Mr. Howard's invention has no reference whatever to the nave of the wheel, but is confined to an improved mode of combininga wheel at its periphery. He employs, as shown in the subjoined figure, representative of a small portion of a wheel, an iron ring a, as the outside tire; inside of this tire he has another ring of iron, b, which stands as a substitute for the ordinary felloes; and to this, which we will call for distinction the felloe-ring, he fastens by red-hot rivets c c, a "spoke-shoe" d d, made of the shape represented, of cast-iron, and containing a central cavity or socket, for the insertion of the end of a spoke e; of course there are as many spoke-shoes as spokes, which are arranged equidistantly around the inside of the felloe-ring; when these have been all firmly fixed in the manner of that shown, and the spokes have been all duly fitted into the nave and driven home, and the outer ends of all the spokes have been accurately gauged, and duly fitted to the sockets of the shoes, they are put or forced into the same sideways, as seen at e; this operation is performed in such a manner as to leave a space of about half an inch between the ends of the spokes and the ends of the sockets, for the purpose of wedging them up firmly.
This is effected in the following manner: - Against the squared end of each spoke is laid a thin piece of plate-irong, of the same sectional area; then is driven a slightly tapered long oaken wedge h h, the foremost end passing through a hole cast in the shoe on the opposite side: and when the cavity is thus closely filled, the projecting pieces are cut off, and a sharp iron wedge i, is then driven into the middle of the oaken wedge, so as to render the force of contact as great as possible; a plate of wrought iron, f, is then put into the cavity represented over e h i, and riveted to the shoe by long red-hot rivets passing through the whole. All the shoes and spokes being thus fitted, the tire ring is put over the whole in a red-hot state, which, shrinking as it cools, draws the whole together in a manner that gives it extraordinary solidity.
It will be observed that the principle of construction of Mr. Howard's wheels is the same as that of the common kind, in which dependence is placed entirely upon the stability of the outer ring for its cohesion; but it is a more finished and masterly production, is constructed of more tenacious materials, and is well calculated to obviate the leading defects before mentioned of the former. The advocates for Mr. Jones's wheel object to Mr. Howard's, on the ground of its not being on the tension principle. On this point we would observe, that the spokes undoubtedly are not, but that it may be fairly contended that the periphery is, as this must be torn asunder by a longitudinal pull, in order to destroy the cohesion of the wheel; and the felloe-ring alone, (which never wears,) is made of adequate strength to bear the whole strain, without any of the additional support it derives from the tire-ring; the utmost confidence may therefore be placed in the great strength and durability of Mr. Howard's wheels, however excellent may be the principle of the former invention.
A patent was recently taken out for a very strong metallic wheel, by the Messrs. Forrester, of Liverpool, consisting of a skeleton of malleable iron, imbedded or surrounded with cast iron. Such wheels are, however, necessarily very heavy, and less suited to the common road than to railways. - For a description of them, see the latter article.
We shall, however, advert in this place to another patent, - not on account of any novelty it may be found to contain, but for the twofold purpose of elucidating a process that we had imagined was commonly practised by iron-masters and tire-smiths, and of affording us an opportunity of noticing the erroneous principle upon which wheels in general are constructed.
The specification of Mr. John Meaden, of Southampton's patent, (enrolled June 1828,) states his object to be the construction of the tire or hoops of iron, which surround carriage wheels, concave on the inner surface, next to the felloes, and convex on the external surface; the objects of which are to fix the tire more securely to the wheel, and to reduce the friction produced between the periphery of the wheel and the road. The specification proceeds to describe very minutely the process of making tires, - a process which we doubt not our readers of the before-mentioned callings will recognise as a "modern antique." A common flat wrought-iron bar, of the proper width and length, is to be passed between a pair of rollers, one of which has a concave groove, and the other a corresponding convex projection, so as to compress and bend the intervening bar into the required form. The bar thus formed is next bent round into a hoop of the required size, with the concave side inwards, and then the ends are welded together. To give the hoop the desired conical figure, or "dishing," it is placed over a large cast-iron mandril, like that represented in the annexed figure, where it is hammered until it takes the required form. The letters a and b indicate hoops of different sizes.
To fix this hoop to the wheel, it is heated in a furnace of a circular form, so that the fire may act uniformly on every part. In a large wheel, this process of heating the hoop causes it to expand about one inch in circumference, and it is thereby made large enough to slip over the wooden wheel, previously prepared, of greater dimensions than the interior circle of the iron hoop, in the cold state. Whilst the iron hoop is being heated, the wooden wheel is clamped to a flat circular plate, which is fixed to a central axis, to enable it to revolve; and this axis is fixed upon an horizontal bar, by which the wheel and iron plate to which it is clamped may be turned in either a vertical or horizontal direction. Underneath the circular plate is a semicircular well or cistern, containing cold water, into which the wheel is immersed and turned round as soon as the hoop is put on it. This application of cold to the hot expanded hoop causes it to contract with irresistible force, pressing the spokes into the felloes and nave, and binding all the parts together. The annexed little figure exhibits a section of the new patent tire, as applied to the felloe d; e representing the end of a spoke.
A curved tire like the foregoing was made many years prior to Mr. Meaden's patent, but by simpler and cheaper means, - it being rolled directly from the bloom into curved bars; and we think we remember seeing them on the mail coaches more than twenty years ago. The curve on the interior side of the tire is of unquestionable advantage, in causing it to hold more securely on the felloes, - as must be evident from the preceding figure; but the external curvature of the tire is, in our opinion, of very doubtful utility. The rounding of the extreme edges of a flat-bearing wheel may prevent dirt being hitched up and carried round with the wheel; but even that much being removed, reduces to the same extent the resistance of the ground to the wheel sinking into it; and if the whole bearing surface be rounded, it must evidently penetrate deeper into the ground, and in so doing force the materials of the road sideways. Nevertheless, tire of this construction is, we believe, still employed in our mail coaches. But however injurious to the roads may be tire of this kind, the practice of giving a conical form to the rims of carriage wheels is infinitely more destructive.
This form has an evident tendency to move in a different direction to the line of draught; and the power which is required to keep it in a straight line is so much power wasted in twisting the materials of the road out of settings, and grinding them to powder.
The cylinder (as Mr. Cumming justly observes) having all its parts of equal diameter, will, in rolling on its rim, have an equal velocity at every part of its circumference, and necessarily advance in a straight line. And as all the parts of the rim have an equal velocity, none can have a tendency to drag forward or impede the progress of the others; they all advance with one consent, without the rubbing of any part on the surface on which they roll. As there is no rubbing there can be no friction, and consequently a cylinder perfectly round, hard, and smooth, forms the least possible resistance, however great its weight or the pressure on its rim. It therefore follows, that all the power that is employed in drawing forward a cylindrical body in a straight line on a compressible substance, is ultimately applied in compressing smooth and levelling the substance on which it rolls. The rolling of a cylindrical body, therefore, can have no tendency to alter the relative situation or parts of materials on which it passes, nor any how to derange them, but by a progressive dead pressure to consolidate, level, and smoothe them.
If a cylinder be cut transversely into several lengths, each part will possess all the above properties; and if the rim of a carriage wheel be made exactly of the same shape, it must necessarily have the same tendencies. When wheels with cylindrical rims are connected by an axis, the tendency of each being to advance in a direct line, they proceed in this connected state with the same harmony and unity of consent that exist in the parts of the same cylinder; but, as conical rims have been universally preferred for a series of years, it is natural to suppose that there were obvious reasons for such preference. The cone diminishing gradually from its base to its point, the velocity of every part of its circumference in rolling on an even plane, will be diminished as the diameter; and at the very point where there is no visible diameter, it will have no perceptible motion; but if the cone be made to advance in a straight line, the natural velocity of its several parts will not be as the spaces, therefore a rubbing and friction will take place at its circumference, from the different velocities of its parts, which must render the draught heavier. In rolling on paved streets nothing can be conceived more calculated for their destruction than the conical rim of a broad wheel.
See Carriages, Axletres, etc.
For Teethed Wheels employed in driving machinery, see that article.