# Failure of glue joints at the ends of tables



## Purrmaster (Sep 1, 2012)

Hi all.

There's a problem I've been consistently running into and I would like to seek some opinions.

On most if not all of the tables I've made I noticed a tendency for the glue joints in the table top to crack. It always happens at the end grain sides of the table. It usually takes a couple of months but it will happen.

I've actually seen similar results on many of the large panels I've glued up.

My assumption is that is being caused by wood movement in reaction to moisture changes. Which means I'm not designing properly for wood movement.

When I make a table I typically do it like so:

Make a wider panel by gluing together thinner boards. Usually to a width of 12 inches, since that's why my planer can handle.

I then make aprons for the table. I fasten the aprons to the underside with pocket hole screws and glue. Then I attach the legs to the underside with pocket hole screws and glue. Usually I fasten some battens to the underside as well. Sometimes with just screws and sometimes with both screws and glue.

Everything seems stable for a month or two later I notice the glue joint breaking and the boards at the end separating. It doesn't seem to matter what finish I use (lacquer, shellac, varnishes).

So…. what am I doing wrong? I assume I'm messing up several somethings.

Thanks!


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## Unknowncraftsman (Jun 23, 2013)

Most likely cause is your edge joint needs correction, here is my suggestion before you glue up your next edge joint clamp one side near the end does the opposite side open up?
Your jointer maybe giving you the opposite of a spring joint? Not good.
Sorry to sound like a buzz kill and I am not putting down your technique or machines?
A tru jointed edge can be tricky to get .Kinda like perfect miters.Hope this helps.Aj


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## wseand (Jan 27, 2010)

If I were to guess I would say it could be one or a number of things.

1 Glue didn't cure properly
2 Not enough pressure when it was clamped together or not properly clamped. Too much pressure.
3 Not enough glue.
4 The ends weren't completely square.
5 Bad Glue/Wrong Glue.
6 Sometimes to wide of boards glued together can cause you trouble, I rarely glue pieces wider than 8 inches together. Usually 6 to 6.5 inches. I will glue two 13 inch pieces together but it was made from two 6.5 inches, if that makes sense. 
7 I never secure the aprons to the top tightly, the top should be able to move slightly separate from the aprons. A little wiggle as it were.

Without knowing more about your gluing process I can't be sure.

Hope that helps….BILL


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## longgone (May 5, 2009)

Your top boards need to have a tight fit when you do a dry fit so that you see absolutely no gaps. You also need glue on all of both surfaces so the joint is not starved of glue…and then do not apply too much pressure when clamping or you will squeeze out too much glue and it will not penetrate into the grain enough..

Gluing your aprons to the table top and then gluing your legs to the top is not a good idea. Your best bet would be to fasten and glue your aprons and legs together first. You need to let your table top have room to expand across the grain and if it is glued to the aprons and legs it will cause problems such as warping and/or stressing the glue joints. 
The top is expanding and the apron and legs expand in a different direction
There are different ways to fasten a top to the base and they all need expansion room in the slots where they connect.


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## RogerInColorado (Jan 18, 2013)

You opened with stating the glue joints were failing. I keep reading that modern glues are stronger than the materials they bond. That's not what you say you are experiencing. All of the other responses are correct, but If I were you, I'd also make a glue change. The only times I have ever had a glue joint fail, I had a BUNCH of glue joints fail. I got rid of all the glue on my shelf that I had bought at about the same time and chalked it up to a bad batch. Also, all glue brands are not created equal.


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## pintodeluxe (Sep 12, 2010)

Any part that is glued or screwed across the grain will eventually cause problems. Pocket holes don't allow enough room for the table to move across its width. I suggest figure 8 fasteners, as they make a solid connection, yet allow the wood to move. 
Breadboard ends are another option. They are usually glued only at the center, and are pegged or screwed at both ends through slotted holes.


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## Purrmaster (Sep 1, 2012)

Thanks for the responses. As much as I'd love to blame the glue or the wood I'm certain the fault lies with me. I've used all three types of Titebond, gorilla glue, and elmer's yellow glue.

I actually didn't know you could put too much clamping pressure on but that does make sense. I can almost never get the boards to dry fit tightly. This, once again, is almost certainly my fault. So I often have to put extra clamping pressure on (sometimes a lot of extra) to push the board edges together. The results (once run through the planer) *look* solid but they may not be.

I too have read that glue is stronger than wood. I think that's true, under perfect conditions.

Since the glue joint failure is almost always at the end grain side of things would that change the prognosis at all?


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## exelectrician (Oct 3, 2011)

I put biscuits every 9" when doing edge glue up's I also have an edge joint router bit that I used once on a raised panel, the joint made with this bit is totally reliable, but eats up valuable width in the wood.


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## jinkyjock (Feb 2, 2014)

Purrmaster,
as* exelectrician* said, biscuits are good for extra bite.
Or if you have a grooving router bit and glue in a slip-feather full length.
However, if you cannot dry-fit edges with *minimal* pressure then you need to go back to your Jointer.
Sometimes with larger tops prior to glue-up, dry-clamp and leave in clamps under light pressure for a couple of days.
Then fine tune and proceed with glue-up.
Also, are you alternating boards for grain direction to balance movemnt. 
Check rings in end-grain.
Good luck.
Cheers, Jinky (James).


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## Tony_S (Dec 16, 2009)

> I actually didn t know you could put too much clamping pressure on but that does make sense.


I've heard this mentioned over and over,here and in the past and with all due respect to those who claim it's possible to 'squeeze all the glue out' or 'squeeze too much glue out' by over tightening….it's not. It's a woodworking fallacy.
But, with that said, if all of your material is both sound and stable, as well as being prepped as it should be, using proper mill-work techniques…..there should be absolutely no reason to apply anymore pressure than you can with a firm twist with your bare hand regardless of the size of the panel.



> I can almost never get the boards to dry fit tightly. This, once again, is almost certainly my fault. So I often have to put extra clamping pressure on (sometimes a lot of extra) to push the board edges together.
> - Purrmaster


You answered your own question right here. Your material isn't prepped properly.
A simple rule of thumb I teach all my apprentices….lay out your full panel as it should be before glue up. If you can't close any gaps with simple hand pressure(without opening any others) there is a strong possibility of failure sometime in the (near)future. Don't argue with wood….it always wins.

Proper edge jointing CAN be a real bear.
First course of action would be to make sure your jointer is set up properly, including sharp blades. If it isn't, your setting yourself up for frustration and failure.
Once you've established that, proper jointing technique comes a lot more easily, but even that can be a source of frustration for many.
Once you understand how a jointer should be properly set and refine your technique….you'll wonder what the fuss was about.


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## JayG46 (Apr 24, 2013)

I think the problem lies in the fact that you are attaching the top to the aprons with glue. If I understand correctly, the cracking is happening nearest the end grain, where your shorter aprons are attached perpendicular to the grain to on the top. The boards that make up the top want to expand and contract across their width but can't do so freely since they are restrained by the screwed and glued aprons. Unfortunately, they are going to move anyway, and that force is enough to separate the fibers within the boards from each other, creating cracks.

I haven't had problems attaching table tops to bases with pocket screws, but pintodeluxe's suggestion of figure eight fasteners is probably a good one.


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## TheWoodenOyster (Feb 6, 2013)

First off, perfectly straight edges are tough to get off the jointer, so don't feel bad. I have been at this pretty hard for 2 or 3 years, and I still have to work pretty hard to get good glue joints off the jointer. Not easy.

My .02 on your problem is that I would start using boards that are not as wide. 13 inches wide is really wide when it comes to stability. As suggested above, try using boards that aren't so wide, maybe 4 to 6 inches. Think about it this way, the more glue you have in a panel, the more stable it is.


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## Purrmaster (Sep 1, 2012)

Once again, thanks for the responses. Very enlightening.

Yes, the cracking is happening nearest the end grain. Once in a great while I've seen joint failure in the middle of a panel made of up thinner boards but I think those are one off scenarios where I goofed something. But the cracking at the end grain is chronic. I noticed it on 3 tables I had made the other day.

And yes, the short aprons are glued and pocket hole screwed across the grain of the panel. I had wondered if that was a stupid move to make. I used glue as well as screws because I figured I'd have a stronger table in the end. Also, the Kreg jig manual suggested you can use glue as well as pocket hole screws.

Apparently I was wrong. But is it significant that the panel always breaks along the glue joint? If the glue bond is stronger than wood shouldn't I be just as likely to see cracks anywhere, even in the middle of a random board?

Edge jointing has always been a pain for me. My jointer…. don't get my started on my jointer. The thing has never worked quite right. I'm sure that a lot of that is that I don't have the skills to adjust it perfectly. Trust me, I've tried. I think I even posted for help about it here once. But it's also just not that great a jointer. Replacing it is way beyond of fiscal abilities at the moment.

I've tried hand planing board edges to perfection but I can never get them quite right. Usually the issue is that the planed edge isn't at a 90 degree (flat) edge anymore. I can get a perfect 90 degree edge on the board ends with the tablesaw. But if the jointer screws up the edge of the board then the table saw will simply replicate that screwup.

Different fasteners sounds like a good idea. It can't hurt to try. One technique I've heard of is to use nails instead of screws. The idea being that nails allow for wood movement better than screws. Problem is I've never been able to pound a thin/short enough nail into anything harder than pine. I've wondered if I should pick up a small nail gun. But I don't have an air compressor and all the nail guns appear to be air powered. With the exception of the " bullet powered" models; which would be like shooting an ant with an elephant gun.


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## BinghamtonEd (Nov 30, 2011)

I agree 100% with those who said it is an issue of gluing your aprons to the top. The top needs to be free to move.

As far as getting a good glue joint, mine got noticeably better once I started using a hand plane to finish the edges. Once you have the two pieces ready to go, fold them in together like a book, and put them in a vise. Use a hand plane (I usually use a #4, unless the panel is really big, then I use #5). Take a couple swipes until you're getting a full width shaving from both boards. Then take them out and lay them flat, they should match up perfectly.

I think I saw that as the T Mac tip of the week or something a while back.

Edit : With the process, you don't need to get a perfect 90 degrees. As long as you're taking a shaving from both boards, when you fold them back, they will match up. If you're planing 1 board at a time, it gets much more difficult.


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## MikeThrockmorton (Nov 4, 2013)

Tony_S: "Don't argue with wood….it always wins."

Nice summary of woodworking technique.


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## Ripthorn (Mar 24, 2010)

I do what Ed says above, but the one thing I might add is that for this to work, you have to have minimal to no camber on the plane iron. Any camber makes the situation much worse. I look at my jointer (a 25 year old Grizzly 6") as a roughing tool. Gets all the rough work done, then just a minute or two with a hand plane and beautiful glue joints.


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## jmartel (Jul 6, 2012)

Glued joints are stronger than wood if you do the glue up properly. No needing ideal conditions. When I break apart glue joints, it's never right along the glue seam.

As far as whether you can clamp too much, that was proven true by a magazine, I believe FWW? It's only a problem with pipe clamps, though. Everything else cannot clamp enough to squeeze all glue out.


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## todd1962 (Oct 23, 2013)

I routinely get good glue joints from my jointer. Make sure your blade height and outfeed table height is set correctly. Otherwise if you have coplanar issues with your jointer then you got bigger problems.


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## Hammerthumb (Dec 28, 2012)

With all of this being said, try gluing up a panel or 2 and leave them set aside for a few months - not attached to anything. I would bet that you will see not problem with them. Your problem stems from the attachment of the top to the base as Pinto said.

Wood is very strong, and the pocket screws attachment has set opposing wood movements against each other.

Figure 8 fasteners, or an apron kerf with buttons to hold the top will solve your problem.

You have to allow for the wood movement of the top no matter how good your edge grain joinery is.


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## donwilwol (May 16, 2011)

Here is my opinion.
First if your glueing along the grain, you can't clamp to tight. 
Second, you should be pinning your aprons and not glueing. 
You can not glue end grain to long grain and have it hold. Something will fail.


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## Pezking7p (Nov 17, 2013)

Don't glue the aprons to the top. Attach them with table top fasteners that allow for movement.


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## Purrmaster (Sep 1, 2012)

Thanks for the replies. Very helpful.

I've had good luck with end grain to long grain joints. I wasn't aware that was a no no. End grain to end grain joints are a different story.


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## BinghamtonEd (Nov 30, 2011)

The only time I've used end-grain to long grain is when edging a plywood panel with hardwood, when it's going to be painted (else I'd miter it), and the hardwood trim is 1" thick or less. Even then it's just out of laziness. The strength comes from the long-grain to plywood glue joint, and the thin edging doesn't expand/contract enough to cause the paint to crack.


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## dbray45 (Oct 19, 2010)

This guy does a nice job on breadboard ends - may want to take a look:

http://www.inthewoodshop.com/furniture/BreadboardEnds.html

Should solve a bunch of your problems.


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## Purrmaster (Sep 1, 2012)

Thanks for the link. I"m not sure I understand why he's cutting tenons out of the tongue portion at the end of the table top. Why not just leave it whole?

I don't have those planes. I can make the tongue portion with a rabbeting bit on my router. Not sure how I'd do the groove on the piece that fits on the end. Don't have a dado blade in my table saw. The last time I tried to route a groove inside a piece on the router table with a straight router bit it annihilated the piece and came close to killing the bit. I think I need to get some slot cutters or something…


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## wseand (Jan 27, 2010)

From what I know about Bread Board ends are, they are used in wider tables to keep them from cupping and warping. You don't want to cut that deep of a mortise all the way across the end because it can lose stability.

From what I can tell of your problem, the Bread Board ends won't solve your problem. You need to get your squaring and glue up procedures down better.

WOODWORKINGONLINE Has some great podcasts teaching you how to square wood, and many other techniques. It is where I learned a lot of good stuff..

Squaring Wood

Good luck 
BILL


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## dbray45 (Oct 19, 2010)

Here is the thing about woodworking - 300+ ways to do something, 10 different ways to do it so it doesn't come back - unless you want it to. Look for different ways of doing things, then come up with what works for you.

No one way is perfect - just like wood, every stick is different. The whole thing is a learning process and is always changing.

Just as a note, I found that if you get the MC (moisture Count) below 6% (I try to get it below 5%), the wood moves much less and is far more stable. The wood I use as a rule is air dried versus the box stores that kiln dry at higher temperature - much of it comes from over seas and this is required to bring it into the country, kills the bugs. That does not mean that it is really dry - usually 8% - 15%. This kiln dried stuff can be very brittle.


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## waho6o9 (May 6, 2011)

After using the joiner I hand plane a 90 degree edge with

an edge trim hand plane. It was a major epiphany and I thank

LumberJocks for the knowledge.


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## a1Jim (Aug 9, 2008)

I'm 100% sure your problem has to do with wood movement as others have already said. There are web sites that give these quick build ideas making tables just using pocket screws for all of there joinery ,but it's clear that the people who design these type of projects know nothing about wood movement, Here's a link on how to work around wood movement when building tables.

https://www.finewoodworking.com/media/TabletopsFlat.pdf


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## waho6o9 (May 6, 2011)

Got it a1Jim many thanks.

1) Cleats

2) Aprons

3) Breadboards

Compliments of Fine Woodworking and Christian Becksvoort


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## TheFridge (May 1, 2014)

I've heard this mentioned over and over,here and in the past and with all due respect to those who claim it's possible to 'squeeze all the glue out' or 'squeeze too much glue out' by over tightening….it's not. It's a woodworking fallacy.
But, with that said, if all of your material is both sound and stable, as well as being prepped as it should be, using proper mill-work techniques…..there should be absolutely no reason to apply anymore pressure than you can with a firm twist with your bare hand regardless of the size of the panel.

Tony_S

Look at this, glue joint strength test

http://woodgears.ca/joint_strength/glue_methods.html


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## Tony_S (Dec 16, 2009)

Hey Fridge.

All I can give you is real life information, gained from real life experience….and a whole lot of gluing experience..

Tens of thousands of hardwood tread panels of all shapes sizes and descriptions….miles and miles…and miles of curved railing and curved stair stringers of all sizes and descriptions. Probably in the neighborhood(rough guess over 23-24 years) of 40 to 50 thousand (yes thousand) gallons of PVA adhesives of varying brand names, viscosity's, solids content, set times, etc. Hours and hours of listening to manufacturer sales reps blathering on about how much better their glue is than the other guys.
A thousand clamps in the shop of all descriptions, including pneumatic clamp carriers.

I'll give you this….I believe it is possible to over tighten clamps to the degree where enough pressure is exerted that excess squeeze out may effect manufacturers p.s.i. bond spec's, but even so, it's very minimal and still quite a bit higher than the point the wood(any wood) will fail vs. the glue line failing.

I'm not trying to blow smoke up yer arse Fridge(or anyone else). I'm just giving you my real life experience. I trust it more than a guy with a glue bottle and a bathroom scale.

IMO, If a PVA glue joint fails….it has to do with something other than excessive clamp pressure.

But, as I said before, for most common applications you shouldn't need excessive pressure either, providing the material has been prepared properly.


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