Bending Rolls and Benders are used gen erally in boiler and tank work; the metal plates being drawn by rotation between three rolls so arranged that their axes form the edges of a triangular prism, their relative adjustment de termining the curve to which the plate is bent.
Rolling Machines are used to flatten out metal bars into plates and commercial shapes, such as I-beams, railroad rails; etc. As de signed at present they accomplish in a short space of time a great variety of work which in times past was turned out by the mote labori ous and expensive processes of lathe turning and forging. One class is used to manufac cure boiler and armor plate and the gene run of heavy sheet metal; while another ;I produces the thin sheet metal down to the finf grades such as tinfoil.
Presses.— By the use of presses sheeT plate metal is converted into utensils of desired form. They are usually operated hydraulic power; are provided with dies tween which the metal is pressed into the quired form, and are capable of being structed to exert an unlimited amount of TY sure. Forging presses are made in all st• adapted for uses ranging from the pressim watch-cases to the forging of steamship sh. and of armor plates weighing up to 141• pounds. Forgings thus made are superior hammered forgings. They are designed n working metals either hot or cold.
Platters.-- Planing machines are' nsed m ex min flat . surfaces on metal. There are is, types; those in which the motion of the tahlt relative to the cutting tool is rectilinear an those 'in which that motion is rotary. In era eral construction a planer consists of a trave ing table on which the work is fastened; a be' to receive the table and guide it in a right lint a cross slide to support the slide rest carryis the tool; standards bolted to the bed and sip porting, the'cross slide, and the mechanical de vices for feeding and regulating purposes. Tht power supplied from shafting by belts is trars. formed by gear-wheel attachments into the re ciprocating motion of the table, causing it : slide., back and forth between the vertict guides, thus bringing the work against the ca Ling tool which shaves off successively, side I side, narrow thin strips of metal until a per fectly flat „surface is produced. Planers an built in various sizes, the larger machines be= equipped with tables 7 to 8 feet in width and.a feet long.
Saws.—In metal working, saws •bniolirl• the class commonly termed finishing machiaer For cutting plates and bars into shorter iike• ate in extensive use, affording a grr.
economy of time They arc built in a many sizes and forms, both stationary and pan able, equipped with single cutters or cutters ar ranged in gangs. For cutting off large tur such as steel beams, rails and similar skapt saws with single cutters are generally used, t. object being fastened to a carriage and mevec into contact with the edge of the circular ter. Some machines used for lighter work : so arranged that the circular saws are tnovc into contact with the bars. The cutters are of two kinds. The friction discs made of soft mild steel, without teeth, measuring about 44 inches in diameter and three-sixteenths of an inch in thickness, are used for cutting off either hot or cold metal. They are rim at a high rate of speed, about 15,000 feet per minute, rim ve locity. The toothed cutters vary greatly in diameter and thickness; are made of highly tempered steel, and are used for clean cutting in cold metal. They are usually run at a low rate of speed, the rim velocity varying from 130 to 150 feet per minute. Friction discs run at rim velocities between 20,000 and 25,000 feet per minute are called fusion discs, from the fact that the intense heat generated by the friction actually melts the metallic dust ground off by the cutter.
Special Machines.— This term includes an almost endless variety of metal-working ma chinery, capable of enumeration only in a very general way. They are used for special pur poses such as making pins, nails, rivets and pens; the tapping of nuts and the threading of bolts. Although often of very complex con struction they turn out work with great rapidity and precision. In its special field metal-working machinery- has not only displaced band labor is all countries, and especially in the United States, but by its use structural work such as the building of magnificent buildings and bridges, powerful engines and mammoth ships have been produced fat beyond the capabilities of that which is known industrially as hand labor. Consult Adam, H. M., and Evans, I. H., 'Metal Work' (London 1914) • Colvin, F. H., and Stanley, F. A., 'American Machinist Grind ing Book' (New York 1912) ' • De Vries, D., 'Milling Machines and Milling Practice' (Lon don 1916) ' • Hasluck, P. N., 'Metal Working/ (London 1904) ; Horner, T. G., 'Modern Mill ing Machines' (London 1906) ; Pull, E., 'Mod ern Milling' (New York 1917).