TERM: FIRST TERM
SUBJECT: BASIC TECHNOLOGY
CLASS: JSS 3
REF MATERIALS
- EVANS BASIC TECH FOR JSS BOOK 3
- NERDC BASIC TECH FOR JSS BOOK THREE
WEEK THREE
TOPIC: PRODUCTION OF MATERIAL: WOOD
CONTENT
- Wood defects
- Veneer
- Manufactured boards
WOOD DEFECTS:
A defect in timber is any feature in timber that reduces the quality and market value of timber. Defects in timber can be grouped into two types
- The natural defects: these are the defects that occur during the growth of the tree. Examples include knots, shakes, upset grains and cross grains.
- KNOT: These occur at the point where branches grow from the trunkof trees. When the knot rot away and fall out of position it leaves what is known as knot-hole
- SHAKES: These are splits and complete separation of parts of a stem in a living tree. Shakes may be heart shake. star shakes , cup shakes and ring shakes
- The artificial defects. These are caused by careless handling faulty seasoning and preservation of wood. Artificial defects include cup, bow, twist, check and insect attack
- CUP: This is a concave curvature across the face of the timber. It is caused by bad stacking during drying. Plain sawn planksare more affected than quarter sawn.
- BOW: This is either convex or concave curvature along the length of the plank.
- TWIST: This is a spiral from of distortion along the length of the plank.
- INSECT ATTACK: These are visible minute holes seen the surface of boards.
EVALUATION
- What is wood defect?
- State the differences between natural defects and artificial defect.
- Mention three examples each o f natural defect and artificial defect
VENEER
A VENEER is a thin sheet or slice of sheet obtained from wood. The thickness of such veneer ranges from 0.5mm to 3mm.
USES OF VENEER
- It is used for manufacturing plywood.
- It is used in decorating furniture
- It is used in making faces of other types of composite boards.
METHODS OF MAKING VENEER
- ROTARY OR PEELING METHOD
- SLICING METHOD
- ECCENTRIC PEELING METHOD
ROTARY METHOD
The log of wood is mounted on a heavy lathe machine and a cutting knife peels off a continuous sheet as the log is rotating. Then the continuous sheet is later cut into the required size.
SLICING METHOD
This method involves serving the log to the lathe machine bed surface top and the slices of veneer are gotten by peeling knife back and forth. This method is used to produce decorative veneer.
ECCENTRIC PEELING METHOD
The log is first sawn to quarter log with the sapwood corner as centre. The log is mounted on the lathe machines and veneers are sliced off with cutting knife
MANUFACTURED BOARDS
Manufactured boards are man-made (artificial) wood products. They vary in sizes weight and structure.
ADVANTAGES OF MANUFACTURED BOARD OVER SOLID WOOD
- They can be made into large, flat sheets.
- They do not check and warp like solid wood.
- Some of them can be bent to form curves.
- They can be worked on and cut easily.
- They can be nailed without splitting.
EXAMPLES OF MANUFCATURED BOARDS
- PLYWOOD: This is obtained by gluing three or more sheets of veneer together.
- BLOCK BOARD: This board resembles plywood but it has a core which is made of strips usually 20mm-25mm wide and covered with two skins of veneers .It has all the quantities of plywood but cannot be bent .It is used for table tops, cupboards e.t.c
- LAMINATED BOARD: It is similar to block board but its core materials are usually thinner, being 3mm- 7mm wide. It is heavier than block board .It is used for high-class veneer furniture.
- CHIP BOARD: This is the board manufactured from wood chips. Chips are mixed with glue and pressed together under heat to form solid boards of varying thickness .It is used for kitchen furniture and panelling.
- HARD BOARD: This is made from wood (mashed wood) with hardness and holding agent’s very high temperature and compression are essential for its production.
Other types of manufactured board include:
- Particle board
- Composite board
- Batten board
EVALUATION
- Mention three ways veneer can be obtained.
- State five advantages of manufactured boards over solid wood
GENERAL EVALUATION
- What is veneer?
- Mention five examples of manufactured board
- Mention four advantages of veneer over solid wood
- Mention two uses of veneer
READING ASSIGNMENT
Read about processing material: metal
REF BOOK:NERDC BASIC TECH FOR JSS3 PG 18-21
WEEKEND ASSIGNMENT
- A thin slice of sheet obtained from wood is a ____(a) lamina (b) plank (c) plywood (d) veneer.
- The following are methods of producing veneer except ___ (a) cutting (b) peeling (c) sourcing (d) slicing
- Which of the following materials cannot be produced from wood (a) Hook (b) paper (c) cloth (d) shoe?
- Which of the following is not a manufactured board? (a) Composite board (b) block board (c) particle board (d) shopping board.
- The type of man-made board obtained by gluing three or more sheets of veneer together is called ___ (a) Hard board (b) Chip board (c) Plywood (d) Block board
THEORY
- State the advantages of manufactured board over solid wood
- Mention three uses of veneer.
