MACHINE TOOLS 153 arranged sawing, mortising, shaping, and other machines by which this was accomplished we cannot enter, but they are of great interest, not only from their intrinsic merits, but also as being, if not the very first, certainly superior to any which had previously been used. Our limited space, however, will be more profitably devoted to giving a few examples of the general tools used in engineers work shops. The Steam-Hammer, which in some respects may be re garded as the most important of machine tools, has already been noticed (see HAMMER, vol. xi. p. 425). Second only to it in importance, and long anterior to it in date, stands the lathe. At what exact point of its development from the simple foot lathe it first became entitled to rank as a machine tool we will not stop to inquire, for the origin of this, as of most of the mechanical legacies which have been handed down to us by successive inventors and improvers, is involved in much obscurity. But as far as tools laying any claim to precision are concerned it appears certainly to have been the first to come into existence. On the Con tinent, mechanism to be used in conjunction with it for oval turning, and for producing mouldings oblique to the axis of the work, had been devised as early as 1569, in which year one Jacques Besson published drawings of two lathes so arranged. Whether much additional beauty was obtained by thus departing from the circular sections pro ducible with the simple lathe, and converting them into distorted ones, such as that sketched in fig. 1 (reduced from Besson), may perhaps be questioned, but the taste for this FiG - 1. Swash Work, "swash" work, as it is called, ere long extended also to England. Moxon, the first English writer on the subject, gives a drawing of a very similar lathe, and he men tions the name of an established London maker whose oval engines and swash engines, and all other engines, were " excellently well made," so they were apparently in some demand at the time of his writing (1680). Screw cutting in the lathe was another problem and a more worthy one -which occupied the attention of inventors at the same early period. A curious but mechanically very imperfect arrangement for accomplish ing it (with which, however, threads either right or left handed could be cut on tapered and oval as well as on cylindrical work) is given in another of Besson s engrav ings. In this the tool is entirely supported and its movements are controlled by the machine instead of being held in the hand, an arrangement of which the great advantage appears to have been but tardily appreciated, though it contains the germ of the principle which, applied first in the slide-rest of the lathe, and subsequently in machine tools of almost every typs, has enabled tasks of constantly increasing severity to be successfully dealt with. Nearly two centuries seem to have elapsed before what we now know as the slide-rest became a recognized adjunct to the turning lathe, though in the meantime arrangements had been devised for controlling the motion of the tool by attaching it to some portion of the mechanism in some special cases, as in that of two curious lathes for turning hyperbolic, spherical, or plane mirrors for optical purposes, of which engravings were published at Home in 1648. Its first definite appearance in print occurs in the great French Encyclopedic, published in 1772. Detail drawings of an admirable slide-rest are given in one, and evidence of its being then in regular use occurs in several of the very interesting engravings of that ponderous work, which gives so clear an insight into the methods then employed in France in the various crafts. The description, however, by no means settles the question of its origin. It is pretty certain that the slide-rest was reinvented in England by the ingenious Henry Maudslay, when he was employed in Mr Bramah s workshop in London, where " Maudslay s go-cart" (as it was at one time derisively called) was first set to work in 1794. That he had not previously seen the drawings just mentioned cannot of course be proved, but the high price at which the Encyclopedic was published makes it very probable that no copy of it had at that time come under the notice of a hard working English mechanic. The intrinsic differences of the two slide-rests tend towards a similar conclusion. Who ever may have been its first inventor, the slide-rest has cer tainly proved itself to be the most invaluable of all the additions made to the turning lathe. Its indispensability to the modern power-lathe will be readily appreciated from the following examples. An engraving of a simple slide-rest for use with a foot lathe has already been given (see LATHE), and its effect in reducing the labour of the turner was then pointed out, The self-acting slide-rest (fig. 2) carries this reduction slill farther ; and, by deriving from the lathe itself the small " feed " movement ne cessary for bringing the tool to bear on succes sive portions of tlife work, it dispenses wholly with the need for physical exertion on the part of the work man, and does not even demand his con tinuous supervision. One result of this is that the slide lathe (for so complete is the union between the slide-rest and the lathe that they must now be re garded as one machine) affords a complete solution of the screw-cutting problem, since, by varying the extent to which the rest traverses the lathe bed during each revolu tion of the mandrel, a screw thread of any desired pitch can be cut with a single tool. In fig. 3, which shows a self-acting screw-cutting lathe with double-geared headstock, of a type now well estab lished, the arrangements for obtaining and varying this traversing motion may be observed. A steel leading screw FIG. 2. Self- Acting Slide-Best. FIG. 3. Self- Acting Screw-Cutting Lathe. runs along the front of the lathe bed, and with it the slide- rest can be connected at pleasure. Two or more change wheels, properly proportioned as to the number of their teeth, connect the head of the screw with the hinder end of the mandrel. Although a leading screw is not the only nor in all cases the best mode of rendering a lathe self-acting, ordinary screw-cutting lathes are very largely used for other pur poses than that implied by their name. The advantage of perfect regularity in the feed is very great even for plain turning, and this can only be secured when it is inde pendent of human vigilance. The feed in a direction
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