Best Woods for Joinery & Woodworking
Before undertaking practical work in the art of joinery, it is desirable that the amateur should possess some knowledge of the nature and peculiarities of the woods most suitable for his use in the construction of articles of furniture, such as are set forth in the pictures of this manual. A good deal of success depends on the wood selected, in each case, because some woods are easy to work, while others, owing to their hardness and the irregular character of their grain, require considerable skill and practice to manipulate them satisfactorily. It may be said that the amateur, and the beginner especially, should prefer to use woods which are comparatively soft, and have grains which lie, for the most part, evenly and in one direction in any one piece: such woods are, accordingly, easy to cut and dress cleanly. All the more desirable woods are fully described and otherwise commented on in the list given in here.
The following particulars respecting the nature of wood generally may be of some value and interest to the amateur joiner. All the woods used in cabinetwork in England are the produce of the class of trees designated Exogens signifying their mode of growth ; namely, from the central part (or pith} outwards. The pith is composed of cellular tissue, which in young stems is succulent and full of fluid, but which in the course of time becomes dry and charged with air. The size of the pith varies considerably; for instance, in the ebony and boxwood trees it is very small, while in the elder it is large. Immediately around the pith lies a fibro-vascular layer, called the medullary sheath. Between the vessels of this sheath the medullary rays from the pith pass into the wood of the tree. The layers of wood are formed outside the medullary sheath in concentric layers. On account of this outward mode of formation of wood layers, deposited year after year, the stem increases indefinitely. This regular concentric formation has given rise to another name, Cyclogens, to this class of trees.
The woody layers vary in their texture at different periods of growth. At first all the tissues are pervious and charged with fluid ; but by degrees they become thickened, and the channels of the vessels get filled up and disappear. The first formed layers are, naturally, those which soonest become thus compacted and hardened. In old trees there is a marked division between the inner heart-wood, or duramen, and the outer sap-wood, or alburnum,the former being hard and dense, and often coloured, with its tubes thickened and dry; while the latter is less dense, of a paler colour, and has its tubes permeable by fluids, hence its name, sap-wood. The difference of colour between the duramen and the alburnum is often very marked. In the ebony tree the duramen is black (the only useful portion), while the alburnum is of a very light colour. In the beech the heart-wood is light brown; in the oak deep-brown; in the laburnum greenish, and in the box and fustic trees yellowish. In certain trees of temperate climates, which yield "white wood", such as the poplar and willow, no difference of colour appears. The relative proportion of alburnum and duramen varies in different trees. For good work no sap-wood should be used.
From the mode in which the woody layers are formed, it is evident that each vascular zone or ring is moulded upon that which preceded it; and as each ring is completed in the course of one year, the age of a tree can be determined by counting the concentric rings between the pith and the bark.
The accompanying picture above, represents a transverse section of an oak tree eight years old, having eight woody layers. This mode of computation is usually reliable; but from some irregularity in growth more than one ring may be formed in one year. In the section the concentric layers are shown separated by distinct lines. In trees of this class the pith is not invariably in a central position. The layers of wood may be thicker on one side than on the other, in consequence of their fuller exposure to light and air, or the nature of the nourishment conveyed. When this is the case the pith becomes eccentric. The layers vary in size in different kinds of trees, and at different periods of their growth. Soft-wooded trees have usually thick rings; and old trees form thinner rings than young ones.
Between the outer ring and the bark, there is a layer of thin-walled cells in which the protoplasm and cell-sap remain, and consequently they are capable of division and growth. This cellular layer is called the cambium: it marks the separation between the wood and the bark, and contains the active formative tissue of the tree. It constitutes the thickening zone, by means of which the stem is enlarged, the inner cells being subservient to the purposes of wood formation, while the outer cells give origin to the new bark.
While the bark and the pith become, year by year, more and more separated by the intervention of the vascular bundles, the connection between them is kept up by means of processes called medullary rays or plates. These form the "silver grain" in wood, so conspicuous in oak : they communicate with the pith and the cambium. They consist of cellular tissue, which becomes compressed and flattened so as to form a muriform appearance. In their earliest stage they occupy considerable space, but as the vascular bundles increase they become more and more compressed, forming thin laminae or plates which separate the woody bundles.
On making a transverse section of a stem, the medullary rays will be seen radiating from the centre, or the pith, towards the cambium, in the manner indicated by the radiating lines in the picture of the oak tree. The primary medullary rays extend completely from the pith to the bark; but there are others which only extend through certain of the annual rings, as indicated, and are called secondary rays; these immensely increase the number of rays, adding richness to the figure or silver grain of the wood. The effects produced by the medullary rays depend on the directions in which planks are cut from the stem.
List of the different types of woods and their properties discussed in this section:
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