Conversion of timber



Conversion is a term used to describe the cutting of wood into planks. The 'through and through' cut or slash-sawn log. This is the most economical form of cutting timber but there is a greater tendency to warping. In C and D you will see two methods of quarter cutting. The center picture shows the more common form when the center is 'boxed out', that is cut away. Quarter cutting is used in oak in order to show the silver grain or medullary rays.

Shrinkage

The greatest amount of shrinkage takes place in the tangential direction of the log, which means along the line of the annual rings at a tangent to the circumference of the log. The radial shrinkage is only half as much. In black shading the relative shrinkage of a slash-sawn and quarter-sawn board. Uneven drying causes uneven shrinkage and various splits and checks can develop. Two examples, star-shakes and end splits, are illustrated.

Fungal decay and insect attack

In the ordinary way, fungal decay and insect attack are not likely to trouble the wood carver. However, you can, if you wish, treat your carving with a wood preservative when the work is completed.

Fungus, the chief cause of decay in timber, is a plant and needs organic material to maintain life. It must also have moisture and oxygen so that wood kept dry will not be attacked. Whereas it is highly unlikely that your carving will be attacked by fungi, insect pests can easily move from infected furniture to your work.

The most common of these pests is the furniture beetle (anobium punctatum), often known as 'wood worm'. During June and until August the beetles emerge from the wood looking for new homes in any suitable cracks and crevices in timber.

Both hard- and softwoods are vulnerable. The insects then lay their eggs. These eventually hatch into larvae a quarter of an inch long. With powerful jaws these grubs bore into the wood. This process goes on for as long as eighteen months when the grub pupates and the whole cycle commences again. It is possible to treat wood with chemicals toxic to both fungi and insects. There are a number of proprietary brands on the market.

Durability of wood

The durability of wood is not related to its hardness or softness. When the term is used in the timber trade, it refers to the wood's reaction to climate, weather conditions, contact with the ground, immersion in water, etc. Wood carvings are, as a rule, under roof protection and it will therefore be only on occasion that a carver must consider durability as a factor in his work.

Timbers grown in the United States, such as oak and elm, are durable woods. Some softwoods are extremely durable, as for instance red cedar, which is more durable than oak. Resins, tannin and aromatic oils in the wood form together an effective preservative.

We can avoid the damage of the wood by recognizing its condition. Recognize the type of wood which you have and the condition of the place where you have to store your logs, this will help you to maintain the condition of the woods or logs for longer period of time.