I was in a local hardwood supplier who does millwork and saw an absolutely beautiful walnut table top that had been put together for a client. My question is about the joinery, which to me was not done properly.
The table top was made up of 8/4 walnut which was about 12 inches wide. The width of the table was probably 5 feet (being made up of 5 separate planks). The length was about 10 feet long, with the “interior” walnut being about 8 feet long (grain running lengthwise). At each end they had biscuit joined a piece that was 1 foot wide by 5 feet long across the table, much like a bread board end. But the joint was entirely biscuited and glued.
My question is about this joinery. I’d think that the table would rip apart, eventually, as the middle of the table expanded and contracted. Even if the walnut were quarter sawn, my rule of thumb is expansion of about 1/8th of an inch per foot, so the table could theoretically expand/contract over half an inch.
The reply I got from the folks who had made it was that finished properly the table was just fine. Who’s right here?
Replies
John,
The top will crack. The glue joint between the end caps and the long boards cannot survive the inevitable movement that will occur with changes in humidity. There is no strength between the end grain of the long boards and the long grain of the cap piece. The biscuits will add no strength to the joint. There is no way to contain or constrain the wood movement. No finish, no method of encapsulation that is suitable for furniture will work. It is inevitable and inexorable.
This is classic breadboard design territory. The end cap of a breadboard is secured only for a short part of the middle of the joint so that the rest of the joint can move. And the cap and longboards are joined by some form of tongue and groove arrangement.
R
Edited 11/7/2002 6:50:15 PM ET by Rich Rose
Rich,
Thanks for confirming my suspicions. This is a very expensive conference table that will cause no ends of grief to the end customer. I couldn't believe my eyes that it was done this way.
My guess is someone will have to saw off the two end pieces and redo the table, eventually. Quite a bummer. But not my problem, since I didn't do the table top.
And thanks for the quick reply.
John,
Any idea what they finished it with? Someone seems convinced that he has "sealed up" the wood. (NOT)
From their reply it seems that they were aware that it was necessary to cope with humidity changes.
I should modify what I said slightly. I said that the biscuits will not add any strength to the joint. The joint (end grain to long grain) is stronger with them than without them as they do create a little long grain gluing surface. But they will do nothing to stop the wood movement.
Rich
The top was unfinished when I saw it and whoever commissioned them to build it was responsible for finishing it.
I clearly agree with your comments and am still flabbergasted that it was built this way. The conference table was probably a $10,000 commission piece. (This is, after all, Los Angeles.) Absolutely beautiful, and a disaster waiting to happen.
John,
Ah. So those fools are saying that WHEN finished right, the top will have no problems!
I wouldn't be surprised if the person responsible for finishing it rejects it. Unless he also specified the details of the joinery. But, Hell. Someone on the design end or building end should know better.
R
Yep. It'll be interesting to hear how this one turned out. My guess is that the fabrication was done to someone else's specs. But who knows?
Rich, I've got something else for your opinion, also dealing with joinery and wood movement.
I build high end chess boards pretty much as a hobby. I still work full time and do woodworking as a therapeutic hobby. You can see examples of my work at http://www.legendproduct.com. Search for chess boards and then look for my name (John Hardy).
My boards are solid wood, and I use solid walnut for the outside border. All joints are splined, including the outside pieces (border to board as well as the 45 degree miter joints). I've never had one rip apart.
I suspect this is because the size is reasonably small (the inside dimension is well less than 2 feet).
Do you see any design problems with this sort of joinery?
I'm a purist and making boards out of MDF with hardwood veneer (shop made) on top and bottom sort of turns me off.
And how do you like the boards?
John
John,
Very nice work. If you've never had a board fail, that pretty much confirms that the joinery is sound. I would assume that there are stresses occuring in all that glue area and that the wood is moving. But I guess that there is not enough uncompensated movement to cause any problems.
For a treat, take a look at "Hitting the smalltime..." in Woodworkers Cafe.
R
Rich,
I'm new to the FW forum and am unfamiliar with Woodworkers Cafe. How do I access it? Thanks.
John,
There are several (arbitrary) categories of messages here. I'm using Internet Explorer on a Mac and on a PC. The message categories show up as a scrolling list on the left side of my browser windows. The categories include "Tools for Woodworking," "General Discussion," "Finishing," "Joinery," "Plans," "Woodworkers Cafe," "The Gallery," and others.
The display with the scrolling list shows up after you click the "Messages" button after you log on to the Forum.
Can you see that scrolling list of categories and the messages within them on your browser?
Rich
Edited 11/8/2002 1:02:54 PM ET by Rich Rose
Thanks. Got it, and the work is exceptional.
I agree with all who say this was not the right way to make this joint. Nevertheless it may survive. Wood only responds to changes in humidity. If the conference table survives aclimating to it's new home in the first place it may be OK indefinitely in the relatively stable artificial environment of the typically year-round air conditioned and humidity controlled corporate office in LA. But I wouldn't take that chance.John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
How long is never? I am wonder because I built a solid wood board when I was in Junior High and it looked fine and stayed together for at least seven years but it has failed. I am sure the failure is also the result of moving from relativley humid California to very dry Colorado.
Just wondering how long your boards have been around because in part, I am always wonder about projects that I have completed.
Lomax
Michael,
My boards are not that "old". The first one is about 4+ years old but there is absolutely no sign of any problem. I think Rich is correct in what he said.
Rich, Is there ANY benefit to WAXING the portion of the T & G groove that is not glued at the center so as to FACILITATE seasonal movement of the wood? I wonder as I enter into my second pine table with a breadboard end (the first one without wax!) Rich Collins
Rich,
I don't know. I've never heard of the joint being lubricated, or really needing it. I suppose if the joint were so tight that it couldn't move it would crack. But I've never seen that happen. And I don't know how such a tight joint could be put together, anyway.
On the other hand, I don't see how applying wax could harm the situation. Maybe you could let us know what happens?
R
Thanks for the advice. I just may try wax on my next table. I have to admit that the joint in question on my first pine table is not so terribly tight. I call it "country rustic by default!" Rich Collins
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