2. BORING or CYLINDERS for steam-engines, and for blowing machines, and the boring of the Working barrels of large pumps, and other hollow cylinders in which pistons are to work, is performed by making the steel-cutters describe a cylindrical surface on the inside of the cylinder, whilst the cy linder remains fixed. The first steam-engine cylin ders in this country were of brass, or of a mixture of copper and tin ; this was the case with the cylinder of the steam-engine, erected in the early part of the eighteenth century, for lifting water from the col liery of Elphinston in Stirlingshire. But, since that ;hue, the construction of steam-engines, and the ma nufactory of cast-iron, have been greatly improved ; the uses of both have been much extended ; and cast, iron has now for a long time been the only material employed in making cylinders for steam-engines, and other large cylinders in which pistons are to Move.
In the boring of cylinders, the steel-cutters are fixed in a cutter-head, which revolves with the bor ing bar at the same time that it is impelled along the interior surface of the cylinder by a rack, with a pi nion moved by a lever and weight as already de scribed. •The axis or boring-bar, employed for cylinders, is a hollow tube of cast-iron, and bas a groove passing through it : the length of this groove is proportioned to the length of the cylin der to be bored. The cutter-head consists of two cast-iron rings, the first of which Is accurately fitted on the boring-bar, which is turned truly cylin drical, so that this ring may slide along the boring bar ; the second rinf is fixed round the first by wedges its diameter is proportioned to the diameter of the cylinder to be bored; on its circumference are eight notches to receive the steel-cutters, which are fixed in by wedges. The first ring is fixed on the boring-bar, so as to make the whole cutter-head move round with the boring-bar, by means of two small iron bars, which go through notches in the first ring, and pass through the groove of the boring bar. These small bars have each a round hole in the part which passes through the geometrical axis of the boring-bar ; through these round holes there rases a bolt, which forms the end of the rack ; a key is put through the end of the bolt, which prevents the rack from being drawn back by the lever and weight ; and by this means, the rack impelled by the lever and weight pushes forward the cutter-head, which is at the same time revolving with the boring bar : the connection of the rack and cutter-head be ing round, and in the axis of motion, the rack is thereby free ftom the circular motion of the cutter head. This mode of constructing the boring-bar
.was invented in the works of Mr Wilkinson, at the time when accurately bored cylinders came to be required in consequence of Mr Watt's improvements in the steam-engine. In the machines about to be mentioned, the cutters are made to advance by a train of wheels deriving their motion from the power that turas the boring-bar.
An apparatus of great merit was contrived and de. scribed in 1802 by Mr Billingsley, Engineer of the Bowling Iron-works, near Bradford. (See Repertory of Arts, second series, Vol. II. p. 322.) In this me thod, the cylinder is placed with its axis perpendi cular to the horizon. The object of which is, first, that the boring-dust may fall out, and not remain on one side of the cylinder, wearing the cutters ; so that in this way the cylinder may be bored through with out changing the cutters, by which means a more re gular bore is obtained. Secondly, That the cylinder may not deviate from its cylindrical form by its own weight, a deviation which is found to take place in large and slender cylinders when laid on their side ; the vertical diameter being then less than the hori zontal diameter.. A similar loss of shape may happen to cylinders that are improperly wedged and strap ped down for the purpose of being bored. In this method, the cylinder is fixed with screws by the flanges, where it is most capable of resistance, and the screws are disposed so as to press the cylinder equally all round. Thirdly, That the operation May be sooner completed, which is effected in con sequence of less time being employed to fix the cylinders in this method. In the usual mode of pro pelling the cutters described above, the attendance of a man is necessary to change the position of the bar on the axis of the pinion, and to raise the weight. This attendance is dispensed with in the machine under consideration, the mechanism for propelling the cutters being as follows. A leather strap passing over the boring-bar, communicates the revolving mo tion of the boring-bar to a wheel, which communi cates a slow motion by a train of wheels and pinions to an axis, bearing two pinions which work into two racks; these racks push the boring head and cutters slowly forward on the boring-bar, at the same time that the boring-head is revolving with the boring bar. The velocity with which it is required that the cutters shall advance, varies as the diameter of the cylinder varies, the moving power remaining the same. And by altering the train of wheel-work, the cutters may be made to advance with any velocity required.