Defects in wood

The common defects occurring in the wood and it can be divided as:
1. Defects which are caused in the tree due to abnormality in the growth.
2. Defects are also caused during seasoning operation.
3. Some defects are also there due to termites or insects.

NATURAL DEFECTS

Knots:

It is the center of the irregular part of the tree. The fiber cells of tree are wrapping around it and the normal shape of the internal structure is disturbed. In presence of knots processing a timber is not so easy and due to this timber also becomes weaker in section. Types of knots are:
a. LIVE KNOTS (these occur after felling of tree)
b. DEAD KNOTS (these occurs before felling of the tree)

Knots are also classified according to their shapes.
1. Circular knot
2. Oval knot
3. Irregular knot
4. Line knot
5. Symmetrical knot
6. Group knot

Shakes

It is produced by internal and external diseases of the tree. When there is delay in cutting of a tree even after complete maturity at that time bonding materials between the grains of the tree evaporates. Sometimes the growth of tree cells from one or another portion remains dead. Shakes appears at such places. 





Types are:

a. HEART SHAKES (these defects occur generally in the old trees. A small cavity is formed at the center of the tree i.e. in heart wood)

b. RING SHAKES (these shakes are formed as cavity on the structural rings of the tree. These are generally caused by winds)

c. TWISTED SHAKES (these are continuous shakes in twisted form)

d. PERIPHERAL SHAKES (these appears on the outer part of the tree i.e. bark. It grows towards to center of the trunk.

Twisted Grains

When the trees are affected by fast winds their grains becomes twisted. The grains of the wood are not straight but are at an inclination with respect to the axis. It is very difficult to work with the tools due to twisted grains.

Ring gall

It is an uneven broken part of tree. It is generally appears where branches are cut or irregularly broken. From the broken portion there is growth of new sap wood that do not  unite with the parent wood, as such it creates a cavity between two where decay takes place.

Distortion

Due to uneven moisture inside the wood, the shape of wood is distorted. It is caused by improper seasoning. Even cracks may occur inside the wood due to distortion. Twisting and bowing occurs generally.

Surface hardening

As the outer part of the tree dries faster than the inner portion, stresses are developed on the outer surface of the wood. This causes hardening to the outer surface. Machining cannot be done easily.