Britain at Work
A Pictorial Description of Our National Industries

THE MAKING OF BIG GUNS. 227 borer over any part of the cylinder might easily mean the complete ruin of the ingot. Having been rough-bored, the barrel is toughened by being heated and tempered by being clipped in a pit of oil, operations naturally involving the use of heavy hydraulic cranes, which are all over the works. Then comes the difficult and tedious process . of “ fine-boring.” The fine-boring comprises three separate borings, and in the case of a 12-inch or 50-ton gun the rou^h “cuts ” in this stage take two or three weeks each. In the final boring from 700th to ftth of an inch, according to the gun, is left to be taken out. This operation requires the greatest care. If the bore becomes torn or damaged by the breaking of a tool or seizure of the boring head, a barrel which may now be worth between £2,000 and ^■3,000 is utterly spoiled. The barrel, having been fine-turned in the lathe on the outside, is ready to receive the outer coats of steel with which a gun is built up. A gun is really a succession of cylinders of steel shrunk over each other, and each cylinder has to be treated in almost exactly the same fashion as the barrel or central tube—that is to say, has to be tested, turned, rough- and fine-bored, and gauged carefully throughout, to ensure correctness of diameter. To attain perfect accuracy in all these borings is no easy matter, par- ticularly in the case of the central tube, for as the cutter of the bore wears down as it approaches the end of the cylinder, the diameter of the tube diminishes. The 12-inch gun consists of five cylinders or layers, or four beyond the barrel. These cylinders run in thickness thus: Barrel, 4^ in. ; second course, 5 in. ; third course, 3^ in. ; fourth course, 3^ in. ; fifth course, 4^ in. The gun is thickest over the powder chamber—about 19^ in.—because it is the seat of the explosion. In the guns made for our national service the barrel is covered from breech to muzzle with layers of wire or with long cylinders of steel, the muzzle being finished off with the old-fashioned muzzle-swell. In the older patterns of guns all the cylinders, except the inmost one, were in short lengths; the no-ton gun comprises no fewer than forty-four pieces, apart from the breech - screw and the mechanism for closing it. The number of tests which this division of the gun into forty-four sections involves is striking enough. The barrel is credited with twelve tests for each end—24 ; the other 43 pieces have four test pieces taken from each end—344. Thus the total number of tests made in the case of each separate gun is 368. The cylinders are affixed to each other by the process known as shrinkage. The bore of the cylinders (apart from the original WIRING A BIG GUN. {Photo supplied by Sir W. G. Armstrong, Whitworth & Co.)