【正文】 lem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major step forward in the further development of NC technology. The original NC systems were vastly different from those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development. A major problem was the fragility of the punched paper tape medium. It was mon for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each successive time a part was produced on a machine tool, the paper tape carrying the programmed instructions had to be rerun through the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use. This led to the development of a special magic plastic tape. Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magic dots. The plastic tape was much stronger than the paper taps, which solved the problem of frequent tearing and breakage. However, it still left two other problems. The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instructions, it was necessary to interrupt machining operations and make a new tape .It was also still necessary to run the tape through the reader as many times as there were parts to be produced. Fortunately, puter technology became a reality and soon solved the problems of NC associated with punched paper and plastic tape. The development of a concept known as direct numerical control (DNC) solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control .machine tools are tied, via a data transmission link, to a host puter. Programs for operating the machine tools are stored in the host puter and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend on a host puter. When the lost puter goes down, the machine tools also experience downtime. This problem led to the development of puter numerical control. The development of the microprocessor allowed for the development of programmable logic controllers (PLCs) and microputers. These two technologies allowed for the development of puter numerical control (CNC).With CNC, each machine tool has a PLC or a microputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. It also allows programs to be developed offline and downloaded at the individual machine tool. CNC solved the problems associated with downtime of the host puter, but it introduced another known as data management. The same program might be loaded on ten different microputers with no munication among them. This problem is in the process of being solved by local area works that connect microputers for better data management. Cutting Tool Geometry Shape of cutting tools, particularly the angles, and tool material are very important factors. 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, the same considerations hold true whether a lathe tool, a milling cutter, a drill, or even a grinding wheel are being designed. Since, however the lathe tool, depicted in Fig. , 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 cleat up existing disanized conceptions and nomenclature, this 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. are as follows: Tool angle 1, on front view, is the backrank angle. It is the angle between the tool face and a line parallel to the tool base of the shank in a longitudinal plane perpendicular to the tool base. When this angle is downward from front to rear of the cutting edge, the rake is positive。 when upward from front to black, the rake is negative. This angle is most significant in the machining process, because it directly affects the cutting force, finish, and tool life. The siderake angle, numbered 2, measures the slope of the face on a cross plane perpendicular to the tool base. It, also, is an important angle, because it directs chip flow to the side of the tool post and permits the tool to feed more easily into the work. The endrelief angle is measured between a line perpendicular to t