Common Wood Defects

1. Common Wood Defects Woodworking Technology Mr. Johanson

2. What Are Wood Defects • The lack of something necessary or desirable for completion or perfection; a deficiency: a visual defect. • An imperfection that causes inadequacy or failure; a shortcoming. See synonyms at blemish.

3. What Are Common Wood Defects • Lets explore a few you might encounter in class

4. Bow A bow is a defect in a board that bends along the grain lines. If the board were laid across a flat surface both ends would be in the air. There is no warp across the grain. This can be caused by uneven air circulation during as the wood dries. Any bowing causes internal stresses that will make the board difficult to cut. Ripping a board that is bowed can be dangerous. Crosscutting should be done with the bow facing upwards.

5. Checking A check is a term used to describe a crack that runs through a board, usually running lengthwise. It is usually caused when lumber dries out too quickly. Adding a UV protective stain can help protect decking and rails. Checking often affects pressure treated framing materials as they are usually sold very green and are put under a lot of stress as they dry out in the sun. Thicker members like 6x6 posts tend to dry out unevenly and are especially susceptible to extreme checking.

6. Crook A crook is a defect found in a board that is bent end to end in the direction of the tall ends of a board as it continues down the length of the board. It can occur from uneven drying or if the trees pith (soft core at the center of the tree) is at the edge of the board. You may be able to rip the board to recover a narrower straight board, or make multiple passes through a jointer.

7. Cupping Cupping occurs when the board bends edge to edge across the face of a board and where the ends of the boards will look like the letter U. It is common in boards that are cut close to the pith. Cupped boards can be ripped into smaller boards and planed. Trying to force it flat can cause cracking.

8. Split A check is a term used to describe a crack that runs through a board, usually running lengthwise. It is usually caused when lumber dries out too quickly. Adding a UV protective stain can help protect decking and rails. Checking often affects pressure treated framing materials as they are usually sold very green and are put under a lot of stress as they dry out in the sun. Thicker members like 6x6 posts tend to dry out unevenly and are especially susceptible to extreme checking.

9. Twist Twisting is a general term for a board that that bends in any variety of directions and cannot maintain a straight line. Sometimes one corner doesn’t line up with the others. It usually occurs when the wood grain pattern is not parallel to the edge.

10. Wane The presence of bark or the absence of wood on the corners of a board is called wane. This defect will only be found in lower grade lumber. You may be able to turn the board over to conceal this kind of defect in some applications.

11. Conclusion • Wood is a natural material and is subject to natural imperfections. • Some defects can be machined out some defects cannot. • Choose your lumber carefully and try not to select material with as few defects as possible.