We may here notice a contrivance, introduced by Mr. Miles in 1850, for turning pieces of wood so long that they would vibrate or swag if operated upon in the ordinary way. The wood does not rotate. The cutters along it and turn mem/ it, being supported by a travel im; carriage. Two dogs or IT qa are placed beneath the wood at certain strong plate which screws on the nose of the mandril ; two dovetailed pieces are screwed upon it near the edges, between which the elide, a, works. Upon the slide is fitted a circular plate, which turns upon a centre, and has its edge cut into a number of teeth according to the size of the chuck ; e is a click with one or two teeth fitting between the teeth of the wheel, and held in its place by a spring under the other eta The nose, for carrying the work, is fixed to the upper plate. The denUe excentric chuck is made in the same manner, but it has a second slide, at right angles to the first, on the back of the ground plate. In common turning the use of the eccentric chuck Is to bring any required point in the work in a line with the centre of the mandril ; thus circular holes may be cut in any part of a plate, the edge may be hollowed out by any number of curves of the same or different radii, and polygons with curvilinear sides may be produced with the greatest accuracy. Pigs. 14,15, and 16 represent three among an infinite variety of figures produced in this way. In ornamental turning the eccentric chuck is mostly used for cutting patterns upon the surface of the work without altering its general outline. Thus, in ornamenting ivory or wood-work, circles and curves are laid in an infinite variety of positions upon the face end edges of the work. The ivory-turner frequently uses a small instrument called en Gwent)* cutter; it is formed like the drill-stock, fig. 11, and moved by a bow ; the cutting point can be fixed at different distances from the centre by means of a groove end screw. In conjunction with a click plate upon the mandril, the cutter answers many of the purposes of the single eccentric chuck. With the single-slide excentric chuck and the man dril at rest, the cutter will produce patterns which would otherwise require the double excentric.
°remark Turning.—When the work revolves on the lathe, and the eccentric cutter is driven by a Land in connection with the mandril, a great variety of very complicated and beautiful epicycloidal and other curves may lk cut. This geometric chuck is en eccentric with the addition of an arrangement for giving motion to the work upon the chuck, and independent of the mandril. Fixed to the headstock and concentric with the mandril is a toothed wheel which, as the chuck revolves, drives another and smaller wheel on its under surface: this latter is connected with another toothed wheel which causes the click plate and work to revolve. The patterns may be infinitely varied by altering the relative sizes of the wheels ; and by introducing an extra wheel, and sio emoting the work and chuck to revolve in opposite directions at the same time ; and lastly by changing the position of the tool. The number of different curves that can be produced by these changes and the great dissimilarity to each other can hardly be conceived. The eccentric and geometric chucks ere much used in producing patterns on plates end blocks for printing and embossing.
Oral Turning.—Until the invention of the oval chuck the production of true ovals was a matter of considerable difficulty, end the cutting of them upon the lathe an impossibility ; with it we can turn ovals of all sizes and proportions with almost the same ease as circles. The construction of the chuck is simple. Upon the front of the head stock, H, fig. 17, is placed a ring, held by screws through its two arms and the projecting pieces on each side of the headstock ; a screw is placed in one arm of the ring to draw it out excentric to the mandril. Fig. 18 shows the front of the chuck with a slide moving between dove tails on a ground-plate; the ground-plate, as shown in jig. 19, has two into the bottom of the headstock is a strong arm, it (fig. 21), with a square hole near the bottom, to receive a smaller arm pierced with slits cut from the centre boss, which screws on to the 'mandril, nearly to the circumference; two small studs are cast upon the back of the slide, which are made to work easily in the two slits, and stand up just above the face of the ground-plate. When the slide is in its place two steel rubbers with straight polished faces are screwed to the studs, and stand out at the back of the ground-plate at right angles to the slits, as seen in fie. 19. The ring being fixed in its place upon the headstock, the chuck is screwed upon the mandril, the rubbers clasping the ring, which must be kept perfectly smooth and well oiled ; the excentricity of the ring, acting upon the rubbers, draws the slide out of the centre in opposite directions alternately, and upon the tool being applied an oval will be described upon the face of the work, having the shorter diameter in proportion to the distance of the tool from the centre, and the longer to the excentricity of the ring. For ornamental work the oval chuck is provided with a
click and sometimes a micrometer plate, like the excentric chuck, for placing the ovals in different directions.
Rose-engine Turning.—Of all the different sorts of ornamental turning this is by far the best adapted for embellishing small articles. It is in very general use for gold, silver, and gilt-work ; it is besides applied to the production of ground tints, borders, and ornaments on copper, steel, and wood rollers for printing and embossing calico, leather, and paper ; and many other sorts of ornamental work. An unsteady lathe, which in revolving produces an irregular circle, is a rude approach to the rose-engine, and may very possibly have furnished the first hint for its invention. We shall now describe it. u (fig. 20) holes ; one end of this latter is attached to a strong spring, s, and by placing a pin in one or other of the holes in the small arm, the spring may be made either to press or pull the arm h with less or greater force. The rubber-carriage T being moved along the bar n till the end of the rubber is exactly opposite the face of the rosette to be employed, and fixed there by the back-screw, the spring set to pull the arm it, and the side screws in the standards A turned back until the face of the rosette rests upon the rubber a, the engine at each revolution will pro duce a copy of the indentations upon the face of the rosette. The engine is moved by a band-winch with a band passing round a foot wheel, and another connecting a small pulley on the crank with the mandril-pulley E, in the same manner as the slow motion of the foot lathe (fig. 2). The slide-rest is adapted to the rose-engine in the fol lowing way. The tail-piece of the rest F (figs. 20, 22) has a hollow is a headstock, supported upon the conical points of two screws, c c, in the two metal standards, A A, fitted and bolted to the bench or bed. In the front and back of the headstock, near the bottom. are two sunk centres to receive the conical points of the screws. The screws are secured by washers that run upon them, and tighten against the standards. The upper part of each standard carries two other screws at right angles to those described, for the purpose of holding the head stock steady when the rose-engine is to be used as a common lathe. Two of these screws are shown in the front of the engine (fig. 21). Upon the mandril are mounted the pattern guides, or rosettes, circular plates of gun-metal or brass, each about half an inch thick, and having two patterns or waves upon its rim. The rosettes are of two sorts, fixed and shifting. The fixed, F, are screwed to a collar turned upon the mandril itself ; the moveable, n, are fixed upon a cannon, B (fig.20); the plate u is fixed to the cannon, and the rosettes are prevented from turning by a feather which fits into a notch in each of the rosettes : a nut at the end of the cannon screws all tight against the plate u. The plate D is put on the mandril at the back of the cannon plate m, but independent of both; behind this is another plate, r, fitted on to the mandril. and turning with it ; at the back of this plate is a nut, which is tightened until the cannon requires some little force to turn it upon the mandril with the hand. On the large plate r, is a spring-click, which falls into notches cut in the plate D, which itself carries an end less screw working into a half thread cut on the edge of the cannon plate it. T is a carriage for holding the rubber n, by means of the two screws in the top of the carriage : the rubber is a small bar of steel, three or four inches long, and the breadth of the rosettes. screwed cylinder, c, fixed in the middle of one end. The bar a, which has a piece at each end fitting into dovetails in the sides of A, has a cylindri cal piece which fits accurately into the hollow cylinder c, and can be raised or lowered at pleasure by a ring or nut, N, working upon the outside of C, the rest being placed in the required position, and fixed to the bench by the screw s (fig. 2.1). The stock A moves round upon the cylinder c, and can be fixed at any required angle by the binding nut o. The top of the rest, which traverses along the bar B, by means of a screw throughout its length, provided with an index-plate and winch-handle, a, is composed of two parts, the ground plate (fig. 2:3) and another plate (fig. 24), which carries the tool-slide. The engine is also capable of turning the sides and edges of work, for which purpose it is provided with a separate set of waves cut upon the aides of the rosettes, some of which are made of larger diameter than others for that purpose. The rubbers arc shaped at the side to correspond; the mandril has an endway-motion within its bearings, and is acted upon in either direction by the lever-spring et (fig. 20), which has its fulcrum upon the bench : its upper end is forked, and fits a groove in the mandril, and the lower held by an arm and pin. For side-work the slide-rest is placed parallel with the bench as in common turning.