From "Nature" A weekly journal of illustrated science volume 47, november 1892 through April 1893.
THE MAKING OF RIFLES.
A T a recent meeting of the Institution of Civil Engineers, Mr. •**• John Rigby, superintendent, Enfield Factory, read an interesting paper on the manufacture of small .mn .. We reproduce from the abstract printed for the Institution Mr. Kigby's lucid account of the various processes of manufacture of the components of the Lee-Metford Mark I. magazine-rifle, of 0-303 inch bore, the weapon adopted for the British Army—an account which he prefaced with a general description of the Enfield Factory.
The most important part of a rifle was the barrel, which had always engaged the special attention of gun-makers. Up to the time of the Crimean War, it was, for the bulk of British troops, a comparatively rude tube of iron, lap-welded under rolls and tapering externally, with a cylindrical bore of about ä inch diameter. The barrel of the present day was a steel tube of accurate workmanship, only -fc inch bore, almost perfectly true and straight, rifled to ^Vir inch, and so closely inspected that the existence of the most minute grey or seam in the bore, requiring a highly-practised eye to detect it, was sufficient to condemn it. The material used was produced either by the Siemens-Martin or the crucible process of manufacture, and was supplied to Enfield as a solid round bar l| inch diameter and 15^ inches long. After severe testing, this bar was parsed through a rolling-mill to draw it to its full length : it was then taken to the forge, the swell at the breech-end was stamped to the required shape by a steamhammer, and afterwards straightened cold. The next step was to submit the bar, without annealing, to the turning and drilling-machines. The latter were horizontal, the drills operating from each end. In the process of drilling, the barrel revolved at nearly 1,000 revolutions a minute against half-round bits held flat down, a capillary tube, of brass, supplying a soap-and-oil emulsion, at a pressure of 8o Ib. to the square inch, to wash out theswarth and cool the cutting-edge. The drills advancing from each end continued boring until a small disk about TJ7 inch diameter broke out, and the two holes met. The tendency of the drills to follow the line of axis of a revolving bar was one of those curious occurrences in practical mechanics which might be accounted for after observation, but which no one would predict. Occasionally, through some defect in the steel, a drill wandered from the axial line ; in this case the barrel was taken from the machine and reset sufficiently to bring the hole true again. To test its truth, a ray of light was made to illuminate the flat bottom of the hole while the barrel slowly revolved. It was very rarely that a barrel was rendered waste from bad drilling. Rough-boring followed with a three-edged bit, the blade being about 4 inches long. The rough external turning was effected in self-acting lathes, which gave the required curved taper. Three or four cutters acted simultaneously, each producing a long cutting that attested the quality of the metal of the barrel. The operation of barrel-setting followed. Previous to rough-turning, the barrels were fairly straight internally, but the removal of the metal caused slight inequalities which were tested by the eye of the barrel-setter, and corrected by transverse blows. This constituted skilled labour of a peculiar character, and was performed by young men of good sight, who were specially trained for the purpose. After middle life the eye generally lost some of the quality necessary for this work, and it was rare to find a man excel in it after that period. Many mechanical devices had been contrived to supersede the simple ray of light laid, as ¡fit were a straight edge, along the surface of the bore ; but the eye still remained the arbiter of straightness and could be relied on for very accurate results. The construction of the barrel was completed by the important operation of rifling. In British small-arm factories the system was followed of planing out each groove separately with a hooked Gutter, and had been brought almost to perfection. In Continental and American factories the grooves were ploughed out by cutters, with several cut I ing or knife-edges set at an angle and following one another in the manner of a single-cut file or float. Similar machines had been tried at Enfield, but did not give as smooth a cut as the slower-moving, single-tooth machines. A few passes of a lead lap, fed with fine emery, removed any burr that might remain, and completed the polish ; a cylindrical lap, spinning rapidly, was then passed through, and gave the final finish to the barrels. The limits of gauging were from 0-303 too'305 inch.
Next in importance to the barrel was the mechanism of the breech, for which the material preferred was crucible cast-steel
of a mild character, but capable of being hardened in those parts exposed to the pressure of the bolt. The body was forged in two operations under the steam-hammer ; it was then drilled and subjected to along series of operations, in the course of which the end was recessed to receive the screwed end of the barrel, and the corresponding thread in the recess was milled out in a specially-contrived machine, which insured that the thread should always start in the same place relative to the gauged part of the body, a point of great importance. The bolt, also of crucible cast-steel, was forged under the steam-hammer. A special machine, invented at Enfield, was used to finish the bolt after shaping. After machining, the bolts, packed in wood charcoal in iron cases, were heated and hardened by immersion in I oil. The temper of the handle was then reduced in a lead bath. The rest of the bolt was tempered straw-colour. The bolt-head was similarly hardened and tempered.
The other components of a complete rifle were mostly shaped by mills built up to the proposed profile, or by copy-milling machines. The process of drifting was used with good results I at Enfield. AH such slots or perforations as had parallel sides, and were not cylindrical, were so finished. The common practice in drifting was to push the drift, but at Enfield much better work was accomplished by pulling. It was found that used in this way drifts were very valuable for interchangeable work. The sides were cut with successive teeth, each slightly larger than the preceding one, andfthe whole length of the drift was drawn through. Emery wheels were also largely used at Enfield as a substitute for finish-milling and filing. The wheels ran under hoods connected with a pneumatic exhaust that carried away the heated particles of steel and grit. It was popularly supposed that a machine once adjusted to turn out a component of a certain size and shape was capable of reproducing such in large numbers, all absolutely identical. This was so far from being the case that no die, no drill, and no milling-cutter actually made two consecutive articles the same size. The wear of the cutters or dies proceeded slowly but surely, and it was only possible to produce in large numbers components of dimensions varying betweenja superior and an inferior limit. In smallarm manufacture a variation of about one two thousandth of an inch was about the amount tolerated, but it varied according to the size of the piece. A difference of diameter of one twothousandth of an inch in the sight axis-hole, and in the size of the pin or axis, would cause a serious misfit, whereas a similar difference in the measurement of the magazine, or of ihe recess in which it lay, would be quite immaterial. The operations of gauging, proving the bairel, and sighting, were successively described, as al-o the manufacture of the stock, which was of the wood known as Italian walnut, though largely grown in other countries. Among the smaller components, the screws were mentioned as being rapidly produced by the automatic screwmaking machines of Pratt and Whitney.
The Component Store received the various finished parts, which numbered 1591, or, including accessories, 1863, and issued them to tne foreman of the assembling-shop. Theoretically, the assemblers should have nothing to do but to fit and screw them together, but in practice small adjustments were found necessary. The amount of correction was generally exceedingly small, and was done wherever possible with the aid of emery wheels. The completed arms were submitted to inspection, and then issued in cases of twenty each to the Weedon Government Store or elsewhere.
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