Page images
PDF
EPUB

drill, or bow, might therefore be expressed by this term; but it has been more particulary applied of late to the action of those machines which have been invented for finishing the cylinders of steam-engines, blowing-machines, pump-barrels, &c., and for boring the earth.

For BORING OF CANNON, see CANNON. BORING OF CYLINDERS for steam-engines, blowing-machines, the barrels of large pumps, &c. is generally performed by steel-cutters, which describe a cylindrical course on the inside surface of the cylinder already cast, while it remains fixed. Steam-engine cylinders were first made of brass, or copper and tin mixed; but cast-iron has of late become the universal material. The cutters are fixed in what is called the cutter-head, which turns with the boring bar, while it is impelled round the interior surface of the cylinder by a rack, with a pinion moved by a lever and weight. A hollow tube of cast-iron is generally the axis or boring-bar employed, having a groove through it, the length of which is proportioned to the length of the cylinder. The cutter-head is composed of two cast-iron rings, the first of which is accurately fitted on the bar, which is made truly cylindrical, so that this ring may slide along it; the second ring is fixed round the first by wedges; and on its circumference are eight notches to receive the steelcutters, also fixed in by wedges. The first ring is fixed on the bar, so as to make the whole cutter-head move round with it by means of two smaller bars, which go through notches in that ring, and pass through the groove of the boringbar. These small bars have each a round hole in the part which passes through the geometrical axis of the boring-bar; through these holes there passes 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 connexion of the rack and cutter-head being round, and in the axis of motion, the rack is thereby free from the circular motion of the cutter-head. This boringbar 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 following machines the cutters advance by a train of wheels deriving their motion from the power that turns the boring-bar.

A patent was granted in 1799 to Mr. Murdoch of Redruth for an improved method of constructing steam-engines. He proposes to employ an endless screw for boring, turned by the moving power; this screw to work into a toothed wheel, whose axis carries the cutter-head. This method, he says, produces a more smooth and steady motion than the usual mode of fixing the boring-bar immediately on the axis turned by the moving power. Mr. Murdoch forms the cylinder and steam-case by casting them of one solid piece, and then boring a cylindrical interstice, by means of a tool made of a hollow cylinder of iron, with steel-cutters fixed to its edge, and acting like a trepan. The chambers of brass

pumps, whose diameter is small, are fixed within iron rings, by means of screws, in the same manner as described below in Mr. Murray's apparatus. The rings are made accurately cylindri cal by turning, as is also the boring-bar. The boring-bar has four cross arms on its outer extremity, to one of which a handle is fixed, whereby a workman makes the boring-bar revolve. The cutter-head is made to advance along the boringbar by a screw. See Repertory of Arts, Vol. XIII.

In 1802 Mr. Billingsley, of the Bowling Ironworks, near Bradford, constructed an apparatus in which the boring is performed perpendicularly. See Repertory of Arts, second series, Vol. II. p. 322. One object is, that the boring-dust may fall out, and not remain on one side of the cylinder, wearing the cutters; and in this way the cylinder may be bored through without changing the cutters. Another advantage proposed is, that the cylinder may be made more true, and not deviate from its cylindrical form by its own weight, a circumstance which is found to take place in large and slender cylinders when laid on their side. 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. The operation, it is also contended, may be thus sooner performed, in consequence of less time being required to fix the cylinders, and no attendance being necessary to change the position of the bar on the axis of the pinion. The mechanism for propelling the cutters is as follows:-A leather strap passing over the boringbar, communicates the revolving motion of the boring-bar to a wheel, which gives 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 given velocity.

Our plate BORING, figs. 1, 2, 3, and 4, exhibits different views of a machine for boring cylinders, invented 'by Mr. Murray of Leeds. Fig. 1 is an elevation, and fig. 2 a plan, of the machine. W, fig. 1 and 2, is the spur wheel, deriving its motion from water or steam, and communicating a revolving motion to the boringbar. The toothed wheel Ă, fig. 1, moves round with the boring bar, B. on which it is fixed; it gives motion through the wheels D and E, and to the screw S, whose threads act on the two racks, which racks are fixed to the cutter-head H, and revolve with it. The volocity with which the cutter-head is impelled along the cylinder, depends upon the number of threads of the screw in a given length, and on the proportions of the wheels A, C, D, and E, to each other. By varying the velocity of the screw, the cutterhead may be made to move in either direction, up or down the cylinder. F is a pinion, whose axis ends in a square, which may be wrought by a key so as to bring the cutter-head out of the

[graphic]

Page 332 Vol 4

BORING.

London Published by Thomas Tegg. 73.Cheapside December 11826.

[merged small][merged small][merged small][graphic][merged small][merged small][subsumed][subsumed][subsumed][merged small][subsumed][subsumed][subsumed][merged small][subsumed][merged small][merged small]
[merged small][ocr errors][merged small][merged small]
[ocr errors]
« PreviousContinue »