LUMBER DEFECTS

L

umber defects may reduce a board’s strength or workability or mar its appearance. Or, in the hands of a cre­ative woodworker, some defects may in fact become visual assets, transforming an ordinary piece into a work of art.

Most defects, however, are undimin­ished trouble. Although some may result from damage to the standing tree or the lumber cut from it, the greatest number of defects are produced by irregular dry­ing of the wood.

The chart below illustrates some of the most common defects and details the way in which most can be correct­ed; with diligent use of the band saw, even the most seriously cupped boards can be salvaged (page 21).

DEFECTS IN WOOD

 

REMEDIES

Tight knots can be cut out or used, as appearance dictates; dead or loose knots must be removed before working with stock.

Do not use stock if a quality finish is required, as gum will bleed through most finishes.

 

CHARACTERISTICS

Appears as a whorl encircled by sound tissue. Formed as girth of tree increases, gradually enveloping branch. Live branches integrate with surrounding wood, resulting in tight knots; dead stubs cannot integrate with surrounding tissue, forming dead or loose knots.

An accumulation on the surface of the board or in pockets within the board. Usually develops when a tree has suf­fered an injury, exposure to fire, or insect attack.

 

TYPE

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Lengthwise ruptures or separations in the wood, usually caused by rapid drying. May compromise strength and appearance of board.

 

Can be cut off.

 

Flatten bowed boards on the jointer, or cut into shorter pieces, then use the jointer.

Cupped boards can be salvaged on the band saw (page 21) or flattened on the jointer.

 

An end-to-end curve along the face, usually caused by improper storage of lumber. Introduces internal stresses in the wood that make it difficult to cut.

An edge-to-edge curve across the face. Common in tangentially cut stock, or boards cut close to the pith, if one face of a board has less contact with the air than the other.

 

Board can be salvaged by jointing and ripping waste from the edges. Crooked boards remain unstable, and may not stain or finish well.

Board can be flattened on jointer, or cut into shorter boards.

 

End-to-end curve along the edge, caused by incorrect seasoning or cutting the board close to the pith of a tree. Weakens the wood, making it unsuitable for weight­bearing applications.

Uneven or irregular warping when one corner is not aligned with the others. Results from uneven drying or a cross-grain pattern that is not parallel to the edge.

 

Crook

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Board can be used, but split may mar the appearance of the wood, becoming more noticeable when stain is applied.

 

Similar to checks, appearing as separations along the growth rings. Also known as ring check or ring shank. – Results from improper drying of wood or felling damage.

 

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