Britain at Work
A Pictorial Description of Our National Industries

22ö BRITAIN AT WORK. ROUGH-TURNING A GUN-BARREL IN TURNING MACHINE. (.Photo supplied by Sir W. G. Armstrong, Whitworth & Co.] each end in order to test the quality, elasticity, and tensile strength of the steel, for if that should fail a new ingot would have to be worked. Before the hollow, rough-turned cylinder goes further, then, the steel discs cut from it are severely tested. Out of these discs there are cut several testing pieces about four inches long, with heads resembling’ short double-headed bolts, the hydraulic testing machine taking hold of the bolts at either end. The tests are made in a little office not far away, where stands a machine which does not take up much more space than a copying-press, but has tremendous power. The first duty of those conducting the tests is to note when the steel commences to move or yield as it begins to elon- gate under the stress to which it is subjected ; then a piece is elongated until a point is reached when the steel ceases to return after expansion to its original length ; and, finally, the breaking stress is ascertained by adding weight until a test piece breaks. A self-registering apparatus is attached to the bolts in the first two tests. The first test shows that the steel began to move at a pressure of 15 tons to the square inch ; the second proves that the amount of the strain which the steel will stand without per- manent set is 21 tons per square inch — in the bolt two inches long the measure of elongation is found to be just under half an inch ; and the third shows that it breaks at 36’3 tons per square inch. In the case of a big gun, say 50 tons, the minimum requirements of the Government are yielding strain 11 to 15 tons to the square inch; amount of elongation, above 15 per cent, of the length tested; and breaking strain between 27 and 35 tons per square inch. These tests refer to the steel in its soft state, as it comes from the steel works. Similar tests with other bolts follow, upon their being hardened by heat and tempered by being plunged into oil. At this last series of tests the minimum requirements for a similar gun are these: Yielding strain, 25 to 33 tons to the square inch ; amount of elongation, above 10 per cent, of the length tested ; and breaking strain, 38 to 48 tons per square inch. Assuming that the tests are satisfactory, as they were when the writer saw them, the boring of the gun is the next operation. At the first “ cut ” 9% inches are taken by a circular cutter out of the centre of the cylinder, which has an outside diameter of about 21 inches. With the barrel 30 feet long the rough boring occupies more than a week, although the machine works day and night. The borer or cutter, which is carried on the end of a substantial shaft, advances at the rate of 4^ inches per hour, that is assuming it could be kept at work con- tinuously, but, as a matter of fact, it is frequently withdrawn to admit of the examination of the bore and ensure the accuracy of the “ cut.” Although it has behind it a powerful pressure, and cuts the hardest steel like so much cheese, the bore travels silently, and with singular slowness. This slowness means economy and care. The slightest irregularity in the progress of the