Author: Haroon Khalil

The cells in living trees do not always grow perfectly vertical or straight and parallel to the length of the truck but in a sloping manner. Such an action causes the grains to slope when the timber is sawn parallel to the pitch. Such sloping grains are considered to be a defect.

The exterior surface of a tree shrinks when it is exposed to atmospheric agencies. Such a shrinkage results in cracks known as wind cracks (Fig. 10.6). Figure 10.6 Typical wind cracks of timber

These are also known as twisted grains or wandering hearts. They are caused by the twisting of young trees by fast-blowing winds. The fibres of the wood are twisted in one direction only which causes problems while sawing. However, they may be used as poles or posts without any planing (Fig. 10.4). Figure 10.4 Typical twisted…

Different kinds of defects are found in timber. Generally, they are caused by the nature of the soil on which the tree is grown, the fertility it gained during growth and changes occurred in the environment during its growth. The defects to be generally looked into while selecting timber for woodwork are discussed below. Knots…

Good timber should produce a clear ringing sound when struck. Decayed timber produces a dull and heavy sound.

The colour of quality timber should be uniform and of dark colour. Light-coloured wood usually indicates timber of low strength.

The timber should be easily workable, i.e., it should not clog the teeth of the saw. It should be capable of being easily planed. A good timber when planed shows a firm and bright appearance with a silky lustre.

Good timber should possess straight and close fibres, which signify uniformity in the timber.

Quality timber should be of heavy weight and uniform along the length under consideration.

It should be free from defects such as shakes, flaws, dead knots or blemishes of any kind.