Page 1
CHAPTER 7
TIMBER
Timber denotes wood, which is suitable for building or carpentry or
various other engineering purposes like for construction of doors,
windows, roofs, partitions, beams, posts, cupboards, shelves etc
Uses of timber:
(i) Used in the form of piles, posts, beams, lintels, door/window
frames and leaves, roof members etc
(ii) Used for flooring, ceiling, paneling and construction of
partition walls
(iii) Used for form work for concrete, for the timbering of
trenches, centring for arch work, scaffolding, transmission
poles and fencing
(iv) Used in wagon and coach building, marine installations and
bridges
(v) Used in making furniture of agriculture implements, sports
goods, musical instruments, well curbs, mortar bodies, carts
and carriages, railway sleeps, packing cases etc
7.1 Classification of trees
Depending upon their mode of growth trees may be divided in
the following two categories
(i) Endogeneous trees – These trees grow inwards and fibrous
mass is seen in their longitudinal sections. Timber from
Page 2
CHAPTER 7
TIMBER
Timber denotes wood, which is suitable for building or carpentry or
various other engineering purposes like for construction of doors,
windows, roofs, partitions, beams, posts, cupboards, shelves etc
Uses of timber:
(i) Used in the form of piles, posts, beams, lintels, door/window
frames and leaves, roof members etc
(ii) Used for flooring, ceiling, paneling and construction of
partition walls
(iii) Used for form work for concrete, for the timbering of
trenches, centring for arch work, scaffolding, transmission
poles and fencing
(iv) Used in wagon and coach building, marine installations and
bridges
(v) Used in making furniture of agriculture implements, sports
goods, musical instruments, well curbs, mortar bodies, carts
and carriages, railway sleeps, packing cases etc
7.1 Classification of trees
Depending upon their mode of growth trees may be divided in
the following two categories
(i) Endogeneous trees – These trees grow inwards and fibrous
mass is seen in their longitudinal sections. Timber from
Timber
these trees has very limited engineering applications Ex:
bamboo, cane , palm etc
(ii) Exogeneous trees: These increases in bulk by growing
outwards and used for engineering purposes.
Exogeneous trees are further sub divided into two groups
a) conifers b) deciduous
a) Conifers or evergreen trees: These trees having pointed,
needle like or scale like leaves and yield soft wood
b) Deciduous trees: The trees having flat broad leaves and
leaves of those trees fall in autumn and new ones appear
in spring season. Timber for engineering purpose is
mostly derived from deciduous trees. These trees yield
hard wood.
Ex: ash, beach, oak, sal, teak, shishum and wallnut
Comparison of softwood and hard wood
S.No. Item Soft wood Hard wood
1. Annual rings Distinct Indistinct
2. colour light dark
3. fire resistance poor more
4. modullary rays Indistinct distinct
5. Structure resinous and non-resinous
split easily & close grained
6. weight light heavy
7. strength strong for direct equally strong
Pull & weak for for resisting
Resisting thrust tension,compr
or shear -ession & shear
Page 3
CHAPTER 7
TIMBER
Timber denotes wood, which is suitable for building or carpentry or
various other engineering purposes like for construction of doors,
windows, roofs, partitions, beams, posts, cupboards, shelves etc
Uses of timber:
(i) Used in the form of piles, posts, beams, lintels, door/window
frames and leaves, roof members etc
(ii) Used for flooring, ceiling, paneling and construction of
partition walls
(iii) Used for form work for concrete, for the timbering of
trenches, centring for arch work, scaffolding, transmission
poles and fencing
(iv) Used in wagon and coach building, marine installations and
bridges
(v) Used in making furniture of agriculture implements, sports
goods, musical instruments, well curbs, mortar bodies, carts
and carriages, railway sleeps, packing cases etc
7.1 Classification of trees
Depending upon their mode of growth trees may be divided in
the following two categories
(i) Endogeneous trees – These trees grow inwards and fibrous
mass is seen in their longitudinal sections. Timber from
Timber
these trees has very limited engineering applications Ex:
bamboo, cane , palm etc
(ii) Exogeneous trees: These increases in bulk by growing
outwards and used for engineering purposes.
Exogeneous trees are further sub divided into two groups
a) conifers b) deciduous
a) Conifers or evergreen trees: These trees having pointed,
needle like or scale like leaves and yield soft wood
b) Deciduous trees: The trees having flat broad leaves and
leaves of those trees fall in autumn and new ones appear
in spring season. Timber for engineering purpose is
mostly derived from deciduous trees. These trees yield
hard wood.
Ex: ash, beach, oak, sal, teak, shishum and wallnut
Comparison of softwood and hard wood
S.No. Item Soft wood Hard wood
1. Annual rings Distinct Indistinct
2. colour light dark
3. fire resistance poor more
4. modullary rays Indistinct distinct
5. Structure resinous and non-resinous
split easily & close grained
6. weight light heavy
7. strength strong for direct equally strong
Pull & weak for for resisting
Resisting thrust tension,compr
or shear -ession & shear
Structure of tree: From the visibility aspect, the structure of a tree can
be divided into two categories
1. Macro structure
2. Micro structure
I. Macro structure: The structure of wood visible to the naked
eye or at a small magnification is called macro structure. Fig
7.1 shows the macro structure of exogenous tree.
Fig 7.1 Micro structure of exogenous tree
(i) Pith: The innermost central portion or core of the tree
is called pith or medulla
(ii) Heart wood: The inner annual rings surrounding the
pith is known as heart wood. It imparts rigidity to tree
Page 4
CHAPTER 7
TIMBER
Timber denotes wood, which is suitable for building or carpentry or
various other engineering purposes like for construction of doors,
windows, roofs, partitions, beams, posts, cupboards, shelves etc
Uses of timber:
(i) Used in the form of piles, posts, beams, lintels, door/window
frames and leaves, roof members etc
(ii) Used for flooring, ceiling, paneling and construction of
partition walls
(iii) Used for form work for concrete, for the timbering of
trenches, centring for arch work, scaffolding, transmission
poles and fencing
(iv) Used in wagon and coach building, marine installations and
bridges
(v) Used in making furniture of agriculture implements, sports
goods, musical instruments, well curbs, mortar bodies, carts
and carriages, railway sleeps, packing cases etc
7.1 Classification of trees
Depending upon their mode of growth trees may be divided in
the following two categories
(i) Endogeneous trees – These trees grow inwards and fibrous
mass is seen in their longitudinal sections. Timber from
Timber
these trees has very limited engineering applications Ex:
bamboo, cane , palm etc
(ii) Exogeneous trees: These increases in bulk by growing
outwards and used for engineering purposes.
Exogeneous trees are further sub divided into two groups
a) conifers b) deciduous
a) Conifers or evergreen trees: These trees having pointed,
needle like or scale like leaves and yield soft wood
b) Deciduous trees: The trees having flat broad leaves and
leaves of those trees fall in autumn and new ones appear
in spring season. Timber for engineering purpose is
mostly derived from deciduous trees. These trees yield
hard wood.
Ex: ash, beach, oak, sal, teak, shishum and wallnut
Comparison of softwood and hard wood
S.No. Item Soft wood Hard wood
1. Annual rings Distinct Indistinct
2. colour light dark
3. fire resistance poor more
4. modullary rays Indistinct distinct
5. Structure resinous and non-resinous
split easily & close grained
6. weight light heavy
7. strength strong for direct equally strong
Pull & weak for for resisting
Resisting thrust tension,compr
or shear -ession & shear
Structure of tree: From the visibility aspect, the structure of a tree can
be divided into two categories
1. Macro structure
2. Micro structure
I. Macro structure: The structure of wood visible to the naked
eye or at a small magnification is called macro structure. Fig
7.1 shows the macro structure of exogenous tree.
Fig 7.1 Micro structure of exogenous tree
(i) Pith: The innermost central portion or core of the tree
is called pith or medulla
(ii) Heart wood: The inner annual rings surrounding the
pith is known as heart wood. It imparts rigidity to tree
Timber
(iii) Sap wood: The cuter annual rings between heart
wood and cambium layer is known as sap wood
(iv) Cambium layer: Thin layer of sap between sap wood
and inner bark is known as cambium layer
(v) Inner bark: The inner skin or layer covering the
cambium layer is known as inner bark
(vi) Outer Bark: The outer skin or cover of the tree is
known as outer bark
(vii) Medullary rays: The thin radial fibres extending
from pith to cambium layer are known as medullary
rays
II. Micro structure: The structure of wood apparent only at
great magnifications is called micro structure under micro
scope, it becomes evident that the wood consists of living and
lead cells of various sizes and shapes.
7.2 Defects in Timber:
Defects occurring in timber are grouped into the following
divisions.
a) Defects due to conversion: During the process of converting
timber to commercial form, the following defects may occur.
(i) Chip mark: mark or sign placed by chip on finished
surface of timber
(ii) Diagonal grain: Due to improper sawing of timber
Page 5
CHAPTER 7
TIMBER
Timber denotes wood, which is suitable for building or carpentry or
various other engineering purposes like for construction of doors,
windows, roofs, partitions, beams, posts, cupboards, shelves etc
Uses of timber:
(i) Used in the form of piles, posts, beams, lintels, door/window
frames and leaves, roof members etc
(ii) Used for flooring, ceiling, paneling and construction of
partition walls
(iii) Used for form work for concrete, for the timbering of
trenches, centring for arch work, scaffolding, transmission
poles and fencing
(iv) Used in wagon and coach building, marine installations and
bridges
(v) Used in making furniture of agriculture implements, sports
goods, musical instruments, well curbs, mortar bodies, carts
and carriages, railway sleeps, packing cases etc
7.1 Classification of trees
Depending upon their mode of growth trees may be divided in
the following two categories
(i) Endogeneous trees – These trees grow inwards and fibrous
mass is seen in their longitudinal sections. Timber from
Timber
these trees has very limited engineering applications Ex:
bamboo, cane , palm etc
(ii) Exogeneous trees: These increases in bulk by growing
outwards and used for engineering purposes.
Exogeneous trees are further sub divided into two groups
a) conifers b) deciduous
a) Conifers or evergreen trees: These trees having pointed,
needle like or scale like leaves and yield soft wood
b) Deciduous trees: The trees having flat broad leaves and
leaves of those trees fall in autumn and new ones appear
in spring season. Timber for engineering purpose is
mostly derived from deciduous trees. These trees yield
hard wood.
Ex: ash, beach, oak, sal, teak, shishum and wallnut
Comparison of softwood and hard wood
S.No. Item Soft wood Hard wood
1. Annual rings Distinct Indistinct
2. colour light dark
3. fire resistance poor more
4. modullary rays Indistinct distinct
5. Structure resinous and non-resinous
split easily & close grained
6. weight light heavy
7. strength strong for direct equally strong
Pull & weak for for resisting
Resisting thrust tension,compr
or shear -ession & shear
Structure of tree: From the visibility aspect, the structure of a tree can
be divided into two categories
1. Macro structure
2. Micro structure
I. Macro structure: The structure of wood visible to the naked
eye or at a small magnification is called macro structure. Fig
7.1 shows the macro structure of exogenous tree.
Fig 7.1 Micro structure of exogenous tree
(i) Pith: The innermost central portion or core of the tree
is called pith or medulla
(ii) Heart wood: The inner annual rings surrounding the
pith is known as heart wood. It imparts rigidity to tree
Timber
(iii) Sap wood: The cuter annual rings between heart
wood and cambium layer is known as sap wood
(iv) Cambium layer: Thin layer of sap between sap wood
and inner bark is known as cambium layer
(v) Inner bark: The inner skin or layer covering the
cambium layer is known as inner bark
(vi) Outer Bark: The outer skin or cover of the tree is
known as outer bark
(vii) Medullary rays: The thin radial fibres extending
from pith to cambium layer are known as medullary
rays
II. Micro structure: The structure of wood apparent only at
great magnifications is called micro structure under micro
scope, it becomes evident that the wood consists of living and
lead cells of various sizes and shapes.
7.2 Defects in Timber:
Defects occurring in timber are grouped into the following
divisions.
a) Defects due to conversion: During the process of converting
timber to commercial form, the following defects may occur.
(i) Chip mark: mark or sign placed by chip on finished
surface of timber
(ii) Diagonal grain: Due to improper sawing of timber
(iii) Torn grain: Due to falling of tool small impression is
formed
(iv) Wane: Presence of original rounded surface on the
manufactured piece of timber
b) Defects due to fungi: The attack of timber by fungi when
moisture content of timber is above 20% and presence of air and
warmth for the growth of fungi the following defects are caused
(i) Blue stain: Sap of wood is stained to bluesh colour
(ii) Brown rot: Decay or disease of timber by removal of
cellulose compounds from wood and wood assumes the
brown colour
(iii) Dry rot: Convert the wood into dry powder form
(iv) Heart rot: This is formed when branch has come out of a
tree and the tree becomes weak and gives out hallow
sound when struck with a hammer
(v) Sap stain: The sap wood looses its colour because of feed
on cell contents of sap wood.
(vi) Wet rot: Caused chemical decomposition of wood of the
timber and timber converts to grayish brown powder
known as wet rot.
(vii) White rot: Attack lignin of wood and wood assumes the
appearance of white mass
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