cracked table top,what went wrong?

[ken masoumi]

I thought the pine was dry enough so the wood movement would have been minimal , I glued the jointed edges ,also the end grain was also glued to the two end pieces using tung and groove.
My question is how should I have put the top together allowing for expansion/contraction of the wood?
Thank you for your help.
Ken.
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[Jerry Wright]

Tongue and groove end joint can not be glued, except in the very middle. The top has contracted and has been trapped by the ends. Search trestle tables and look at the end treatments.

[joe milana]

Yep, that design will fail almost every time. Google or search this forum for "breadboard ends. There are several ways to do them, but essentially they are attached to allow for seasonal movement of the wood. Also, you might consider running the grain lengthwise to minimize movement. Still a nice table. Consider it "character" and enjoy it.

[Jerry Miner]

how should I have put the top together allowing for expansion/contraction of the wood?

Breadboard end. This is a classic error. You have created a cross-grain situation, with wood grain running in opposing directions. The piece at the end, glued tight to the rest of the table does not allow the other pieces to expand/contract, so, instead, it cracked. (wood doesn't move much end-to end, but does move side-to-side. It's the differential that can cause problems)

Wood is never "dry enough" to eliminate wood movement. It always absorbs and releases moisture from the air in response to changes in humidity. As it absorbs and releases moisture, it changes size. This characteristic is one of the most important things woodworkers need to be aware of and provide for in the design and construction of wood projects.
A traditional breadboard end is not glued solid--it is attached with pegs (typically underneath where they are not seen) driven into slotted holes in a tenon on the end of the main top. If you Google "breadboard end" you will find examples of what I'm talking about.

Another option is to leave off the cross-grain end altogether. Lots of tables are made this way.

[Rick Fisher]

Do the tongue and groove joint, but dry fit it .. Use three screws in oblong holes and basically squeeze the breadboard end on..

[Danny Hamsley]

You can also use a sliding dovetail, and glue only the front about 2" along the breadboard edge. This is a breadboard end on a chest top that forms a lip for the chest top, but the physics are exactly the same as a breadboard on the edge of a tabletop.





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[Jeff Bartley]

Ken,
As others have stated, research 'bread board ends'. You can save the table by cutting the current bread board ends off and then properly attaching new ones. Cut beyond the tongue and then re-cut the tongue on the top, you'll have to make new ends unless you can live with a shorter top.

[ken masoumi]

Tongue and groove end joint can not be glued, except in the very middle. The top has contracted and has been trapped by the ends. .


You can also use a sliding dovetail, and glue only the front about 2" along the breadboard edge. .





249654
I searched breadboard joinery,most mentioned similar methods using pegs,dowels,etc.but if I wanted to glue it partially,would it be near the middle as Jerry says in his post or the 2" near the ends of the board?
Does it make a difference where to glue if I use tongue or groove or sliding dovetail? I really like the sliding dovetail idea.

[Kent A Bathurst]

Glue in the center...2" - 3".

Then, pegs through the breadboard ends, with elongated holes in the tops' tenons for the pegs not in the center.

Example - breadboard end, drawbored pegs through tenons, one of the elongated holes in the tenon. 43" x 84" table top. The two pegs in the center of the photo are through round holes - that is the center tenon which is glued.


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[Jeff Bartley]

Ken,
The underlying knowledge here that you may be missing is the way in which wood moves as humidity changes. An understanding of that and you'll see the light go off over your head!
Grab a piece of wood, look at the grain, wood moves across (or perpendicular to) the grain. Along the grain wood doesn't move much at all. When orienting two pieces in a cross grain (i.e. perpendicular) fashion you must allow the cross grain wood room to expand and contract. I hope this makes the physics at work here a little clearer....understanding this is crucial to designing anything built with wood!
When only the center of a bread board end is glued it directs the movement to each side......sure you could glue one edge, but then all the movement will be directed to the opposite side. Putting numbers to this: let's say the expansion is 1/8".....glue the center and you'll see 1/16" movement at each end. Glue one end and you'll see 1/8" movement at the other. I hope this helps, does it make sense now?

[Rick Moyer]

I searched breadboard joinery,most mentioned similar methods using pegs,dowels,etc.but if I wanted to glue it partially,would it be near the middle as Jerry says in his post or the 2" near the ends of the board?
Does it make a difference where to glue if I use tongue or groove or sliding dovetail? I really like the sliding dovetail idea.

Don't glue BOTH ends, only one end. Or in the middle. But I would use the method Kent outlines (even though I haven't done one yet).

[Lee Schierer]

In addition to the suggestions on construction, you can limit seasonal wood movement problems by putting equal layer of finish on all sides of a finished piece. You should finish not just the top , but the under side as well. This seals up the wood and slows the moisture gain and loss considerably, which will reduce the range of movement.

[ken masoumi]

Ken,
An understanding of that and you'll see the light go off over your head!
wood moves across (or perpendicular to) the grain. Along the grain wood doesn't move much at all. When orienting two pieces in a cross grain (i.e. perpendicular) , does it make sense now?
Jeff I knew the theory behind it but wrongly said to myself:'naahh,don't fuss over it,just glue the thing it'll be alright" now I realize it is a basic principle in woodworking,ignoring it is just pure stupidity on my part..
I will(as you recommended) cut the end pieces and redo it properly.

Kent, thank you for taking the time to post those pics,it helped to actually see the length a real woodworker has to go to deal with wood movement and here I was ignoring it.


equal layer of finish on all sides of a finished piece. You should finish not just the top , but the under side as well..
Lee,I did not put equal amount on the underside but sealed it with one coat of shellac,oppose to 3 coats on the top,now I know,thank you.
thank you all for pointing out my rookie mistakes,for me it is the only way in woodworking,trail & error,then ask why,without knowing exactly why,I was bound to repeat it.

[Frank Drew]

Does it make a difference where to glue if I use [a] sliding dovetail? I really like the sliding dovetail idea.

Ken,

Since as it slides the tail will drag glue with it, you should only glue a sliding dovetail at one end, either the last portion of the tail to enter the socket, or the last portion of the socket to receive the tail. Otherwise you'll have glue along too much of the joint leading to the cross-grain issues we're discussing. Thus no glue in the middle, either.

[Kent A Bathurst]

Kent, thank you for taking the time to post those pics,it helped to actually see the length a real woodworker has to go to deal with wood movement and here I was ignoring it.


No problem.

Thanks to Rick for picking up my fumble - it does not have to be in the center, of course....it can be on one end, forcing the expansion/contraction to all go in the other direction.

You cannot stop the wood movement. Ain't gonna happen. No matter what you try. So - you simply have to deal with it. There are certainly simpler methods than what I showed - but I was going for a specific design feature, and that means it is what it is. And - in all honesty - it really is not all that much more than what you did - you did most of the basic joinery functions, just needed to carry them a bit further, that's all.

Me - I have always been a bit nervous about sliding dovetails, for example. Dunno why - not like landing on Mars or anything, so mebbe I should simply tee it up one time, eh?

[Jeff Bartley]

Sliding dovetails are a great joint, but they're fussy.....I use a thin shim on both parts of the joint to make it a tapered sliding dovetail and then leave the glue out and simply put a peg in the center....this forces the movement of the panel (or table top) to each end.

[Gordon Eyre]

You could have built the top without the breadboard ends and then mounted it with a bracket or elongated screw holes to allow for movement.

http://www.pbase.com/greyflash/image/145169794/original.jpg

[Danny Hamsley]

The sliding dovetails can be fussy. However, they are way cool. Go ahead, Kent, take the plunge! Here is a curly cherry blanket chest with breadboard ends that utilize the sliding dovetail. The breadboard end forms the lip of the chest on the ends, and you glue a piece on the front for the front lip.

However you decide to go, you have to allow the panel to move in the breadboard end just a bit. As has been pointed out in a prior post, you cannot glue a sliding dovetail in the middle because the breadboard (tail) has to slide on the end of the top (pin), and that would smear the glue too much in the joint. So, you glue about two inches on the "show" end. In this case, the "show" end is at the front miter joint. However, the wider the top, the more "fussy" a sliding dovetail can be. Do not cut the joint until you are ready to complete the breadboard.

[Ira Matheny]

I recently discovered the attached table that show wood movement based upon moisture content. I found it interesting and rather enlightening.
http://garagewoodworks.com/moisture.php