Page:The American Cyclopædia (1879) Volume XVI.djvu/86

 7 TURNING defined manner and degree, while the work is rotated and the tool continually acting upon it. This species of turning, with a variable centre of the work at different moments, takes sever- al names according to the devices employed or the particular results secured, as eccentric, geometric, oval, and rose-engine turning. Such work is said to be figure-turned ; and the gen- eral principle is that of employing some form of chuck which shall give an oscillation or lat- eral movement to the axis or the work during its revolutions, so as to insure those deviations from a simple circular application of the cutter required for the intended form or figure. The chucks employed are designated as the eccen- tric, the geometric, the oval, or more properly elliptical, and as rosettes ; while a straight line chuck can also be employed to cut plane sur- faces or square work. In all work of this character, the amateur turner prides himself not only on the delicacy and elegance of his results, but quite as much on the difficulty of execution; and the value of turned work is often estimated by the degree in which it de- parts from the circular figure. For eccentric turning, a single eccentric chuck is one fixed upon a strong plate that can slide laterally within straight guides screwed upon the face of the mandrel, and which, having upon it a toothed wheel and click, is called the click plate ; the slide, and the nose upon it for car- rying the work, can be shifted into various positions out of centre, before applying the cut- ter. In the double eccentric chuck, a second plate or slide at the back of the first, and at right angles to it, can further vary the position of the axis. By aid of such a chuck, any re- quired part of a disk can be brought in lino with the centre of the mandrel, and holes bored in any part of it, or the edges hollowed out in curves of like or different radii, or polygons with curvilinear sides accurately produced. Ornamental work with these chucks consists mostly in the execution of variously curved figures on surfaces, without cutting away or changing the general outline, as in ornament- ing ivory or fine work in wood. The ivory turner often employs a small instrument called an eccentric cutter, in which the tool revolves rapidly, being moved by a bow, and with which, by means of a single eccentric chuck and a separate adjustment of the cutter, in- volved figures like those ordinarily requiring the double eccentric chuck are produced. For geometric turning, a chuck of similar name is employed. In this, a wheel concentric with the mandrel, while the latter and the chuck revolve, gives, by means of a train of smaller wheels, an independent movement to the click plate and axis of the work. By varying the relative sizes of the wheels, by introducing an added wheel to cause the work to turn at the same time in a direction the reverse of that of the mandrel, and by changing the position of tne_tool, or giving movement at the same time to it, an almost infinite variety of curiously TURNIP involved curved figures may be engraved or marked upon a plane surface to which motion ia thus imparted under the point of the tool By this machine some of the most perfect ro- settes and other lathe work of bank notes, in the United States largely relied on as a means for the prevention of successful counterfeiting, are executed. The figures will vary with the construction of the machine; of which, save by actual inspection or model, no duplicate can be constructed. The geometric lathe of the American bank-note company of New York, the single one of its kind, is a foot lathe of highly complicated and perfect workmanship, the construction of which is said to have occu- pied three years' time, at a cost of $10,000. Elliptical turning is accomplished by means of the elliptical or oval chuck, in which the pres- sure of an eccentric ring, moving within and clasped by rubbers, is made to draw the slide out of centre alternately in the opposite direc- tions, so that a stationary tool, held to a plate to which this movement is imparted during a revolution of the mandrel, will describe an ellipse instead of a circle ; while the size, direc- tion, and form of the ellipses can also be va- ried ; and, as in the other forms of lathe hero described, the micrometer screw may be intro- duced for determining the accuracy of pro- portions in the work. Of the few machines which have been invented for turning irregu- lar forms, in heavy or ordinary work, that of Blanchard is perhaps the best known and most successful. The principle of this machine is, that forms are turned by a pattern the exact shape of the object to be produced, which in every part of it is successively brought in con- tact with a small friction wheel ; this wheel precisely regulates the motion of chisels ar- ranged upon a cutting wheel acting on the rough block, so that as the friction wheel suc- cessively traverses every portion of the rota- ting pattern, the cutting wheel pares off the superabundant wood from end to end of the block, leaving a precise resemblance of the model. This remarkable machine, with modi- fications and improvements, is in use in the national armories as well as in England, and in various forms is applied to many operations in making musket stocks, such as cutting in the cavity for the lock, barrel, ramrod, butt plates, and mountings, comprising, together with the turning of the stock and barrel, 13 different machines. Besides gun stocks, it is also applied to a great variety of objects, such as busts, shoe lasts, handles, spokes, &c. For further information respecting the tools and materials used in turning, see Holtzapffel'8 " Turning and Mechanical Manipulations" (8 vols., London, 1847-'52) ; and for the general subject, see the article "Lathe" in "Apple- tons' Dictionary of Machines," &c. (New York, 1857), and Valicourt's Nouveau manual com- plet du tourneur (3 vols., Paris, 1848-'58). TURNIP, a variety of brassica campestris, hav- ing two very marked forms: one with small