Common Wood Defects

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Common Wood Defects

• Woodworking Technology
• Mr. Johanson

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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.

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What Are Common Wood Defects

• Lets explore a few you might encounter in class

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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.
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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.
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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.
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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.
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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.
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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
doesnt line up with the others. It usually
occurs when the wood grain pattern is not
parallel to the edge.
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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.
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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.