Wood Expansion

[Jerry Bittner]

In the process of making a dresser. the top is roughly 3/4 inch x 39 x 20 made up of three boaads biscuit joined on edge.

Of course in mounting the top, I'll enlarge the holding screws to allow for expansion. However, the pland call for the four corners of the top to be between the four legs in what the plans call for a tight fit.
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My concern is that if I follow the plans to the "t", the legs may prevent the board from expanding.

Is that a real concern and if so, should I allow a little space bewteen the top and the legs and if so, how much -- a 1/32 on each end?

[Jerry Bittner]

Woops, my little diagram did not hold up. What I was trying to illustrate was the top has four cutouts to accomadate the legs

[Jim Becker]

As long as you account for the same movement in any aprons/stretchers, you shouldn't have any issues...

[Jerry Bittner]

Aprons, stretchers -- sorry but me limited expereince doesn't carry me to understanding those terms. But thanks for the quick response Jim

[Jim Becker]

All the other components of your table that tie into the legs, Jerry. Aprons support the top and are usually tied into the top of the legs. Stretchers when used are farther down towards the bottom of the legs to keep them stable under stress. You need to build the whole project with wood movement in mind...

[Alan Turner]

Jerry,
As I understand the design, the solid wood table top is trapped between the 4 leg posts, which extend into or above the top. If there is no way for the tops of the legs to move with the seasons, then I would think you would have a potential problem. I wonder if the table was designed for a plywood or mdf and veneered top?

I would leave some room for movement here as I think you will likely need it.

[Jerry Bittner]

Yes, the top is trapped between the four legs. I have allowed for a little movement, about a 32 second on each end of the table top where it abuts the four legs so that gives me 1/16" of movement on each side.

Think that's enough? -- realizing that the room for expansion will depend upon humitdity and temperature. Could go more but then the gap starts to get obvious.

[Alan Turner]

To answer your question of the needed room for expansion, you need to know the type of wood, its present moisture content, and the range of EMC is will be exposed to. With this, google the "shrinkulator", plug in your values, and you will know the minimum and maximum range of motion.

[Jules Dominguez]

You need to know how much the moisture content of the wood will vary both up and down after you assemble the table, and whether the tabletop boards are radial or tangentially cut from the tree, which determines the percentage shrinkage and swell. Without knowing any of that, I'd still think that 1/16" total allowance across a 20" wide table top is unlikely to be sufficient.