Fundamentals Of Wood Flashcards
Wood microstructure
Cellular composition of wood consisting mainly of hollow tubes oriented along the length of the members resembling a bundle of straws glued together.
Wood growth patternn
The properties of wood products relate directly to the natural growth of wood.
• Wood generally grows in a circular pattern;
• Seasonal change - different rates throughout each year
• Climatic change - different rates from year to year
• These different rates of growth produce the ring pattern found in all wood (more distinctive in softwoods).
First year growth
First ring
Rainy season growth
Thick ring
Dry season growth
thin rings
Spring yearly summer growth
Light coloured rings
Late summer/fall growth
Thin dark rings
Tree layers
Outer bark, inner bark, cambium, wood
Heartwood
Inner core of wood, ceases to transmit moisture and hardens
Sapwood
Outer layers of wood, continues to transmit moisture
Hygroscopic
Ability to absorb moisture
Anisotropic
Tends to Change dimensions at different rates in different directions
When does shrinkage begin?
When moisture content falls below the finer saturation point
Softwood saturation level
25 to 30%
Hardwood saturation level
30 to 35%
Seasoned wood MC content
19% or less
Ways to season wood
Air drying, kiln drying
Air drying
Reduces mc to 15 to 20%, takes 8 to 16 months
Kiln drying
6-8 weeks
Flat sawn (plain sawn)
Flat sawing of a large diameter log, in 2 directions yields several pice’s of dimension lumber and Timbers.
Small diameter, the sawing may be along one direction only, giving primarily dimension lumber.
Certain cuts have less stability
Quarter sawn
All cuts have good stability
Primarily used for flooring
X symbol
Surfaced or rough framing lumber /ontinuous member
/ Symbol
Surfaced or rough framing lumber, interrupted member
))) symbol
Worked or finish lumber
