【正文】 the means for mounting and moving cutting tools. The carriage is a relatively flat Hshaped casting that rests and moves on the outer set of ways on the bed. The transverse bar of the carriage contains ways on which the cross slide is mounted and can be moved by means of a feed screw that is controlled by a small handwheel and a graduated dial. Through the cross slide a means is provided for moving the lathe tool in the direction normal to the axis of rotation of the work. On most lathes the tool post actually is mounted on a pound rest. This consists of a base, which is mounted on the cross slide so that it can be pivoted about a vertical axis, and an upper casting. The upper casting is mounted on ways on this base so that it can be moved back and forth and controlled by means of a short lead screw operated by a handwheel and a calibrated dial. Manual and powered motion for the carriage, and powered motion for the cross slide, is provided by mechanisms within the apron, attached to the front of the carriage. Manual movement of the carriage along the bed is effected by turning a handwheel on the front of the apron, which is geared to a pinion on the back side. This pinion engages a rack that is attached beneath the upper front edge of the bed in an inverted position. To impart powered movement to the carriage and cross slide, a rotating feed rod is provided. The feed rod, which contains a keyway throughout most of its length, passes through the two reversing bevel pinions and is keyed to them. Either pinion can be brought into mesh with a mating bevel gear by means of the reversing lever on the front of the apron and thus provide “forward” or “reverse” power to the carriage. Suitable clutches connect either the rack pinion or the crossslide screw to provide longitudinal motion of the carriage or transverse motion of cross slide. For cutting threads, a second means of longitudinal drive is provided by a lead screw. Whereas motion of the carriage when driven by the feedrod mechanism takes place through a friction clutch in which slippage is possible, motion through the lead screw is by a direct, mechanical connection between the apron and the lead screw. This is achieved by a split nut. By means of a clamping lever on the front of the apron, the split nut can be closed around the lead screw. With the split nut closed, the carriage is moved along the lead screw by direct drive without possibility of slippage. Modern lathes have a quickchange gear box. The input end of this gear box is driven from the lathe spindle by means of suitable gearing. The output end of the gear box is connected to the feed rod and lead screw. Thus, through this gear train, leading from the spindle to the quickchange gear box, thence to the lead screw and feed rod, and then to the carriage, the cutting tool can be made to move a specific distance, either longitudinally or transversely, for each revolution of the spindle. A typical lathe provides, through the feed rod, fortyeight feeds ranging from inch to inch per revolution of the spindle, and, through the lead screw, leads for cutting fortyeight different threads from to 92 per inch. On some older and some cheaper lathes, one or two gears in the gear train between the spindle and the change gear box must be changed in order to obtain a full range of threads and feeds. CUTTING TOOL Shape of cutting tools, particularly the angles, and tool material are very important factors. The purpose of this unit is to introduce the cutting tool geometry and tool materials. Cutting Tool Geometry Angles determine greatly not only tool life but finish quality as well. General principles upon which cutting tool angles are based do not depend on the particular tool. Basically, grinding wheel are being designed. Since, however, the lathe (turning) tool, depicted in , might be easiest to visualize, its geometry is discussed. Tool features have been identified by many names. The technical literature is full of confusing terminology. Thus in the attempt to clear up existing disorganized conceptions and nomenclature, the American Society of Mechanical Engineers published ASA Standard B5221950. what follows is based on it. A singlepoint tool is a cutting tool having one face and one continuous cutting edge. Tool angles identified in Fig. 142 are as follows: (1) Backrake angle, (2) Siderake angle, (3) Endrelief angle (4) Endrelief angle (5) Siderelief angle (6) Endcuttingedge angle, (7) Sidecuttingedge angle, (8) Nose angle, (9)