FINISHING OPERATIONS. – BORING
From the Middle Water Shops, where this welding is done, the barrels are conveyed to the Upper Shops, where the operations of turning, boring and grinding are performed. Of course the barrel when first welded is left much larger in its outer circumference, and smaller in its bore, than it is intended to be when finished, in order to allow for the loss of metal in the various finishing operations. When it comes from the welder the barrel weighs over seven pounds: when completely finished it weighs but about four and a half pounds, so that nearly one half of the metal originally used, is cut away by the subsequent processes.
The first of these processes is the boring out of the interior. The boring is performed in certain machines called boring banks. They consist of square and very solid frames of iron, in which, as in a bed, the barrel is fixed, and there is bored out by a succession of operations performed by means of certain tools which are called augers, though they bear very little resemblance to the carpenter's instrument so named. These augers are short square bars of steel, highly polished, and sharp at the edges – and placed at the ends of long iron rods, so that they may pass entirely through the barrel to be bored by them, from end to end. The boring parts of these instruments, though they are in appearance only plain bars of steel with straight and parallel sides, are really somewhat smaller at the outer than at the inner end, so that, speaking mathematically, they are truncated pyramids, of four sides, though differing very slightly in the diameters of the lower and upper sections.
The barrels being fixed in the boring bank, as above described, the end of the shank of the auger is inserted into the centre of a wheel placed at one end of the bank, where, by means of machinery, a slow rotary motion is given to the auger, and a still slower progressive motion at the same time. By this means the auger gradually enters the hollow of the barrel, boring its way, or rather enlarging its way by its boring, as it advances. After it has passed through it is withdrawn, and another auger, a very little larger than the first is substituted in its place; and thus the calibre of the barrel is gradually enlarged, almost to the required dimensions.
Almost, but not quite; for in the course of the various operations which are subsequent to the boring, the form of the interior of the work is liable to be slightly disturbed, and this makes it necessary to reserve a portion of the surplus metal within, for a final operation. In fact the borings to which the barrel are subject, alternate in more instances than one with other operations, the whole forming a system far too nice and complicated to be described fully within the limits to which we are necessarily confined in such an article as this. It is a general principle however that the inside work is kept always in advance of the outside, as it is the custom with all machinists and turners to adopt the rule that is so indispensable and excellent in morals, namely, to make all right first within, and then to attend to the exterior. Thus in the case of the musket barrel the bore is first made correct. Then the outer surface of the work is turned and ground down to a correspondence with it. The reverse of this process, that is first shaping the outside of it, and then boring it out within, so as to make the inner and outer surfaces to correspond, and the metal every where to be of equal thickness, would be all but impossible.
TURNING
After the boring, then, of the barrel, comes the turning of the outside of it. The piece is supported in the lathe by means of mandrels inserted into the two ends of it, and there it slowly revolves, bringing all parts of its surface successively under the action of a tool fixed firmly in the right position for cutting the work to its proper form. Of course the barrel has a slow progressive as well as rotary motion during this process, and the tool itself, with the rest in which it is firmly screwed, advances or recedes very regularly and gradually, in respect to the work, as the process goes on, in order to form the proper taper of the barrel in proceeding from the breech to the muzzle. The main work however in this turning process is performed by the rotation of the barrel. The workman thus treats his material and his tools with strict impartiality. In the boring, the piece remains at rest, and the tool does its work by revolving. In the turning, on the other hand, the piece must take its part in active duty, being required to revolve against the tool, while the tool itself remains fixed in its position in the rest.
Among the readers of this article there will probably be many thousands who have never had the opportunity to witness the process of turning or boring iron, and to them it may seem surprising that any tool can be made with an edge sufficiently enduring to stand in such a service. And it is indeed true that a cutting edge destined to maintain itself against iron must be of very excellent temper, and moreover it must have a peculiar construction and form, such that when set in its proper position for service, the cutting part shall be well supported, so to speak, in entering the metal, by the mass of the steel behind it. It is necessary, too, to keep the work cool by a small stream of water constantly falling upon the point of action. The piece to be turned, moreover, when of iron, must revolve very slowly; the process will not go on successfully at a rapid rate; though in the case of wood the higher the speed at which the machinery works, within certain limits, the more perfect the operation. In all these points the process of turning iron requires a very nice adjustment; but when the conditions necessary to success are all properly fulfilled, the work goes on in the most perfect manner, and the observer who is unaccustomed to witness the process is surprised to see the curling and continuous shaving of iron issuing from the point where the tool is applied, being cut out there as smoothly and apparently as easily as if the material were lead.
THE STRAIGHTENING
One of the most interesting and curious parts of the process of the manufacture of the barrel, is the straightening of it. We ought, perhaps, rather to say the straightenings, for it is found necessary that the operation should be several times performed. For example, the barrel must be straightened before it is turned, and then, inasmuch as in the process of turning it generally gets more or less sprung, it must be straightened again afterward. In fact, every important operation performed upon the barrel is likely to cause some deflection in it, which requires to be subsequently corrected, so that the process must be repeated several times. The actual work of straightening, that is the mechanical act that is performed, is very simple – consisting as it does of merely striking a blow. The whole difficulty lies in determining when and where the correction is required. In other words, the making straight is very easily and quickly done; the thing attended with difficulty is to find out when and where the work is crooked; for the deflections which it is thus required to remedy, are so extremely slight, that all ordinary modes of examination would fail wholly to detect them; while yet they are sufficiently great to disturb very essentially the range and direction of the ball which should issue from the barrel, affected by them.
The above engraving represents the workman in the act of examining the interior of a barrel with a view to ascertaining whether it be straight. On the floor, in the direction toward which the barrel is pointed, is a small mirror, in which the workman sees, through the tube, a reflection of a certain pane of glass in the window. The pane in question is marked by a diagonal line, which may be seen upon it, in the view, passing from one corner to the other. This diagonal line now is reflected by the mirror into the bore of the barrel, and then it is reflected again to the eye of the observer; for the surface of the iron on the inside of the barrel is left in a most brilliantly polished condition, by the boring and the operations connected therewith. Now the workman, in some mysterious way or other, detects the slightest deviation from straightness in the barrel, by the appearance which this reflection presents to his eye, as he looks through the bore in the manner represented in the drawing. He is always ready to explain very politely to his visitor exactly how this is done, and to allow the lady to look through the tube and see for herself. All that she is able to see, however, in such cases is a very resplendent congeries of concentric rings, forming a spectacle of very dazzling brilliancy, which pleases and delights her, though the mystery of the reflected line generally remains as profound a mystery after the observation as before. This is, in fact, the result which might have