BORING, generally speaking, is the Art of per forating a solid body. In the present article, we propose to give some account of the Boring of CAN NON, of CYLINDERS Of MUSKETS, of PORTLAND STONE, of ROCKS, and of WOODEN PIPES.
I. Boring of CANNON is performed by placing the cannon on an axis which is turned by a very strong power, whilst a steel cutter, in form of a drill, is pressed against the metal, and excavates the cy lindrical cavity which is required. Boring may be considered as a branch of the art of turning; which, in general, is the formation of cones, cylinders, and other figures that have an axis, by making a straight line or curve revolve round the axis on which the material is fixed, or by making the material revolve whilst the generating line remains at rest. In turn ing bodies of no great degree of hardness, and where it is required to take off only a small portion of the surface at once, a small power is sufficient to put the turning machine in motion ; and the longer the edge of the cutter which is applied to the metal is, and the harder the metal, the greater force is requires to turn the machine.
Cannon, at first, were frequently made of bars of malleable iron, placed longitudinally, and these bars covered with iron hoops, the whole welded or brazed together. Ordnance of this construction was not sufficiently strong to resist the explosion of the pow der, and did not admit of the cylindrical cavity be ing formed with much accuracy. Its use was, there fore, gradually laid aside, and guns of cast metal were employed. And before the casting of cannon became general, guns of cast metal were reserved for the most important situations; thus the ships of the Admiral and Vice-Admiral alone had cast-metal cannon; the other ships of war being armed with wrought-iron guns only.
Copper, without mixture, has been employed to cast guns, as appears from two large cannon made in the time of Henry VIII. and bearing his name, in the armoury of the Tower of London. But the only two materials now used for cannon are bronze, which is a mixture of copper and tin, pnd cast-iron.
In modern times, the use of cast-iron cannon has be come more general, as that metal has the advantage of not being softened by the heat of the inflanuna • tion of the powder ; whereas brass guns, when fired many times in rapid succession, become heated so nearly to the melting temperature of the metal, that the 'muzzle of the gun droops.
The first cannon made of cast-metal were cast hollow, with a cavity as nearly cylindrical as could be executed by casting. The surface of this cavity • was then smoothed on a boring machine by steel cutters set in a copper head, and disposed so as to describe a cylinder terminated by a half sphe soid. These cutters (in French alizoirs, and the ope ration alizer) are represented in the French Encyclope aie—Planches--Fonte. This method of making guns has been long laid aside on account of the holes and inequalities in the cavity thus formed, and the diffi culty of casting the cavity so as that its axis shall coincide with the axis of the piece. Cannon are now always cast solid, and the cylindrical cavity is formed by boring in this solid mass.
The power employed for boring cannon ought to be in proportion to the hardness of the metal of which they are composed, and to the size of the pieces. For the boring of guns of brass, as it is called, that is, 4 metal composed of ten parts of copper, ode of tin, and two of brass, or of these metals in other proportions, a metal softer and more easily bored than cast-iron, horses are fre quently employed as a moving power ; but the strong moving powers of water or steam must be had recourse to for boring large guns of cast iron, which is the material used for making the largest guns now in use, and is also the hardest substance used in their manufacture. Indeed, some kinds of cast-iron are too hard to admit the action of the borer ; and for the making of 4uns it is necessary to melt pig-iron of different qualities together, in or der to have a metal that shall possess no more than the required degree•f hardnese.