Articles Wood Movement

I learned the hard way. (Do we always have to learn that way?) One of the first projects I made, was a chest of drawers. I was making it with the remains of one I found at the dump. The wood was maple and looked beautiful, but I had a lot to learn. The crack that eventually formed goes right up the middle of one side, right across the top, and down the other side. The whole thing literally split in two. The good news for me is, I learned right away, on that first project, and the wood was free.

Without going into the details of why wood moves in the directions it does, I'd like to just present the facts and some methods to account for wood movement in various projects. This of course will not be a complete list, and if you would like to send me your ideas, I can add them to this article and let it grow. I am still learning.

• Wood expands and contracts across the grain significantly more than lengthwise with the grain.

• When joining boards with the grain running at 90° angles to each other, never glue rigidly all the way across the grain. As the wood expands or contracts it will weaken or break the bond or if the glue holds, it could split the wood. Wood of the same species can always be rigidly joined when their grain runs in the same direction.

• When joining wood across the grain, affix the wood rigidly in one spot (either end or in the middle) and allow the rest of the board to move. To attach the two together, use a mechanical fastener, such as a screw, with an elongated hole, which will allow the wood underneath to move. (See fig. 1 )
  
  
• For a dresser or desktop, you would rigidly affix at the front to maintain the front of the piece's dimensions allowing the wood to grow toward the back, where the growth or shrink will not be seen. In the example above, the boards would run left to right across the top.

• Breadboard ends use a similar method to attach a finish piece of wood covering the end grain of the breadboard. In this case you attach the end board rigidly in the center, since both sides are seen and the movement is cut in half. The two edges are affixed with wooden pegs, with elongated holes in the edge of the breadboard. (See fig. 2 ). Note the tenon should not be as wide as the mortise to all for it to grow a little.
  
• Remember than boards will grow and shrink with the seasons and allow for that growth when making doors and drawers. For doors of any size, make the door a frame and panel door. The narrow width of the frames will keep the door from changing size significantly.

• When making doors with panel inside a frame, remember to either let it float, with grooves deep enough for the wood to grow, and the panel wide enough such that when it shrinks it won't leave a gap at the edges. The panels should be fixed in the center to allow the wood movement to be split 50% to each side.

• When making up a large panel such as you would use on the back of a hutch or bookcase. (If you intend to use solid wood) a panel made up of shiplapped boards allows each board to move independent of all the others. Typically otherwise on such a wide panel, the frame would not be able to contain the panel's movement.

• When a wide board moves, it tends to cup, unless it is quartersawn. Quartersawn wood has grain that when viewed from the end, are in relatively straight lines across the board in the narrow dimension. Typically wood is not cut this way, since there is more waste this way. However some boards will still come out this way when the log is cut.

• Unless you have the great fortune to be using a lot of quartersawn wood, when gluing up boards to make a wide board, resist the temptation to do it with a few wide boards and use many narrow boards. When joining the boards, every other one should be flipped such that the bark side is turned opposite of the ones next to it. This tends to cancel out the tendency to cup and keeps the glued up board flat.

• When finishing wood, you should finish both sides in the same manner and to the same degree. This prevents one side of the board from absorbing more moisture than the other absorbs.

• If you make anything out of wood, you should remember that what you are making is going to move. Even if you seal it tight with paint or varnish, it will expand and contract somewhat. But the less you seal it, the more it will move. Some woods move a great deal with changes in humidity, others less so. Then, too, how the wood was cut from the log will determine how much the wood moves.

• Planning for wood movement. This is the secret to success. If you plan for some movement, in the proper direction, then even though it doesn't work for you, it won't work against you. When a wide board is used and fastened along its grain, plan for the wood to be moving. When multiple boards are used for instance in the back of a hutch, a shiplap arrangement should be used, so that each board has room to grow and shrink. Or boards can be fastened in the middle and allow them to grow out in both directions. Sufficient gaps should be left to allow room for movement. If a dresser or tabletop is to be securely fastened, pick a side to be fixed (usually the front) and screw it securely. Then each of the holes as you move to the back, should be made elongated, and the screws attached with washers to allow the top to move backward and forward.

• On a deck, remember that those pressure treated boards will shrink, significantly! So when leaving a gap, keep it small (or leave none) and allow for that shrink.