Wood Technology

Harvesting Trees There are 2 methods for harvesting trees Clear Cutting and Selective Cutting Harvesting trees is the process of cutting down trees in order to use them for products that fulfill human wants or needs Many of the products you use on a daily basis have come from trees that were harvested Some of these items include: paper, pencils, tables, chairs, buildings, etc.

Clear Cutting Clear cutting is a method of harvesting trees in which all types and sizes of trees are cut. Most environmentalists disapprove of this method.

Selective Cutting Selective Cutting is a method of harvesting trees in which only trees of a certain size and type are taken. This method is preferred over clear cutting by environmentalists.

Sawing Lumber Plain-Sawn lumber is a method of sawing lumber where the log is cut parallel to the growth rings. Plain sawing results in a greater amount of planks; however, they are more apt to warp, and tend to check or split. On a positive note, it costs less and there is less waste of the total tree.

Sawing Lumber Quarter-Sawn is a method of cutting lumber where the annual growth rings are perpendicular to the face of the board. Quarter-Sawn boards tend to be more dimensionally stable than other forms of sawn lumber, but it costs more and creates more waste of the tree. The process starts by cutting the logs into 4 sections called quarters.

Seasoning (Drying) Lumber Air-Dried Lumber is usually dried outdoors, to an equilibrium moisture content with the air it was exposed to after being sawn. Moisture content can usually be down to 10%-15% using air drying.

Seasoning (Drying) Lumber Kiln-Dried Lumber is lumber that has been dried in a building or shed where temperature, moisture, and the amount of air circulating are controlled to dry the wood. Moisture content can usually be down to 6% to 8% within 24 hours.

Stacking Wood Before the drying process, wood is stacked using stickers. A sticker is a thin wood strip that is inserted between stacks of green wood to allow air to flow through the stack to ensure proper drying.

Types of Wood Hardwood is one type of wood Hardwood is generally lumber from a deciduous tree such as maple, oak, cherry, or walnut. Deciduous trees are trees that lose their leaves annually

Types of Wood Softwood is another type of wood Softwood is generally lumber from a coniferous tree such as pine, spruce, fir or cedar. Coniferous means cone bearing In other words a tree that has cones

Parts & Growth Characteristics Annual Growth Rings The layer of growth that a tree puts on in one year. The annual growth rings can be seen in the end- grain of lumber.

Earlywood Springwood- The lighter/wider part of the tree’s rings to form after winter hibernation. Often characterized by larger cells and a lower density.

Latewood Summerwood- The portion of a tree’s rings that forms after the earlywood. Often characterized by smaller cells and a higher density.

Bark/Cambium BARK The outermost, protective layer (From weather, insects, and disease), of a tree composed of having dead wood and other elements. CAMBIUM The inner, actively growing, layer of a tree The cambium is one cell thick and resides between the sapwood and the phloem. It repeatedly reproduces itself to form new wood and causes the tree to live and grow

Heartwood The dead inner core of a tree (heart). Usually much harder and darker than the newer wood.

Sapwood The newer wood in a tree that lies between the bark and the Heartwood. Sapwood is usually lighter in color and becomes heartwood as the tree grows.

Pith/Wood Rays/Lignin The soft core in the center of the tree trunk Wood Rays A worm like figure caused by the strands of cells which extend across the grain in quarter-sawn lumber. Carries water and nutrients outwards from the center of the tree. Lignin An adhesive substance (glue) that holds the wood cells together.

Parts of a Tree Bark Cambium Sapwood Heartwood Pith Wood Rays

Lumber Defects Defects Knot – branch or limb that has been exposed as the log is cut into lumber Check – lengthwise separation of the board Small crack or split Split – lengthwise break or split Decay – rotting wood Stain – discoloration Wane – lack of wood on the face of the piece

Lumber Defects Warp – any variation from a true board Crook – any deviation from a straight line, edge to edge Bow – any deviation flat-wise from a straight line end to end Cup – curve across the grain or width Wind or Twist – multiple defects