A circular frame, or solid disc, made of wood or metal, and turning upon an axis. There are a variety of kinds, but we shall in this place direct our attention to carriage wheels, to which the foregoing definition will best apply. The ordinary carriage wheel consists of three principal parts; namely, the nave, hub, or centre; the spokes or radii, which connect the centre to the periphery or ring. The ring is sometimes made of one entire length, bent into the circular form; but by far the most usual plan is to construct the ring of a series of curved pieces, correctly jointed endways, so as to complete the entire circle. After the ring is thus prepared, and every joint corrected and smoothed whilst placed in its true circle, the joints are bored, and an oaken dowel or pin driven into the perforations. The manufacture of the spokes consists in chopping them first to nearly their shape, and then finishing their figure by spoke-shaves; afterwards they are all gauged to an exact length, their shoulders and tenons made, the tenons that are to enter the stock being square, and those for the felloes round; and all the tenons are made a little larger towards their shoulders than at their other ends, in order that they may fit very tightly when driven up into their mortises.
The tenons in the nave depend wholly for their firmness there, to accurate workmanship; but the tenons in the felloes go through their thickness, and are then wedged up on the outside. The strength of a wheel depends greatly on the attention paid to the arrangement and framing of the spokes; in common wheels they are framed equally all round the thickest part of the nave. the tenons of the spokes being so beveled as to stand, with reference to the horizontal position of the nave, about three inches out of the perpendicular: this is done to produce what is called the dishing of the wheel. But for obtaining increased strength, the spokes of wheels, (as in those of the mail coaches,) are framed so that every other spoke shall stand perpendicular to the nave. Hence the mortices are made in two parallel lines around the nave, the other ends of the spokes entering the felloes in a single line; therefore, viewed edgeways, the position of the spokes represents two sides of an isosceles triangle, of which the axis forms the base line, (an arrangement which the uninformed will clearly understand, upon reference to the perspective figure of Jones's patent suspension wheel, given further on in this article;) this confers great stability to the wheel, at a trifling addition of cost of workmanship.
The blocks which form the naves of wheels are furnished to the wheelwright, of the size required. The wood preferred for this purpose is elm. To produce their round conical form they are turned in a lathe, with neat mouldings upon the surface. The nave is now ready to have its mortises cut; which is a work of considerable art, especially when executed in the rapid and correct manner in which they usually are, by practised workmen. In this work the wheelwright uses a very simple and efficient tool, that ispeculiar to his craft; it is called a buz, and is employed to cut out the angles of his mortises square and clean; it is a sort of double chisel, or that in which the straight edges of two common chisels are united at right angles; and it cuts out the corners, as may be supposed, very expeditiously, and so exactly that the square tenon of the spoke bites very firmly in every part. The workman fits each spoke successively, and puts a mark upon it. When they are all fitted, he begins to put the whole wheel together, fitting all the spokes to the nave first, and then adding the felloes.
In this state the wheel is put to season; that is, exposing it to a current of air for a week or two, or, as in some manufactories, placing it in a kiln for a few hours, heated to about 140o Fahrenheit. When seasoned, the whole of the wheel is examined, to ascertain if all its parts are still adapted to make solid and close joints in every part; and if found so, they are all secured and fixed, by driving up all the spokes firmly into the nave, and then putting on the felloes, and driving them down firmly upon the shoulders of the spokes; and the ends of the tenons, which come through the felloes, are then secured by wedges driven into their middles. This done, the wheelwright "cleans off;" that is, finishes the wood-work, by his planes, shaves, fish-skin, and glass-paper. The next operation is to put on the iron tire. The tire is made of flat bar iron, and of breadth and thickness proportioned to the wheel. When the tire consists of separate pieces or streaks, the bars are cut to the same length as the felloes, and curved to the radius of the wheel, and have suitable holes punched through them, to receive very stout nails, by which they are secured to the wooden ring of the wheel; and the iron tire is so placed over the felloes, as to meet in the middle of each felloe, and thus secure more effectually the joints of the latter; the tire nails pass quite through the felloes, and are rivetted on the inside of the ring, upon bars or washers, which materially strengthens the fabric.
Further to bind and compress the parts of the wheel together, the tire is put and nailed on to the wheel in a red-hot state; which burns and presses down all bumps and inequalities of the surface, and produces great solidity of structure. The best kinds of wheels, - those used for coaches and other light vehicles,-have usually their tires of one single piece or ring ready formed, which is expanded by being made hot in a circular fire, and in this state put upon the wooden periphery of the wheel, when, by its shrinking as it cools, it draws all the parts of the wheel together with irresistible force.
Many years ago a patent was obtained for making the whole wooden periphery of one entire piece, and this process is still extensively practised for the wheels of light carriages. Straight grained ash is selected and boiled or steamed, until it becomes very flexible, when it is bent on a cylinder, and fastened together whilst in its circular form.