Allowing for Wood Expansion on Solid Wood Tops
George VondriskaDescription
Wood moves; there’s nothing you can do about it. Even after the tree is down, the wood has been dried, you’ve got it in your shop, and you apply finish, wood is gonna move. It’s a living, breathing thing. If you don’t allow for wood expansion, you’re going to have problems in the future. Problems being cracking, splitting, maybe even blowing a leg and rail assembly apart. Let’s not let that happen.
Do’s and Don’ts
To give solid wood pieces plenty of opportunity for wood expansion, here’s a list of things you should and shouldn’t do:
- Don’t glue a solid wood top to the rails in the base.
- Don’t screw the top in place, unless the screw holes have sufficient wiggle room to allow for wood expansion.
- Do use tabletop fasteners. They’re easy to use, and allow wood movement by sliding along a kerf in the rail as the solid wood expands and contracts.
- Don’t worry about plywood or other man-made slabs. They don’t have the seasonal movement that solid wood does.
Direction Matters
Wood only expands and contracts in one direction; perpendicular to the grain. Depending on the specie of wood you’re working with, it can move as much as ¼”, or even more. You don’t need to worry about expansion and contraction parallel to the grain.
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When you build a piece of furniture and you're gonna use a big solid wood slab, like this tabletop, you've gotta take some things into account. And Sam, the director and I were just talking about this. They've got a big kitchen table at their house where this wasn't taken into account. We'll talk about that. And things are going just a little bit south. So here's what happens. This is a 28 by 28 inch top in red oak. It's gonna seasonally expand and contract maybe as much as a 1/4 of an inch, maybe more. So, as temperature changes, as humidity levels change, this top will be forever moving. Now you can stain it, you can seal it, six surfaces. Six being two faces and all four edges. It can be completely sealed up with polyurethane, and it's still gonna expand and contract seasonally. And you've gotta allow that to happen. If you don't, the top is gonna crack or the base is gonna blow open, or something bad is gonna happen. So, a couple of things going on here. Keep in mind, the way it's sitting here is the way it's gonna go on the table, the grain is this way. Now the reason that's a big deal is, one of the ways I commonly approach this is using what are call tabletop fasteners. So, if you look at the rail here, there's a curf that was cut in there before the rail was incorporated into the table. And into that curf will go a commercially available tabletop fastener. And if you Google these, they're simply called tabletop fasteners, you're gonna find 'em. The way this works is, through that hole, I can drive a screw into the bottom of the top, and that provides pressure that holds the top firmly but not rigidly against this rail. As the top wants to expand and contract, that metal clip is able to slide back and forth. In a top of this size, what I would most likely do is put three clips in this rail. Now, when you get the clip out toward the end, make sure that it's not right up against the leg, because then if that wants to expand in that direction, it can't. So I'd hold that clip in a couple inches off the leg so it's got some wiggle room. I love using pocket holes for projects. This is not a good place to use 'em because, if I have a pocket hole and a pocket hole and a pocket hole, it's those screws are gonna firmly fix the tabletop in place, not allow it to expand and contract. Certainly what we don't wanna do is put a bead of glue on top of this thing and glue it down. Now I talked about grain direction and why that's a big deal because, seasonally, this chunk of wood is gonna expand and contract across its width. It's not gonna change its length. So we have to allow expansion this way, we don't have to worry about it this way. So the clips only go in the rail, or rails that are perpendicular to the grain direction. So the clips only go in these two rails on opposite ends. They don't have to go in the other ones. In fact, we don't want 'em in these rails, because if we clip it there, that's gonna inhibit its movement across its width. So, take those kinda things into account. Don't fight mother nature here. You can't fight her and win. So, allow this to expand and contract, tabletop fasteners are a great approach to letting that happen. And your tops and bases will remain crack-free through the life of the project.
So with the carcass of lets say a tv cabinet and your using dovetails how wood wood movement work?
Question regarding wood expansion. Example a table top that is, in your example 24x24x1, the expansion is perpendicular to the grain. Is there expansion in the vertical direction? It does not matter for a table top but other construction scenarios it could affect the thickness if it expands vertically and is in a critical location.
great video about using top clip and also about grain direction
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Milled lumber is not a living, breathing thing. In fact even long before a tree is felled a high percentage (the heartwood) is dead. Cellulose is hygroscopic - that is why it shrinks and expands. Movement with temperature change is negligible - don't even mention it. Please stop propagating these old wood-wives tales.
We have a beautiful dining table with a solid distressed top and a heavy metal base. The top seems to be made of 4 glued boards with 4 metal strips screwed across and underneath to each board and 3 threaded rods run through holes drilled in the boards and bolted on the exposed and recessed ends. So, this thing is seriously held together mechanically across the grain and has showed no signs of expansion or contraction in the 2 years we have had it. I am building another one for our sun room out of 2x8 solid oak floor joists that have been planed to about 1 3/4" thickness and was planning on mechanically connecting these boards kind of like our other table, but maybe without the threaded rods. So, my questions are will our current table explode some day like someone below said their's did and am I crazy to want to emulate our current table's design which seems to be holding up?
<strong>NB Ticket 16848 Hi, what if I created a table top out of 2x6s, secured together by pocket-hole screws + glue ("farmhouse" style coffee table). Basically I have 7 2x6s side by side, with 2 other 2x6s on each end to create a square table top. I'm noticing pretty decent gapping starting to form between the 2x6s. Is this just a nature of creating tables in this way? Any suggestions for if and when I decided to give it another shot? Thanks for the help!
I'm just getting started on a sofa coffee table and am so glad I saw this video as the plans called for pocket holes all along the perimeter. One question I have though, the plans call for a lower shelf that is not quite as deep as the lower stringers. I'm guessing I should allow for the same expansion/contraction on the lower shelf as the table top itself. Would the best way to place the kerf in the middle section of the stringers be to drill press and chisel them? I guess I could alter the plans and make the shelf the full depth but I like the look it offers being slightly smaller.
How would you incorporate this into a table with a round base, especially circular? If the shape is more of an oval or if the radius of the circle is large enough, then I would assume you just don't put the clip all the way into the kerf so that it still has a little room at the tip to move within the curve? What about when you have a tight radius at the end that would be perpendicular (or a tangent line would be perpendicular) to the grain, for instance if you have a long narrow coffee table, sofa-back table, bar top, etc.--cut a deeper kerf (if possible) to give more lateral room for movement? Also, you said not to glue or screw the top to the table base, and in another comment you advise against putting in even a single screw in the middle--how is this different from breadboard ends, where you have said in other videos to glue only the center portion (center 1/3 or so) in order to allow for expansion at the edges? Wouldn't a solid top and a top made from multiple pieces glued along the edges both expand and contract similarly? Why glue one in the center and not the other?
As someone who's repaired a lot of furniture, the Chinese furniture factories either need to know this or need to care. I've had customers who say, "We awoken in the middle of the night with what sounded like a gunshot. We came out and found this giant crack all down the top of our dining table. "You can't control wood movement, you can only account for it."