LESSON 5 - WOODS & PLASTICS

• plain sawn lumber - a variety of noticeable grain patterns •Tends to twist and cup, and wears unevenly •Tends to have raised grain •Shrinks and swells less in thickness, more in width.
• quarter sawn lumber - has more even grain patterns •Wears more evenly with less raised grain and warping •shrinks and swells less in width, more in thickness.
• Identify the given image:

  plain sawn lumber

  
• Identify the given image:

  quarter sawn lumber

  
• Natural wood has certain properties that make it an attractive building material:

  • natural warmth
  • workability
  • infinite variety
  • flexibility
  • fire protection
  • color
• natural warmth - to the touch; wood insulates
• workability - easily shaped with simple tool
• infinite variety - no two trees, or even pieces from the same tree, are alike
• flexibility - watch how huge trees bend before the wind
• fire protection - wood chars and therefore burns slowly, doesn’t melt or crumble
• color - natural, through wood’s ability to receive many types of stains and finishes
• Classification of wood:

  • Softwood
  • Hardwood
• softwoods - come from the conifers (evergreens) which have needles instead of leaves
• hardwoods - come from the broad-leaved or deciduous trees. Most Philippine timber are of this latter kind
• STRUCTURE OF WOOD:

  • sapwood
  • heartwood
• sapwood - is the softer, younger outer portion of a tree. It is more permeable, less durable
• Identify the image:

  sapwood

  
• sapwood - the portion of the log near the periphery. Contains living cells and takes an active part in the life process of a tree.
• heartwood - the older, harder central portion of a tree. Is denser, less permeable and more durable than the surrounding sapwood.
• Identify the image:

  heartwood

  
• PROPERTIES OF WOOD:

  • hardness
  • flexibility
  • strength
  • durability
• hardness - This is measured by the compression which a piece of timber undergoes when a weight is applied to it.
• flexibility - The amount of piece will bend before breaking . Softwoods are generally brittle while most hardwoods are flexible.
• DEFECTS OF WOOD:

  • decay
  • checks
  • shakes
  • knots
  • pitchpockets
  • wane
  • warping
• decay - Caused by the attack of fungi.
• checks - Cracks or lengthwise separation across the annual rings of growth caused by irregular shrinkage during drying.
• shakes – These are cracks between and parallel to the annual rings of the growth.
• knots – These are irregular growths in the body of a tree which interrupt the smooth curve of the grain.
• pitchpockets – These are well-defined openings between annual rings containing solid or liquid pitch.
• wane – This is the lack of wood on the edge or corner of a piece.
• warping - Any variation with the plane surface of the piece caused by unequal shrinkage of the board.
• crook – a distortion of the board in which the edge is convex or concave longitudinal.
• bow – a distortion of the board in which the face is convex or concave longitudinal.
• cup – a distortion of the board in which the face is convex or concave across the board.
• twist – a distortion of the board in which one corner is raised.
• Identify the Image:

  decay

  
• Identify the Image:

  shakes

  
• Two types of Knots:

  • spike knot
  • round knot
• Identify the Image:

  pitchpockets

  
• There are several forms of warp:

  • crook
  • bow
  • cup
  • twist