BENDING :MACHINES. Bending rolls are used for bending metal plates to suitable curves for boiler and lank work. They usually consist of three rolls arranged in the form of a triangle be tween which the plate is drawn by the rotation of the rolls. The relative adjustment of the rolls determines the curve to which the plate is bent. The accompanying plate shows a horizontal bend ing roll operated by a special steam-engine and teeth of an ordinary saw. It has generally been found more profitable, however, to saw iron with disks or hand saws, fitted with cutting teeth, which run at moderate speeds and cut the metals as do the teeth of a milling cutter such as is de scribed in the succeeding section. A novel appli cation of the cold saw is known as Reese's fusing disk. This saw is used to cut iron or steel in the form of bars, tubes, cylinders, etc., and the piece to be cut is made to revolve as well as the saw, but at a slower speed. By this means only a small surface of the bar to be cut is presented at a time to the circumference of the saw. The Saw is about the same size as the cold saw de scribed above, and is rotated at a velocity of about 25.000 feet per minule. The heat generated
by the friction of this saw against the small sur face of the bar exposed to its action at one time is so great that the particles of iron or steel in the bar are actually fused and the 'sawdust' welds into a solid mass as it falls. This disk Nvil I cut either east iron or wrought iron or steel.
Thm.txc machines are used for forming exact surfaces of various forms by means of revolving cutting tools or cutters. By means of different shaped cutters an almost unlimited variety of surfaces can be cut by mill ing machines. They are used extensively for shaping small articles such as and gun parts. They vary greatly in vertical, horizontal. and universal, with one or several cutters. Fig. tl shows a form of plain milling machine with a horizontal spindle, and Fig. 10 shows representative forms of ;miters and tools. of which there are many special shapes,