The materials employed in coach-building number a great many: various kinds of wood—ash, beech, elm, oak, mahogany, cedar, deal, pine, &c.; hides, skins, hair, wool, silk, glue, whalebone, ivory, &c.; iron, steel, copper, brass, lead, tin, glass, &c.
The timber principally used in the construction of carriages is the ash. This is not an elastic, but rather a tough and fibrous wood, capable of altering its form by the application of pressure, and therefore when not in large masses requires iron plates to secure it. By boiling it becomes very pliable, and may be formed into almost any shape, provided that it is not too thick. For this purpose it is better to use steam than boiling water, as the latter is likely to dissolve and carry off the gluten which unites the fibres, thus rendering the timber useless. Some ash timber is white at heart, and some red; the white is usually the strongest and best. Some trees which have been grown on hillsides much exposed to constant winds present a remarkably wrinkled appearance through their whole length, and it is scarcely possible to plane their timber smooth; this is the toughest of all ash timber. Parts of ash-trees are sometimes found of a yellowish-brown colour, accompanied by a fetid acid smell. This is sometimes attributed to the effect of lightning, but more probably it is a putrid fermentation of the sap, owing to imperfect drying. All other circumstances being equal, the timber is best which is cut down when the circulation of the sap is slowest, as the pores are then open. In the process of drying or seasoning the bulk diminishes considerably. One of the qualities which render ash peculiarly fit for carriage construction is the absence of elasticity, and consequent indisposition to alter its form by warping or twisting. It is not well adapted for boards or planks in which much width is required, as in drying it cracks a great deal. The diameter of ash-trees used by carriage-builders varies from 1 foot to 3 feet 6 inches. It should be borne in mind in cutting ash, that the interior and the outer casing under the bark are rather softer and less durable than the parts between them.
Beech is sometimes used by carriage-builders and by wheelwrights, on account of its cheapness; but it is very liable to warp and rot, and consequently unworthy of the attention of the conscientious manufacturer.
Elm is largely used for planking where strength is required. The grain is wavy, hard to work, brittle, and apt to split without care. It is not a good surface to paint on, as the grain shows through several coats of colour. It is also used for the naves or stocks of wheels.
Oak is used for the spokes of wheels. The best kinds are made from the timbers of saplings, which are not sawn but cleft, in order that the grain may be not cut across and render the spoke unfit to resist the strains it will be subject to. Spokes are also made from the limbs of large trees.
Mahogany is largely used for panels, as when painted it shows a very even surface. There are two kinds, the “Spanish” and the “Honduras.” The former is unfit for the purposes of the carriage-builder. It is heavy and very difficult to work, requiring special tools for this purpose, as the edges of ordinary tools are rapidly destroyed by it. The Honduras is very much lighter and cheaper than Spanish, and the grain and colour more even. It takes the sweeps and curves required for body-work very easily. It can be procured up to 4 feet in width, straight-grained, and free from knots and blemishes.
A coarse-grained species of cedar is brought from the same district as Honduras mahogany, and is sometimes used for panels which have to be covered with leather, &c. Its extreme porosity renders it unfit for the application of paint.
Deal is largely used for the flooring of carriages, and for covered panels, and for any rough work that is not exposed to great wear and tear.
The wide American pine is chiefly used in very thin boards to form the covered panels and roofing of carriages.
Lancewood is a straight-grained, elastic wood, but very brittle when its limit of elasticity is reached. It comes from the West Indies in taper poles about 20 feet long and 6 or 8 inches diameter at the largest end. It was formerly much used for shafts, but since curved forms have been fashionable it has fallen into disuse. It can be bent by boiling, but is a very unsafe material to trust to such an important office as the shafts.
American birch is a very valuable wood for flat boarding, as it can be procured up to 3 feet in width. It is of a perfectly homogeneous substance, free from rents, and with scarcely a perceptible pore. It works easily with the plane and yields a very smooth surface, and the grain does not show through the most delicate coat of paint. Its chief disadvantage is its brittleness, which will not permit of its being used for any but plane surfaces, and some care is required in nailing and screwing it.
Hides are used chiefly for coverings, but also in some parts strips are used for the purposes of suspension. The hides are those of horses and neat cattle. For covering they are converted into leather by the action of oak and other bark. They are afterwards smoothed and levelled by the currier, and sometimes split into two equal thicknesses by machinery. They are then rendered pliable by the action of oil and tallow, and finished to a clear black or brown colour as may be required. This is called dressed leather. For some purposes the hides are merely levelled, put on wet to the object they are intended to cover, and left to shrink and dry. Others are covered with a coat of elastic japan, which gives them a highly glazed surface, impermeable to water; in this state they are called patent leather. In a more perfectly elastic mode of japanning, which will permit folding without cracking the surface, they are called enamelled leather. They are generally black, but any colour desired may be given to them. All this japanned leather has the japan annealed, somewhat in the same mode as glass. The hides are laid between blankets, and are subjected to the heat of an oven raised to the proper temperature during several hours.
The skins used are those of the sheep and goat. The former are converted into leather by the action of oak bark. In one form of dressing them they are known as basil leather, which is of a light brown colour and very soft. Sometimes they are blacked, and occasionally japanned like the hides. In all these forms sheep skins are only used for inferior purposes, as mere coverings, where no strength is required.
Goat skins are used in the preparation of the leather known as “Spanish” and “Morocco.” They are not tanned in oak bark like other leather, but very slightly in the bark of the sumach-tree. They pass through many processes previous to that of dyeing, for which purpose they are sewn up with the grain outwards and blown out like a bladder. This is to prevent the dye from getting access to the flesh side. This beautiful leather was originally manufactured by the Moors, who afterwards introduced the process into Spain, by which means it came to be known under two names. The English have greatly improved on the manufacture, so much so that few others can vie with it. These skins are used for the inside linings of carriages.
Hair is used as an article of stuffing. To give it the peculiar curl which renders it elastic, it is forcibly twisted up in small locks, and in that state baked in an oven to fix it. Horse-hair is the best, being the strongest and longest; but various other kinds are used. Sometimes it is adulterated with fibres of whalebone. Doe-hair is also much used as an article for stuffing, but as it is very short it cannot be curled, and there is not much elasticity in it.
Wool in its natural state is not used for carriage purposes. In the form of “flocks,” which are the short combings and fibres produced in the process of manufacturing it, it is very largely used for stuffing. In its manufactured state wool is used in great quantities, as cloth, lace, fringe, carpeting, &c.
The iron used is that known as wrought iron. To judge of its quality break a piece over the anvil; if it breaks off brittle it is of no use for the purposes it is required for. If it is good wrought iron the fracture will present a bluish, fibrous, silky texture, without any crystalline portions. Inferior iron will either appear bright and glistening (when it partakes of the properties of cast iron) or dull and greyish in tone at the fracture.
It may also be tested by bringing it to a red heat and bending it, when any flaws, &c., will at once become apparent.
Cast iron is also used in the shape of axle-boxes.
Great quantities of wrought iron are used in the construction of modern carriages. One of the best qualities is that known as the “King and Queen,” so called from its brand. This iron is manufactured from pieces of old iron, called scrap iron, which are placed in furnaces and welded under a heavy tilt-hammer, after which it is passed between rollers and converted into bars.
Steel also enters largely into carriage construction in the shape of springs, &c. Axles are made of Bessemer steel, and are found to wear very well. Steel consists of iron in which is combined a large proportion of carbon; the more carbon the higher the elasticity of the steel. If steel is over-heated, it gives up a portion of its carbon and approaches once again its original form of iron.