306 BORING CYLINDERS. he constructed to supply steam to the engine for draining the docks at Cronstadt, weighed upwards of fifteen and a half tons. The increasing demand for the ponderous machinery of steam-engines having led capitalists to the erection of numerous foundries in different parts of the kingdom, their emulation was greatly instrumental in improving the art of casting and finishing cast-iron ware. Carron, the first establishment in regard to magnitude, continued also to be the most celebrated for the general excellence of its productions; and it more especially enjoyed a great reputation for the truth with which its cylinders and pumpbarrels were bored and polished. The method usually followed was that employed from time immemorial for boring the wooden pipes or pump trees, used to convey water. The pipe, placed in a carriage, was made to move forward as accurately as could be in the direction of its axis, and to press against the face of the borer; this was a tool constructed of several cutters firmly fixed in a solid wheel, which was made to revolve by the power of horses or a waterfall; and as the cutter excavated the centre of the pipe, the frame moved forward so as to keep the tree pressed against the tool. But notwithstanding the proportions and modifications which Smeaton introduced into the boring-engine he designed for Carron, and which gave the superiority to the cylinders and pumpbarrels fabricated in this foundry, over those sent from rival establishments, still the form of the cylinder, when drawn from the mould, influenced more or less that which it could receive from the action of the borer. Much of the advantage which now began to be experienced by engineers, from a greater atten WILKINSON'S BORER. 307 tion paid to the mode of finishing pipes and cylinders, would have, in truth, been greatly circumscribed in their importance, but for an invention of Mr. John Wilkinson, the proprietor of iron works at Bersham near Chester. In this beautiful contrivance, provided there was a sufficient thickness of metal, the want of truth in the casting of a hollow vessel was quite immaterial; for Wilkinson made his borer advance into the cylinder along an inflexible rod, which was fashioned with the greatest possible truth. So that the tool must excavate in a line as true as that which was formed by the rod which guided it; and this, without question, was one of the most important improvements which had been introduced into the machinery for the manufacture of machines. Indeed, so universal was its application, that it may be considered as forming an era in their manufacture, as having laid the foundation of all the wonders which have since been achieved, in giving the utmost accuracy and beauty to implements and machines of every kind, and of every variety of construction. But in nothing was its importance more clearly seen, than in the fabrication of the parts of steamengines. Cylinders of five and six feet in diameter, and piston rods of corresponding sizes, could be formed by its agency with the greatest truth, and as much precision as before its introduction it was possible to give to the small cylinders of airpumps. Watt speedily availed himself of his friend's improvement; and by having his rods and pumps properly bored and polished, he may be said now, for the first time, to have had it in his power to give comparative perfection to his own invention. For even the excellent workmanship of the Carron cylinders was so much surpassed by those 308 66 WILKINSON'S CYLINDERS. made at Bersham, that when a new engine, on the condensing principle, was to be erected at Carron itself, Bolton writes to the chief of the establishment, that he must either change his mode of boring cylinders, or get one bored by Wilkinson," for he has," says he," lately bored us some nearly without error; one which we have put up at Tipton, fifty inches in diameter, does not err the thickness of an old shilling in any part;" and in a letter from Watt to Smeaton, he says, so great has been the improvement made by Wilkinson, that he can promise upon a cylinder, having a diameter of seventy-two inches, not being further distant from absolute truth in the worst part than a thin sixpence." But even this deviation (about the fortieth of an inch) was greater than could be found in these ponderous vessels; for from the admirable nature of the process, it was next to impossible that so great an error could be produced in a vessel, of however large dimension. |