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Defects in timber

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Defects in timber Grade 8 * * objectives What are defects in timber Types of timber defectives knots Shakes Waney edge Dry rot * knots * Knots * Knots Where a branch ... – PowerPoint PPT presentation

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Title: Defects in timber


1
Defects in timber
  • Grade 8

2
objectives
  • What are defects in timber
  • Types of timber defectives
  • knots
  • Shakes
  • Waney edge
  • Dry rot

3
knots
4
Knots
5
Knots
  • Where a branch has grown out of a tree the grain
    in the trunk becomes very twisted. When this is
    cut through during conversion the result is a
    weaker board and one which is difficult to work.
    Dead knots occur in some softwoods

6
knots
  • These are distinguished from live knots because
    they show a black line round their circumference
    and they sometimes fall out of the wood leaving a
    hole.

7
Shakes
  • These are splits along the grain of the wood.
  • Heart shakes and star shakes are very similar
    they radiate from the centre or heart (see
    drawing)

8
shakes
  • Cup or ring shakes follow the annual rings.

9
shakes
  • End splits are caused by rapid drying from the
    end grain
  • Shakes may occur during the felling or as a
    result of faulty seasoning.

10
Waney edge
  • When the outside of the tree is left as part of a
    board it is called the waney edge. .

11
Dry rot
12
Dry rot
  • This is caused by a fungus growth which lives on
    the wood and thus destroys it. It attacks wood in
    damp, unventilated positions causing it to dry up
    and crumble into dust.

13
Fungus Attack
14
Fungus Attack
  • There are some more or less harmless fungi which
    affect timber. The result is usually to stain the
    wood with grey streaks or patches. This kind of
    fungus spoils a decorative white wood like
    sycamore

15
Insect Attack
16
Insect Attack
17
Insect Attack
18
Insect Attack
  • There are several vaneties of insect that attack
    wood. One that does serious damage to furniture
    is the common furniture beetle.
  • The beetle lays its eggs in cracks and crevices
    of the wood. These hatch into small worms which
    burrow into the wood. They continue to eat their
    way through the wood for up to two years. The
    worms then change into beetles and come out
    leaving a woodworm hole.

19
Insect Attack
  • It is thus possible for wood to be affected by
    woodworm for a long time before the woodworm
    holes are seen. The beetles are very small-about
    the size of a pin head-and light brown in colour.
    They are active in the summer months and during
    this time they fly about and lay their eggs on
    furniture. They are very fond of the plywood
    backs of cupboards. Although little can be done
    about the worms in the wood, several preparations
    are on the market which poison the beetles as
    they come out and destroy any eggs laid" on the
    surface.

20
Dutch Elm Beetle.
21
Dutch Elm Beetle.
  • This is a fungus which is spread very rapidly
    through elm trees by a small beetle. The fungus
    kills the tree but the timber, though not
    perfect, can be used.

22
classwork
  • Question
  • 1. Show ,by means of sketches what you understand
    by the following star shake, knots, cup shake,
    waney edge
  • 2. Write down what you know about the common
    furniture beetle
  • 3. Name a fungus which destroys wood particular
    damp unventilated postion
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