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drill, or bow, might therefore be expressed by pumps, whose diameter is small, are fixed within this term; but it has been more particulary ap- iron rings, by means of screws, in the same plied of late to the action of those machines manner as described below in Mr. Murray's apwhich have been invented for finishing the cy- paratus. The rings are made accurately cylindrilinders of steam-engines, blowing-machines, cal by turning, as is also the boring-bar. The pump-barrels, &c., and for boring the earth. boring-bar has four cross arms on its outer ex

For Boring of Cannon, see CANNON. tremity, to one of which a handle is fixed, whereby

Boring of CYLINDERS for steam-engines, a workman makes the boring-bar revolve. The blowing-machines, the barrels of large pumps, cutter-head is made to advance along the boring&c. is generally performed by steel-cutters, which bar by a screw. See Repertory of Arts, Vol. XIII. describe a cylindrical course on the inside sur- In 1802 Mr. Billingsley, of the Bowling Ironface of the cylinder already cast, while it re- works, near Bradford, constructed an apparatus mains fixed. Steam-engine cylinders were first in which the boring is performed perpendicularly. made of brass, or copper and tin mixed; but See Repertory of Arts, second series, Vol. II. cast-iron has of late become the universal ma- p. 322. One object is, that the boring-dust may terial. The cutters are fixed in what is called fall out, and not remain on one side of the cylinder, the cutter-head, which turns with the boring bar, wearing the cutters; and in this way the cylinder while it is impelled round the interior surface of may be bored through without changing the cutthe cylinder by a rack, with a pinion moved by ters. Another advantage proposed is, that the a lever and weight. A hollow tube of cast-iron cylinder may be made more true, and not deviate is generally the axis or boring-bar employed, from its cylindrical form by its own weight, a having a groove through it, the length of which circumstance which is found to take place in is proportioned to the length of the cylinder. large and slender cylinders when laid on their The cutter-head is composed of two cast-iron side. In this method the cylinder is fixed with rings, the first of which is accurately fitted on screws by the flanges, where it is most capable the bar, which is made truly cylindrical, so that of resistance, and the screws are disposed so as this ring may slide along it; the second ring is to press the cylinder equally all round. The fixed round the first by wedges; and on its cir- operation, it is also contended, may be thus cumference are eight notches to receive the steel- sooner performed, in consequence of less time cutters, also fixed in by wedges. The first ring being required to fix the cylinders, and no atis fixed on the bar, so as to make the whole tendance being necessary to change the position cutter-head move round with it by means of two of the bar on the axis of the pinion. The smaller bars, which go through notches in that mechanism for propelling the cutiers is as folring, and pass through the groove of the boring- lows :—A leather strap passing over the boringbar. These small bars have each a round hole bar, communicates the revolving motion of the in the part which passes through the geometrical boring-bar to a wheel, which gives a slow motion axis of the boring-bar ; through these holes there by a train of wheels and pinions to an axis, passes a bolt, which forms the end of the rack; bearing two pinions which work into two racks; a key is put through the end of the bolt, which these racks push the boriog-head and cutters prevents the rack from being drawn back by the slowly forward on the boring-bar, at the same lever and weight; and by this means the rack, time that the

boring-head is revolving with the impelled by the lever and weight, pushes forward boring-bar. The velocity with which it is rethe cutter-head, which is at the same time re- quired that the cutters shall advance, varies as volving with the boring-bar: the connexion of the diameter of the cylinder varies, the moving the rack and cutter-head being round, and in the power remaining the same; and, by altering the axis of motion, the rack is thereby free from the train of wheel-work, the cutters may be made to circular motion of the cutter-head. This boring- advance with any given velocity. bar was invented in the works of Mr. Wilkinson, Our plate Boring, figs. 1, 2, 3, and 4, exat the time when accurately bored cylinders hibits different views of a machine for boring came to be required in consequence of Mr. cylinders, invented 'by Mr. Murray of Leeds. Watt's improvements in the steam-engine. In Fig. 1 is an elevation, and fig. 2 a plan, of the the following machines the cutters advance by a machine. W, fig. 1 and 2, is the spur wheel, train of wheels deriving their motion from the deriving its motion from water or steam, and power that turns the boring-bar.

communicating a revolving motion to the boringA patent was granted in 1799 to Mr. Mur- bar. The toothed wheel x, fig. 1, moves round doch of Redruth for an improved method of with the boring bar, B. on which it is fixed; it constructing steam-engines. He proposes to gives motion through the wheels D and E, and employ an endless screw for boring, turned by to the screw S, whose threads act on the two the moving power; this screw to work into a racks, which racks are fixed to the cutter-head toothed wheel, whose axis carries the cutter-head. H, and revolve with it. The volocity with which This method, he says, produces a more smooth the cutter-head is impelled along the cylinder, and steady motion than the usual mode of fixing depends upon the number of threads of the the boring-bar immediately on the axis turned by screw in a given length, and on the proportions the moving power. Mr. Murdoch forms the of the wheels A, C, D, and E, to each other. cylinder and steam-case by casting them of one By varying the velocity of the screw, the cuttersolid piece, and then boring a cylindrical inter- head may be made to move in either direction, stice, by means of a tool made of a hollow cy- up or down the cylinder. F is a pinion, whose linder of iron, with steel-cutters fixed to its edge, axis ends in a square, which may be wrought by and acting like a trepan. The chambers of brass a key so as to bring the cutter-head out of the

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