156 MACHINE TOOLS FIG. 9. Drills. (within certain limits as to distance from the edge, ttc.), the first by adjusting the work below the drill, the second by adjusting the drill over the work. A wall drill dis penses with a table altogether, and gives great facilities for operating on large pieces of work, especially if the means of adjustment is secured by the radial arm just men tioned. Multiple drilling machines, with which a series of holes can be drilled at once, are serviceable tools for some purposes , mainly on account of the sav ing of time which they effect. Three drills are shown in fig. 9, the first the old, bad, but not yet quite superseded pattern, which is incapable of making a straight or clean hole of any consider able depth, and which loses its ori ginal diameter both in wear and in sharpening ; the second the tu ist drill, which compares favourably with it in every one of these respects ; and the -third a pin drill, for enlarging a hole already existing. Boring machines deal chiefly with apertures of large diameter, for which great straightness and accuracy are required, such as the cylinders of pumps, steam-engines, &c., or the bores of guns. The latter object brought them very early into existence, as already mentioned, and the general principle upon which the rude machinery of more than a century ago bored out the old cast iron mortars is still used for the powerful weapons of our own day. It consists in the employment of a boring bar formed by mounting a series of cutters (or a combination of guides and cutters) round the periphery of a cylindrical " head " somewhat less in diameter than the required bore. Fig. 10 will render evident the great similarity which exists between the oldest and the most re cent gun-boring heads, the one be ing taken from the Encyclopedic already referred to, and the other from a draw ing of a boring-bar used for a similar purpose at Woolwich, The head may be either a fixture at the end of its bar, in which case it forms a kind of drill with several cutting edges, or it may be so arranged as to traverse the bar to a small extent at each revolution, a plan which is generally preferred for all open-ended cylinders, &c., and which admits of the work being kept stationary throughout the operation. The bar when in use is mounted either vertically or hori zontally, according to circumstances, in a lathe or boring machine. The excellent results obtainable in this manner will be appreciated from the fact that with the gun-boring machinery at Woolwich a hole 10 inches in diameter and 10 feet deep can be bored in solid steel at a single operation, and holes have been carried to a depth of 24 feet with a variation of less than T i^ of an inch in the diameter. The accuracy of modern machine work indeed not unfrequently brings into prominence sources of error which were previously unsuspected. The boring of large cast iron cylinders affords an instance of this, for it has been found that, however true the boring tool may be, the distortion of the cylinder itself, through being laid on its side, is sufficient to mar the results obtained with it ; consequently it has been found necessary always to bore a large cylinder in the vertical position which it will occupy when in use. In the construction of modern machinery, &c., it is often neces sary to depart from the simple geometric forms to the production of which the tools which have thus far occupied our attention are mainly adapted. Ve will now glance at some of the labour-saving contrivances applicable to other cases. The slot-drilling rn.ac.lunc effects (liy a method said to have been FIG. 10. Gun-Boring Heads. FIG. 11. Slot Drillinf FIG. 12. Slotting Machine, circular movement can thus be given first used about the year 1848) the conversion of the circular cavity producible with an ordinary drilling machine into an elongated "slot " or slit. The extent of the elongation can be varied by in creasing or diminishing the re ciprocating movement of the slide which carries the rotating drill. An example of it is given in lig. 11, and the cutting end of a roughing drill is shown to an enlarged scale. Where smooth ness of the sunken surface is re quired this is followed by a rose or some other finishing tool. The slotting machine (fig. 12) also cuts grooves and slots, but in an entirely different manner. Those who are acquainted with the wood mortising ma chine, from which the idea of this tool was derived by Roberts of Manchester, will at once understand its prin ciple, and will appre ciate the good service which can be rendered by this powerful paring tool. A large propor tion of the shaping, &c., required in heavy work is now done in these machines, which are sometimes of great size and power. The table on which the work is placedispivoted and mounted on a com pound slide, and a self- acting horizontal transverse or to it. For work of moderate size shaping machines, which are more of recent introduction than either slotting or planing machines, both of which they resemble in their action, are in some respects more convenient. The slide which carries the tool is in their case hori zontal, and its short but variable strokes are in a direction trans verse to the bed, along which it can travel, just as a slide-rest travels along a lathe bed. Curved surfaces, either convex or concave, as well as flat ones, can generally be worked iqi automatically in these machines, one of which is shown in fig. 13, but their details *_."-. and arrangements vaiy consider- ably. For operating upon small FJG _ 13i _ shapiug Machill( .. surfaces, especially those of com plicated outline, the plan of employing a revolving cutter, re sembling a circular file, is now gaining favour. It i.s interesting to note that this is but a return to a system which is stated to have been devised by Dr llooke in 1664, and which was certainly used in some of the early "engines" for cutting the teeth of wheels. One such cutter or mill ing tool is shown in lig. 14. Others are of a plain cylindrical form, or are varied in outline to any extent to suit the particular purpose for which they are intended, amongst which purposes may be mentioned that of cutting the teeth of other milling tools. When mounted on a compound slide and used in a milling machine, a tool of this kind is a labour-saving contrivance of a very efficient kind, and it should be observed that it may in some cases be employed for finishing metal surface! possessing a double curvature, to which none of the foregoing planing or shaping machines could be applied. Profiling or edge-milling machines are a still more recent appli cation of the milling-tool system. They enable the curved or com plicated outline of a previously prepared templet to be reproduced with certainty any number of times in succession. They are in fact copying machines, acting in a similar manner to Jordan s carving machine or Blanchard s copying lathe, in both of which the form of the copy is derived from the original pattern by causing this pattern to control the movements of the revolving tool. Another class of machine tools, which has sprung up of late years and is rapidly extending, is that of emery grinders. One thing FIG. 14.
Milling Tool.