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Questions and Answers
What is the result of the surface of the wood lifting in small flakes or layers?
What is the result of the surface of the wood lifting in small flakes or layers?
What can cause the grain of the wood to run obliquely to the longitudinal axis?
What can cause the grain of the wood to run obliquely to the longitudinal axis?
What is the impact on bending strength when the grain slope is 1 in 25?
What is the impact on bending strength when the grain slope is 1 in 25?
What happens when wood dries too quickly?
What happens when wood dries too quickly?
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What is the result of case hardening on the wood?
What is the result of case hardening on the wood?
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How can case hardening be cured?
How can case hardening be cured?
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What can be caused by incorrect seasoning of the wood?
What can be caused by incorrect seasoning of the wood?
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Why is diagonal grain direction not important in most cases?
Why is diagonal grain direction not important in most cases?
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What is the primary reason for distortion, splitting, and other forms of defects in wood?
What is the primary reason for distortion, splitting, and other forms of defects in wood?
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What is the purpose of weighting down during wood seasoning?
What is the purpose of weighting down during wood seasoning?
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What type of defect occurs when the plank hollows across the width and forms a rounding on the underface?
What type of defect occurs when the plank hollows across the width and forms a rounding on the underface?
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What is the term for the distortion that occurs when the wood remains flat but bends edgewise on its own plane?
What is the term for the distortion that occurs when the wood remains flat but bends edgewise on its own plane?
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What is the primary cause of end splitting in wood?
What is the primary cause of end splitting in wood?
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What is the term for the small splits that occur on the wood surface along the grain due to too rapid drying in hot sun?
What is the term for the small splits that occur on the wood surface along the grain due to too rapid drying in hot sun?
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What is the term for the distortion that occurs when the plank twists on its longitudinal axis, resulting in straight long edges but curved diagonals?
What is the term for the distortion that occurs when the plank twists on its longitudinal axis, resulting in straight long edges but curved diagonals?
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What is the term for the synonymous terms for distortion in one or more directions?
What is the term for the synonymous terms for distortion in one or more directions?
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What is the primary purpose of drying wood?
What is the primary purpose of drying wood?
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What is the method of drying wood that involves air circulation around every piece of lumber?
What is the method of drying wood that involves air circulation around every piece of lumber?
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What is the name of the structure used for kiln drying?
What is the name of the structure used for kiln drying?
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What is the term for the tendency of wood to shrink and swell?
What is the term for the tendency of wood to shrink and swell?
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What is the unit of measurement for lumber that is 12 inches wide and 1 inch thick and 1 foot long?
What is the unit of measurement for lumber that is 12 inches wide and 1 inch thick and 1 foot long?
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What is the main axis of the tree in relation to the wood grain structure?
What is the main axis of the tree in relation to the wood grain structure?
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What is the term for the process of scientifically heating wood to dry it?
What is the term for the process of scientifically heating wood to dry it?
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What is the primary benefit of kiln drying over natural drying?
What is the primary benefit of kiln drying over natural drying?
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Study Notes
Wood Defects
- Flaking: wood surface lifts in small flakes or layers, preventing a smooth surface, due to structural weakness or incorrect seasoning.
- Diagonal grain: grain runs obliquely to the longitudinal axis, making surfacing more difficult, and reducing impact strength and bending strength.
Case Hardening
- Occurs when wood dries too quickly, causing dry outer layers to be in tension and moist interior in compression.
- Cuts that close ahead of the saw are often due to case hardening.
- Can be cured by steaming and redrying.
Important Properties of Timber
- Strength and related properties of toughness, rigidity, and hardness.
- Workability.
- Drying properties and related tendency to shrink and swell.
- Bending qualities.
- Grain structure and figure pattern.
- Gluing properties.
- Finishing.
- Resistance to weathering and insect damage.
Methods of Drying Wood
- Natural drying (air-drying or sundrying): lumber is strip-piled at a slope on a solid foundation.
- Kiln drying: done in a dry kiln using steam pipes.
- Water seasoning.
Unit of Measurement
- Board foot: a piece of lumber 12 inches wide and 1 inch thick and 1 foot long.
Types of Wood Grain Structure
- Straight grain: fibers running in the same direction as the main axis of the tree.
- Inter-locked grain: grains in successive layers and in opposite directions.
Artificial Defects
- Caused by incorrect seasoning, creating internal strains and stresses.
- Normally, the natural elasticity of a healthy wood structure distributes these stresses evenly.
- Weighting down during seasoning helps to reduce distortion.
Types of Distortion
- Cupping or rounding: the plank hollows across the width, forming a rounding on the underface, often due to incorrect piling.
- Bowing: the plank is curved like a bow throughout its length.
- Springing: the wood remains flat but bends edgewise on its own plane.
- Twisting: the plank twists on its longitudinal axis with the result that the long edges are straight, but the diagonals are curved.
- Warping, casting: synonymous terms for distortion in one or more directions.
- End splitting: the butt end of the plank splits open, usually caused by too rapid drying.
- Sun checking: small splits along the grain caused by too rapid drying in hot sun.
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