Yellow Glue for my Veneering Project???

[Jon Farley]

Based on some input I've received here on SMC, I feel that I will be able to use regular yellow glue to attach a veneer to an MDF substrate. I was told that since my "veneer" is 3/16" thick that yellow glue would be ok.

Are there any potential problems with this plan? Based on what someone else said, my veneer is too thick to be considered veneer and I could have wood movemnt issues with it. Obviously, if it's all glued down, there is going to be nowhere for it to move. Could it crack?? Help!

[Jamie Buxton]

3/16" is pretty thick for veneer over MDF. The word from the College of the Redwoods (Krenov's program) is that they aim for 3/32" or so when they are resawing.

If you go ahead with this thickeness, you should at least veneer both faces of the MDF. This should reduce warping of the panel when the humidity changes.

[Chris Padilla]

I've seen David Marks use yellow glue on 3/32" veneers all the time. That makes it okay in my book!

Being twice the "recommended" thickness, you could have issues. What is your 'veneer'? If the 'veneer' is fancy maple (birdseye, heavy curl, etc.), you could glue it to a plain maple substrate. That should ensure even movement between both boards since they are the same species.

What is the overall size of the 'veneer' you are using? That could make a difference as well.

[Jon Farley]

Jamie - I will be veneering boths sides of the MDF with red oak that I resawed myself and brought down to the 3/16 thickness with my planer. I could probably get it down to 1/8, but 3/32 would be pushing it.

Chris - the finished size of the veneered table top will be an octagon shape with the main outside dimensions being 22 by 36 with 22 degree tapers at the corners.

[Matt Meiser]

I did some thinner veneer with yellow glue no problem. One thing to think about with yellow glue is assembly time. I used Titebond extend and was cutting it pretty close on 12x24 panels by the time I coated both sides of the substrate.

[Chris Padilla]

Jon, do you plan to vacuum press it? That is probably the most critical aspect of gluing up sizable veneers: even clamping pressure all around. If you need longer working time, you might go the poly glue route (gorilla glue) or the plastic resin glue.

[Barry O'Mahony]

One thing I've always wondered about with the vacuum press and yellow glue is the pressure applied. The theoretical maximum pressure you can get from a vacuum press is 15 psi. If you look at the Franklin International website, they specify a far higher required pressure for Titebond, even for their "cold press veneer glue. I think it's something like 100+ psi. Ain't gonna get that with a vacuum press.

I guess folks use yellow glue in a vacuum press with sucess all the time, even if it is outside the specs for the glue. I suppose in this application, the glue does not need to acheive its maximum adhesive strength.

[Jamie Buxton]

One thing I've always wondered about with the vacuum press and yellow glue is the pressure applied. The theoretical maximum pressure you can get from a vacuum press is 15 psi. If you look at the Franklin International website, they specify a far higher required pressure for Titebond, even for their "cold press veneer glue. I think it's something like 100+ psi. Ain't gonna get that with a vacuum press.

I guess folks use yellow glue in a vacuum press with sucess all the time, even if it is outside the specs for the glue. I suppose in this application, the glue does not need to acheive its maximum adhesive strength.

Barry --

IMHO, woodworkers often overstate the required pressure for gluing. Most wood glues will cure and bond without any applied pressure at all. There are many gluing operations which have no clamping pressure, but which work well. One example is the standard mortise and tenon. You make the tenon so that it slides into the mortise -- that is, there is no pressure being applied on the cheeks of the tenon. However, glue makes this joint very solid.

Clamps are useful in gluing for several reasons. They may

Squeeze glue out for a thinner glue line.
Deform wood to make a thinner glue line.
Hold the wood parts in correct alignment while the glue cures.


If in your gluing operation you don't need any of these aids, you may not need high pressure clamping. Veneering is a fine example. You do need to hold the wood in the correct alignment; veneer will flop all over the place unless you hold it down. However, you only need a few ounces of pressure to hold veneer flat. The trick is that you need that few ounces to be applied everyplace. Put it in only one spot, and the veneer an inch away may be lifting up off the substrate. That's one of the great things about using atmospheric pressure for veneering: it applies pressure everyplace.

[Barry O'Mahony]

Barry --

IMHO, woodworkers often overstate the required pressure for gluing.It's not me making the statement; it's the glue manufacturer itself.

Now I know some glues like epoxy need no clamping pressure whatsoever. But even for their veneer glue, the manufacturer of Titebond specifies very high pressure. Not to say that it won't work anyway, but if you're using yellow glue with a vacuum press, be aware that you're using it outside of manufacturer's specifications.

BTW, with a snug M&T joint, once the wood swells from the water in the glue, I would imagine the joint pressure is pretty high. Would be an interesting experment to try to measure.

[Dave Fifield]

Withdrawn - the most pressure you can get with any vacuum press is, of course, the pressure of the air where you are....which is indeed about 14.7psi.

I use a set of up to 4 homemade mechanical screw presses for my veneering work, which is mostly marquetry. I'm guessing I can easily exceed 100psi with these. I use yellow or white glue most of the time. I recently bought a bottle of that cold press veneer glue to try - let you know how it goes when I do. I haven't needed to do any curvy veneering work yet, but I will oneday I'm sure, and so will make/buy a vacuum press when I need it.

Dave F.

[Doug Shepard]

Jamie - I will be veneering boths sides of the MDF with red oak that I resawed myself and brought down to the 3/16 thickness with my planer. I could probably get it down to 1/8, but 3/32 would be pushing it.
...

You can always run it through the planer again after it's glued on the MDF to bring it down to 3/32 or 1/16".

[Dave Fifield]

Planer? Eeek :eek:

I'd rather use a drum sander on it.

[Lee DeRaud]

Withdrawn - the most pressure you can get with any vacuum press is, of course, the pressure of the air where you are....which is indeed about 14.7psi.

I use a set of up to 4 homemade mechanical screw presses for my veneering work, which is mostly marquetry. I'm guessing I can easily exceed 100psi with these.I'm obviously missing something simple, because I'm having serious problems with these numbers. 100psi works out to seven tons of pressure per square foot. I think I could design a press to generate that pressure, but it sure wouldn't be something you'd want to use in a woodshop.

Looking at the Titebond website, for Titebond III the required clamping pressure is described as "Enough to bring joints tightly together (generally, 100-150 psi for softwoods, 125-175 psi for medium woods and 175-250 psi for hardwoods)"...huh? Anybody got a figure for how much pressure you can get out of a Bessey K-body?

More to the point, vacuum presses work...at about 1/10 the pressure the glue people are asking for. What am I missing here?

[Doug Shepard]

Planer? Eeek :eek:

I'd rather use a drum sander on it.

Me too. That's what my Performax is for. But he didn't mention having anything but the planer. I was just pointing out that while the planer would probably eat his wood getting to 3/32", if it was already glued to the MDF he'd be likely to end up with something other than kindling.

[Jon Farley]

Me too. That's what my Performax is for. But he didn't mention having anything but the planer. I was just pointing out that while the planer would probably eat his wood getting to 3/32", if it was already glued to the MDF he'd be likely to end up with something other than kindling.

Actually, once it's glued to the MDF, it will exceed the max width of my planer, and no I don't have a drum sander. Since I haven't gotten any responses adamantly saying "no don't use 3/16" veneer, you'll have major problems," I'm going to go with it. If between now and the final assembly of this project something changes my mind, it would be no big deal for me to make a new top.

Regarding the planer, I have successfully planed oak down to 1/8 inch, but I was worried about edge gluing these pieces together effectively, so I went with the 3/16 thickness instead.

[Jamie Buxton]

....
Looking at the Titebond website, for Titebond III the required clamping pressure is described as [COLOR=black]"Enough to bring joints tightly together (generally, 100-150 psi for softwoods, 125-175 psi for medium woods and 175-250 psi for hardwoods)"...huh?


"Enough to bring the joints together" is understandable. Why it might take those pressures is difficult to understand. Perhaps Titebond is thinking about some horrible situation in which the wood must be seriously deformed to pull the joint closed. I can't explain it any other way. There's nothing in PVA chemistry which requires pressure to cure.

There's an educational joint one can make. It is called a wiped joint. It takes no clamping pressure, but produces a nice strong glue joint. Make two blocks of wood with glue faces which are perhaps 2"x2". Prepare the glue faces so that they're nice and flat -- maybe you plane a larger piece of wood and cut these two blocks from it. Put a couple drops of any PVA on the glue faces. Push the glue faces together and squooge them around. You've trying to get the glue to wet the entire surface, but mostly trying to encourage any excess to squeeze out the sides. In perhaps ten seconds of squooging, the glue will start setting up, and you won't be able to move the blocks any more. Put the blocks down and go do something else. The next day, try to break the joint. You'll find (well at least I've always found) that the glue bond is stronger than the wood. The key point is that this joint takes no clamping pressure, but it achieves a good bond.

[Lee DeRaud]

Looking at the Titebond website, for Titebond III the required clamping pressure is described as "Enough to bring joints tightly together (generally, 100-150 psi for softwoods, 125-175 psi for medium woods and 175-250 psi for hardwoods)"...huh?"Enough to bring the joints together" is understandable. Why it might take those pressures is difficult to understand. Perhaps Titebond is thinking about some horrible situation in which the wood must be seriously deformed to pull the joint closed. I can't explain it any other way.My thoughts exactly. And if you apply 250psi to any reasonably tight joint, there won't be any glue left in the joint anyway.

[Jamie Buxton]

BTW, with a snug M&T joint, once the wood swells from the water in the glue, I would imagine the joint pressure is pretty high. Would be an interesting experment to try to measure.

I can tell you about one related experiment. Years ago, I got to wondering how much the tenon swells from water in the glue. I was thinking that maybe I should be making my M&T joints with more clearance, to avoid stressing the wood when glue is applied. I made a test "tenon" -- actually just a piece of wood which had been through the thickness planer. It was maybe a half inch thick. I put a micrometer on it, and then painted it with water. The water was a stand-in for the water in the glue. I waited a few minutes until all the liquid had disappeared, and then measured the thickness again. My micrometer can see changes of .001", but it said the tenon's thickness had not changed.

Added in edit.... I've also made a similar measurement on a biscuit -- y'know, the beech things. The ones I measured did change -- I think 10 thou or so. I dunno why biscuits should change and solid wood not -- perhaps it has to do with how the biscuits are manufactured. I have the impression that they are stamped out with a giant press. Maybe it compresses the beech a bit.

[Joe Chritz]

Bessey says 1000 pounds over the jaw surface. Guess I'll need to do some math to find out how much pressure that really is.

I can say I often glue up panels with just a tweek of the handle. A solid shove and the clamp would move some so the pressure is pretty low.

In my non-chemist mind I would say that as long as the surfaces are touching it is all that is needed.

Joe

[Lee DeRaud]

Bessey says 1000 pounds over the jaw surface. Guess I'll need to do some math to find out how much pressure that really is.The jaws are what, maybe 6 square inches? So something in the 150psi range. But I'm guessing it takes cranking the handle with a wrench to get it that tight.

[Barry O'Mahony]

The jaws are what, maybe 6 square inches? So something in the 150psi range. But I'm guessing it takes cranking the handle with a wrench to get it that tight.The area of the jaws are irrelevent. The clamps deliver 1000 pounds each, more or less. The average pressure, in PSI, delivered to the joint is equal to (1000# X number of clamps)/(area of the joint in square inches). The tricky part is getting that distributed evenly. Easy to do in a vacuum press, but a difficult design issue with a clamping system. The pressure tends to be highest directly under the clamps, and decreases as you move away from them. A rule of thumb is that if you go at more than a 45 degree angle away from the clamp, pressure really drops off. So, for instance, if you're edge-joining two boards, if the boards are narrow you need more clamps to keep the pressure even.

For veneering, you want to use thick boards on top of each surface, and cauls which are curved so that clamping pressure is maintained toward the center of the panel. And lots of clamps. Once the panel gets to a certain size, a vacuum press is going to give more clamping pressure than any number of clamps could give.

Of course, in an industrial setting, those big monster presses can easily delivery tons of pressure, spread evenly over a large surface. In this environment, meeting the Titebond specs isn't a problem.

[Dev Emch]

I can tell you about one related experiment. Years ago, I got to wondering how much the tenon swells from water in the glue. I was thinking that maybe I should be making my M&T joints with more clearance, to avoid stressing the wood when glue is applied. I made a test "tenon" -- actually just a piece of wood which had been through the thickness planer. It was maybe a half inch thick. I put a micrometer on it, and then painted it with water. The water was a stand-in for the water in the glue. I waited a few minutes until all the liquid had disappeared, and then measured the thickness again. My micrometer can see changes of .001", but it said the tenon's thickness had not changed.

Added in edit.... I've also made a similar measurement on a biscuit -- y'know, the beech things. The ones I measured did change -- I think 10 thou or so. I dunno why biscuits should change and solid wood not -- perhaps it has to do with how the biscuits are manufactured. I have the impression that they are stamped out with a giant press. Maybe it compresses the beech a bit.

The term biscuit was used first by Lamello and others are not supposed to use it. Porter cable calls them plates and Kaiser of austria calls them Platchens or cookies in english.

Biscuits or cookies or what the term in use is, these items are made from beech which has been compressed in a special press and dried to a very dry condition. When you add water based glue, the biscuit responds quickly and sucks up moisture and swells. That is what they are supposed to do. Likewise, I buy biscuits in boxes of 1000 and as soon as I get them, I put them into an air tight metal tin. Hummidity can cause these to swell so I keep them cool and dry.

A typical clearance for a joint is about 10 thou. So your measurements with the cookies makes perfect sense. A joint that is tighter than 10 thou may have issues with the glue up when the glue swells the joint. Mortise and tenon joints are esp. susceptable. One should often have enough clearance for a glue film between the mortise and the tenon and there should be enough space in the bottom of the joint to take up any excess glue. It also does not hurt to vent the joint. A through tenon is the ulimate ventilated joint. Other examples include a small gash on the side of the tenon which is not visable when the joint comes together. Or you may reduce the width of the joint a mit more to allow the joint to vent. The main strength comes from the long face anyway and the short face is often susceptable to unwanted wood movement. So one of these faces cut short can do double duty to vent the joint.

If your joint is too tight and you cannot vent it, the hydraulic pressure at clamp up can be so great that it blows out the side of the mortise and tenon often on a quite visable side. This would be bad.