gauge into the piston end of a hydraulic cylinder (of known internal diameter), put it in a squeeze with the clamp and calculate the clamping force based on the gauge reading(?). Oh well, we'll figure something out.

I literally have a pickup truck load of Jorgensen 7000 series I-beam clamps (48 pcs.) so I probably do need to use some moderation. Thanks for the rules of thumb.

Rob

[Rob Will]

I'll take the contrary view here. The visual impact of chopping up the surface into more boards would be significant, and with quartersawn wood, the warp risk is low to begin with, assuming that the lumber is properly dry.

Yes the wood was cut from a very large, clear log. There are 8 adjacent boards that are quite wide and truly quarter sawn. They have been kept together. Sort of wierd I guess but I just wondered if it will work :confused: .

Rob

[Rob Will]

The only extra toothbrush that I have is my wife's.
Great idea!

Rob

[Rob Will]

Good advice above on clamping. One bit of advice I would offer (that you didn't ask for) is to rethink using 12 inch wide boards. Its hard to come by wood that wide and will increase your cost substantially, and probably increase the likelihood that the table top will warp. Consider using three or four boards to get to 24 inches. Pay particular attention when you glue them together to get them flat in relation to each other. If needed, try c-clamps on the edge to force flatness (use a bit of wax paper and wood scraps between the clamp and your top to ensure you don't glue the clamp to the top. A minute of care at glue up time can save an hour on the sander!

I like the wax paper trick with the c-clamps. We do have some unusualy wide boards to work with.:)