Failure of glue joints at the ends of tables

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Forum topic by Purrmaster posted 09-09-2014 04:35 AM 4034 views 1 time favorited 31 replies Add to Favorites Watch
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915 posts in 2357 days

09-09-2014 04:35 AM

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.


31 replies so far

View Aj2's profile


1983 posts in 2062 days

#1 posted 09-09-2014 04:49 AM

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

-- Aj

View wseand's profile


2796 posts in 3306 days

#2 posted 09-09-2014 04:51 AM

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

View longgone's profile


5688 posts in 3573 days

#3 posted 09-09-2014 05:04 AM

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.

View RogerInColorado's profile


321 posts in 2219 days

#4 posted 09-09-2014 05:13 AM

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.

View pintodeluxe's profile


5855 posts in 3078 days

#5 posted 09-09-2014 05:16 AM

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.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View Purrmaster's profile


915 posts in 2357 days

#6 posted 09-09-2014 07:25 AM

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?

View exelectrician's profile


2339 posts in 2692 days

#7 posted 09-09-2014 07:33 AM

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.

-- Love thy neighbour as thyself

View jinkyjock's profile


488 posts in 1839 days

#8 posted 09-09-2014 09:54 AM

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).

View Tony_S's profile


953 posts in 3347 days

#9 posted 09-09-2014 09:56 AM

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.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View JayG46's profile


139 posts in 2123 days

#10 posted 09-09-2014 10:39 AM

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.

-- Jay Gargiulo, Naples, FL "Once you understand the way broadly, you can see it in all things."- Miyamoto Musashi

View TheWoodenOyster's profile


1317 posts in 2199 days

#11 posted 09-09-2014 12:23 PM

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.

-- The Wood Is Your Oyster

View Purrmaster's profile


915 posts in 2357 days

#12 posted 09-09-2014 12:42 PM

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.

View BinghamtonEd's profile


2298 posts in 2634 days

#13 posted 09-09-2014 12:44 PM

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.

-- - The mightiest oak in the forest is just a little nut that held its ground.

View Mike Throckmorton's profile

Mike Throckmorton

124 posts in 1929 days

#14 posted 09-09-2014 01:18 PM

Tony_S: “Don’t argue with wood….it always wins.”

Nice summary of woodworking technique.

-- You are never complete, you just draw a line where done is and stop at that line.

View Ripthorn's profile


1459 posts in 3249 days

#15 posted 09-09-2014 01:50 PM

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.

-- Brian T. - Exact science is not an exact science

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