The most widely employed of all machine tools is the turning lathe. By means of it, all sorts of cylindrical work are fashioned, besides a great variety of other forms. Lathes are of three general types - hand, foot, and power - depending on the source from which the motion is derived. The ordinary modern lathe is provided with a planed metal bed fixed on metal standards. Two heads are supported on the bed or shears, the one at the left called the running or fixed head, the other the moving, shifting, or poppet head. The running head is usually supplied with a stepped cone, corresponding to one on the counter shaft, by means of which the speed of the machine may be changed at will. The second, or back motion, supplied to most power lathes, is for the same purpose, and is resorted to when a very slow speed is required. The cone and spindle are fixed together by means of a screw, which must be moved before the back motion can be started. This will allow them to revolve independently. The back motion is brought into gear with the wheel and pinion on the spindle by the use of two eccentrics, and kept in position by a pin passing through the head. Each head is fitted with a hardened, conical, cast-steel centre, which supports, and keeps in position, shafting and such like work. The point of the running head spindle is provided with a screw, on which all chucks and face plates are fixed when in use. These lathe adjuncts are chiefly employed to hold the work in position for turning, and are of many forms. The shifting head is fixed in position by a bolt; but for small movements, the spindle may be altered by an internal screw, on which the hand wheel is fastened. When properly set, the spindle is held fast by another screw, to prevent accidental movement. Most power lathes have self-acting slide rests and tool holders combined, and are supplied with two motions - one parallel to the the axis of the lathe, and the other at right angles to it. The speed of these motions may be changed by the use of different trains of wheels, from which the movement is conveyed by a screw to the slide rest. Any lathe, having such automatic movement, is called a self-acting, screw-cutting turning lathe, for, by means of it all sort of screws may be cut with perfect regularity. All power tools ought to be provided with fast and loose pulleys, so that they may be started and stopped at will. The speed of a lathe depends on the material being turned, and its diameter; 25 feet of surface per minute being about the average. The different operations in metal turning will be most easily understood by following the production of a small cylindrical piece of iron, say 12 ins. long and 1 in. in diameter. In procuring the rough stock, sufficient allowance for turning must be made in both length and diameter. After cutting, the ends must be chipped, filed or hammered, so that the centres may be readily marked. By means of a jenny callipers, the centre point of each end may be found, the ends having been chalked to show the marks clearly. A small conical centre should now be formed with the centre punch, after which the piece of iron must be put between the lathe centres, and fixed so as to be readily revolved by one hand, while with the other, a piece of chalk should be applied to mark the high parts. This must be done at both ends, after which the piece of iron should be taken out, put into the vice end up, and the centre shifted as much as may be considered necessary. It must now be replaced between the centres, and tested again, the process being continued until the ends run true. Meantime the other parts along the length ought to be tried in the same manner, and hammered till straight. When found to run truly through its entire length, a small hole about a 1/16 in. in diameter and an 1/8 in. deep, should be drilled into the piece of iron at the bottom of each centre, to provide for lubrication, and insure continued truth. A driving chuck must be put upon the running head spindle, and into it one or two pins fixed. These pins come into contact with the carrier, screwed on one end of the work, to which the motion, imparted to the lathe, is transmitted. After the carrier is fixed in its place, and the work put between the centres ready for turning, the proper tools must be selected and sharpened. All metal cutting tools must, like those for wood working, have a small angle of clearance, while the cutting angles vary from 6o° to 900, the former being suitable for wrought-iron and steel, while cast-iron and brass require a much greater angle. Roughing tools are of an angular form at the point, and slightly rounded; whereas finishing or planishing tools are flat on the face, and sharpened to an acute edge with the set-stone. If the lathe is provided with a self-acting movement and tool holder, then the tool must be placed, so that the cutting edge may be about level with the centre of the work, or slightly below it, and firmly fixed in that position. No lathe should be set in motion until it has been ascertained that all moving parts are clear. This may be easily decided by turning the cone one revolution with the hand, after which it may be started with assurance. The running parts should be kept well supplied with oil to prevent heating. Water is used in turning wrought-iron and steel to keep the tool cold, but not in the case of cast-iron and brass. The turnings and waste water are caught in a box below the tool, the water being supplied from a small can above, provided with a drip pipe and tap. When the tool has been brought in contact with the work so as to give the depth of cut required, the self-acting motion in the direction parallel to the axis of the work is started, which will cause a cut to be removed from the surface. This can only be done for part of the length, as the carrier prevents the entire surface being operated upon. A series of cuts would thus be removed until within about a 1/64 in. of the required diameter, which would be left for finishing. When one end is roughed down the carrier may be shifted and the other end similarly treated.