Page:The New International Encyclopædia 1st ed. v. 13.djvu/401

* METAL WORK. 367 METAL-WORKING MACHINERY. METAL WORK. A tunii usually applied to artistic wurk in metal. The metals generally used for tliis purpose are gold, silver, copper, iron, and lead, and the i)rineipal methods of treatment employed are casting and repousse. (For a description of these processes, see Found- ixo and Hei'OIS.se. ) By reason of its scarcity and value, gold has been generally used in the fine arts for small objects of luxury ami adornment, although the (ireeks frequently used it, in con- nection with ivory, for statues of great sanctity. (See CioLDSMiTii's Work; Jewelry.) The use of silver is also thus limited, though to a less extent. Although copper in a pure state was used for ecclesiastical ornaments from the twelfth to the fifteenth century, its chief use has always been as an alloy with tin in the form of bronze. In this form it is the metal most used in the fine aits, being more used than any other ma- terial except marble, both in statuary and relief. This is due to the fact that its high lluidity when melted, its slight contraction upon cooling, and its hardness render it peculiarly adapted for cast- ing, (See Bronze.) Brass, an alloy of copper and zinc, was also used during the Jliddle Ages for sepulchral slabs, the image being engraved upon the brass plate, (See Bras.ses, Sepul- chral. ) By reason of its great contraction upon cooling, iron is less adapted to casting; but its extreme malleability and adhesive qualities when heated render it easy to forge under the stroke of the hammer. From the thirteenth century to the eighteenth it was extensively used with high artistic success for screens, gates, and the like, though the attempted revival in our day can- not be pronounced eipially successful, (See Irox axi) Steel.) Steel is also extensively used in the beautiful inlay work of Oriental luitions. See Damaskeening; Inlaying; Indian Art. BiBLiOGRAPin'. The autliorities on the technique and history of the special kinds of metal work will he found under the titles cited above. Among the special manuals on the subject, which have been written at different periods, are: The treat- ise of the jIoid< Theophilus. '"Diversarum Artium Schedula" (twelfth century), published in Qiicl- hnschiiftcii fiir Kiinstgeschichie, ^'[[. (Vienna, 1877) ; Cellini, Trutia'li dclV oreficeriu c deUa scultnra, ed, Milanesi (Florence, I85G) ; Vasari, Tre arii del disegnq^. pt, ii.. ed. Milanesi (ib., 1882) ; Garnier, Manuel du ciselcur (Paris, 1859) ; Codron, Travail des metaiix duns les atHiers de construction mecanique (ib.. 1001); Haas, Der Metnllarheiter (Landeshut, Schlesien, n'n-2) ; Lc.ricrin drr MrhiJteehnik (Vienna, 1!)00). METAL-WORKING MACHINERY. The number and variety of metal-working machines are very large, the term comprehending prac- tically all machines by which metals are wrought into useful shapes. For ordinary purposes melal- working machines may be divided into the fol- lowing classes: Planing machinery or jdaners; turning machinery or lathes; boring machinery or drills; punching machinery or punches; milling machines; shearing machines or shears: riveting machinery or riveters; presses; bending machin- ery: saws; and special machinery. Planixo ■NIaciiine.s. Planing machines or planers are employed for working metal surfaces to accurate planes by cutting off the projections by the planing or cutting action of a suitable tool, past which the work reciprocates or revolves in a fixed plane. One of the most common forms of planing machines is shown by the illustration. (Fig. 3, Plate of Metal-Wokking Machinery.) The tool is carried by a tool head having a slid- ing motion on a cross-bar which can be moved up or down on two vertical guides. The table which carries the work clamped to it slides back and forth between the two vertical guides, and thus brings the work against the tool, which takes off a narrow, thin shaving of metal. By a suc- cession of such shavings following each other like the furrows of a plowed field, a plane surface is secured. Machines of this character are built in various sizes, some of them having tables 21 feet long and 7 feet wide. In rotary planers the work has a rotary motion with respect to the Fia. 1. DRILL. tool instead of a rectilinear motion. Planes for smoothing the edges of metal plates usually have the work clamped fast while the tool is carried along the edge taking off a thin shaving. Power is usually supplied to planing machines from shafting by means of belt transmission, and the rotary motion of the belt is transformed into the reciprocating motion of the table by means of gearing. When in operation the motion of the table and the motion of the tool head necessary to produce successive cuts are automatic, TiRNiNG Machinery or Lathes, Lathes are tools for producing cylindrical surfaces by ro- tating or turning a bar before a cutting tool. The bar to be turned is clamped between a fixed point at one end and a rotating di.sk at the other end, while the tool head and carriage move parallel with the axis of the bar, the tool removing a spiral shaving from the surface of the bar. Lathes are driven by belts from shafting or may be operated by electric motors. They are