CONVERSION OF TIMBER
The cutting up of timber to form planks, battens, etc. of required sizes by saw is called conversion. Power machines are employed in several stages when working on a large scale. During conversion the allowance should be made for shrinkage, squaring and planning. It is about 3 mm to 6 mm. The conversion should be carried out in such a way that there is minimum wastage of useful timber. The wooden beams should be sawn in such a way that they do not contain pith in their cross-section. Strong pieces are obtained from timber when saw cuts are tangential to the annual rings and more or less parallel to the direction of medullary rays.
The way that the log is cut will depend upon several factors, some of which are:
- The type and size of the sawing machine
- The size and diameter of the log.
- The condition of the log.
- The timber species
Timber may generally be sawn in one of the following ways:
1. Ordinary sawing:
The log is moved backward and forward on the platform of a sawmill. It is very easy, quick & economical method and wastage of useful timber is minimum. But the planks obtained by this method are liable to warp and twist as a result of unequal shrinkage.
2. Radial sawing:
The sawing done parallel to the medullary rays and perpendicular to the annular rings. The
cut section shrinks at a uniform rate and the warping is therefore less. This method is used for
conversion of hard timber. The wood can be used for high-quality timber works. The wastage of
wood is more in this method and it takes a longer time for conversion.
3. Tangential sawing:
The sawing is done at right angles to the medullary rays and tangential to the annular rings
Due to the cutting of the medullary rays, the sections cut become weaker.
4. Quarter sawing:
The log is first divided into form quadrants. The saw cuts are at right angles to each other. In
this method, there is a tendency for the timber to bend in a transverse direction.
ADVANTAGES AND DISADVANTAGES OF TIMBER
The advantages of timber are :
2. It is easily available and can be quickly transported by simple means.
3. It is light in weight.
4. The floor joints in an average dwelling weighs less than rolled steel beams of equal strength.
5. The individual units of wooden dwelling are light enough so that they may be assembled by a small crew of men without special machinery
6. Boards may be cut rapidly by a saw and fastened firmly together with nails.
7. It is a good insulator of heat and sound.
8. When properly protected timber structures may give good service for a hundred of years.
9. It stands shocks and bumps, a good deal better than iron and concrete
10. On account of its lightweight. timber is generally preferred for building works
- It is combustible
- Timber swells and undergoes shrinkage
- Timber is decayed by fungi and by insects.