The mandril by this means runs very steady and accurately in its bearings; and it is plain that any piece of work being firmly attache d to the end of it, by means of the screw before-mentioned, may be turned by a tool held over the rest, in the same manner as if it was mounted between centres, but with the advantage that it be turned at the end,to make hollow work when required. The foot-wheel causes the mandril to revolve very rapidly, so that it will perform its work very quick, and the Workman must acquire a habit of standing steady before his work, that he does not give his whole body a motion when his foot rises and falls with the treadle I.
The tools used in turning arenumerous, and for the most very simple; they consist chiefly of chisels and gouges, and hooked tools, with edges differently beveled, so as to adapt them to their peculiar objects; tools with serrated edges for cutting solid and hollow screws; callipers of several kinds, gauges, oil-stone, etc. To describe all these things and their peculiar uses, would occupy too large a space; we therefore proceed to notice some of the more important apparatus and improvements which have been of late years made in lathes, and with which some of our readers are perhaps not yet acquainted.
A very elegant and useful lathe, especially for amateur turning, was many years ago made by Mr. Henry Maudslay, of London. The most important feature in this improved turning machine, was the substitution of a triangular or prismatic bar, upon which the rest and centre puppet are constructed so as to slide, instead of sliding between parallel rectangular cheeks, as in the last we described. Since the first introduction of this lathe, (about 30 years since,) the triangular bar has been universally applied in lathes of the best kind. Some of the appendages introduced with Maudslay's lathe are particularly deserving of attention.
The first we shall describe is the universal chuck, of which the subjoined figure will convey an accurate conception. At a is a hollow screw, at the bottom of which is another screw, b b, which is prevented from moving endwise by a collar in the middle of it. One end of the screw is cut right-handed and the other left-handed; so that by turning it one way, the nuts c d will recede from each other, or by turning it the contrary way, they will advance towards each other. These two nuts pass through grooved openings in the plate e, and project beyond the same, carrying jaws like those of a vice, by means of which the substance to be turned is held.
Another very important and useful appendage to Mr. Maudslay's lathe, was his slide rest, which instrument is now universally employed in the best kind of lathes, for turning the faces of wheels, hollow work, and numerous other purposes. Since its introduction it has received many valuable modifications. It is represented in the subjoined engraving. At a a is a triangular opening to receive the triangular bar before mentioned, which is closed against the lower surface of the bar by means of clamps and screws, not represented. The tool for cutting is fixed in the two holders b b, by their screws; these holders are fastened by a sliding plate c, which can be moved backward and forward by the screw d, causing the tool to advance or recede. When it is necessary, as the turning of the insides of cones, etc, that the tool should not be parallel to the spindle of the lathe, the screw at e, and another similar one behind, must be loosed, so as to allow the circular plate under the box f, to turn upon its centre.
Near the four upper corners of the lower portion of the rest are small projections, two of which g g are seen; they have inclined sides, and fit into corresponding angular openings h h of the upper part of the instrument, which slides or rises between the piece i and the base k, in such a way as to prevent any other than a vertical motion. When this slide tool is placed on the bar to be used, the distance from the centre is adjusted by the screw l, which moves the slide m in its groove, and all the apparatus upon it; while by the screw n the slide may be moved in a direction perpendicular to the bar, and the projections acting in the slits h h, the plate o will be raised or lowered as required.
Such lathes as we have already described, are not well adapted to the turning of long rods and cylinders, such as are required in large steam-engines and various massive machinery, on account of the necessity of repeatedly shifting the rest, and the difficulty of keeping the work perfectly uniform in thickness through a considerable length. Engineers therefore facilitate the turning of such surfaces by means of another machine called a slide lathe, by which the work is performed with great ease and exactness. The principle of this invention consists in so constructing and attaching the body or carriage of the rest, that instead of being screwed down to one place during the operation of the tool, and requiring to be advanced at intervals as the work proceeds, it shall slide along the surface of the bench in a direction parallel to a line drawn through the centre of the spindle. At the same time the tool, instead of being merely held upon the rest with the fingers, is firmly fixed in itsproper position by screws, so that it can neither be driven off without taking effect, nor yet be drawn by its keenness so as to spoil the work.
The whole is managed in such a way that, as the iron to be turned revolves between the centre points, the rest, with its cutter or chisel advances slowly along in a certain direction, so as to produce a perfectly level rod. But besides the exactness attainable by this method, there is likewise the advantage of economy; as one man, who would with hard labour apply the tool to one point at once at a common lathe, may easily attend to, and keep in work, two or three slides.