The document discusses various natural defects that can occur in timber, including burls, callus, chemical stains, coarse grain, dead wood, druxiness, foxiness, knots, rind galls, shakes, twisted fibers, upsets, water strain, and wind cracks. Knots are further classified based on size and type. Shakes are classified into cup, ring, heart, star, and radial shakes. The defects are caused by natural forces like injury, chemical reactions, rapid growth, fungi, poor ventilation, and exposure to wind and water. Timber with these defects may have reduced strength, durability, and suitability for uses like engineering.

1. DEFECTS DUE TO
NATURAL FORCES---
TIMBER
presentationby KIRTHIGA.E

2. THE MAIN NATURAL FORCES CAUSING DEFECTS IN TIMBER ARE :
 Burls
 Callus
 Chemical stain
 Coarse grain
 Dead wood
 Druxiness
 Foxiness
 Knots
 Rind galls
 Shakes
 Twisted fibres
 Upsets
 Water strain
 Wind cracks

3. BURLS :
 They are particularly formed
when a tree recieves shock or
injury in its young age.
 Due to its injury,the growth
of tree is completely upset and
irregular projections appear
on the body of timber
 These are also known as excrescences.

4. CALLUS :
 It indicates soft tissue or
skin which covers the wound
of a tree

5. CHEMICAL STAIN :
 The wood is sometimes
Discoloured by the chemical
action caused withit by some
external agency.

6. COARSE GRAIN :
 If the tree grows rapidly,
the annual rings are widened.
 It is known as the coarsed
grain timber
 such timber possesses less
strength

7. DEAD WOOD:
 The timber which is
Obtained from dead
standing trees contains
deadwood.
 It is indicated by light
weight and reddish
colour.

8. DRUXINESS:
 This defect is indicated by
white decayed spots which
are concealed by healthy wood
they are probably formed by
access of fungi.

9. FOXINESS:
 This defect is indicated by
red or yellow tinge in wood
or reddish brown stains or
spots round the pith of tree
discolouring the timber
 it is caused either due
to poor ventilation during
storage or by timber .

10. KNOTS :
These are the bases of branches or limbs which
are broken or cut off from the tree.
 The portion from which the branch is removed
recieves nourishment from the stem fora pretty
long time .
 And it ultimately results in formation of
dark hard rings which are known as knots.
 As continuity of wood fibres are broken by
knots,they form a source of weakness

11. CLASSIFICATION OF KNOTS BASED ON SIZES :
 PIN KNOT:-diametre upto 6.50mm
 SMALL KNOT:-diametre upto 6.5 and 20mm
 MEDIUM KNOT:-diameter between 20 and 40mm
 LARGE KNOT:-diameter greater than 40mm

12. Classification of knots on basis of form and quality
 DEAD KNOT:-knot which is seperated from body of wood.it
is notsafe to use wood with such a knot for engineering
purposes.
 DECAYED KNOT:-popularly known as unsound knot and
form by action of fungi on wood.
 LIVE KNOT:-it is thoroughly fixed in wood and cannot
seperated outfrom body of wood.it is free from cracks and
decay.wood containing this knot can be used for
engineering purposes.
 LOOSE KNOT:-it is preliminary stage of dead knot.
 ROUND KNOT:-the cross-section of this type of knot is
either roundor oval
 TIGHT KNOT:-it is preliminary stage of live knot.the fibres
of knot arefirmly held in sorrounding wood.

13. RIND GALLS :
 the rind means bark and gall indicates
abnormal growth.
 hence peculiar curved swelling found
on the body of tree are known as rind
gall.
 they develop at points from where
branches are improperly cut off or removed.
 they are rarely found in a tree and the timber in this
part is very weak and not durable.

14. SHAKES :
 Cup shakes
 Ring shakes
 heart shakes
 Star shakes
 Radial shakes

15. TWISTED FIBRES:
 these are known as wandering
hearts
 and caused by twisting of young
trees byfast blowing wind.
 the timbers with twisted fibres
is unsuitable for sawing
UPSETS:-
 these indicate wood fibres which
are injured by crushing or compression.
 the upsets are mainly due to improper
felling of tree and exposure of tree in
its young age to fast blowing wind

16. WATER STAIN :
 The wood is sometimes dis-
-coloured when it comes into
contact with water .
 This defect is usually found in
converted timber
Wind cracks :
 if wind is exposed to atmospheric
agencies, its exterior surface shrinks.
 Such shrinkage result into cracks.