Boring of ORDNANCE. Till within these 20 years, iron ordnance were cast with a cylindrical cavity, nearly of the dimension of the caliber of the piece, which was afterwards enlarged to the proper caliber by means of steel-cutters fixed into the dog-head of a boring-bar-iron. Three side-cutters equidistant were requisite to preserve the caliber straight and cylindrical; and a single cutter was used at the end of the bar to smooth the breech of the piece. In boring ordnance cast hollow, the piece was fixed upon a carriage that could be moved backwards and forwards in a direct line with the centre of a water-wheel; in this centre was fixed the boring-bar, of a sufficient length to reach up to the
breech of the piece, or more properly to the furthest end of the caliber. The carriage with the piece being drawn backwards from the centre of the water-wheel to introduce the boring and finishing bars and cutters, it is then pressed forwards upon this bar by means of levers, weights, &c. and the water-wheel being set going, the bar and fullers are turned round, and clean out and smooth the caliber to its proper dimensions.
Experience at last pointed out many inconveniences arising from the method of casting guns hollow, and widening the calibers by these boring bars. For the body of iron of the hollow-gun, being, at casting, in contact with the core that made the caliber within-side, and with the mould without-side, began to consolidate towards these sides in the first place, sooner than in the intermediate space, where of course the contraction of the iron takes place; by which means, all guns cast hollow become more or less spongy where they ought to have been most compact; and numberless cavities also were created round the cores, from stagnated air generated in them, which were too deep to be cut out by the boring.
To remedy these defects, iron ordnance is now universally cast solid, by which means the column of iron is greatly enlarged, and the grain more compressed; and the contraction of the iron becomes in the heart of the column, and consequently is cut out by the perforation for the caliber.
Guns are bored out of the solid reversely from the hollow method. The piece A is placed upon two standards BB, by means of two journeys, turned round by the water-wheel C, the breech D being introduced into the centre of the wheel, with the muzzle towards the sliding carriage E, which is pressed forwards by a ratch F, and weights, in the same way as the gun-carriage was in hollow-boring. Upon this sliding carriage is fixed, truly horizontal and centrical to the gun, the drill-bar G, to the end of which is fixed a carp's tongue drill or cutter H; which, being pressed forward upon the piece whilst it is turning round, performs the bore, which is afterwards finished with boxes and cutters as the hollow guns were. The principal difficulty of perforating solid guns truly centrical, arises from the contraction of the iron above-mentioned; which, resisting the drill unequally, tends to throw it out of the centrical line.