【正文】 Nose radius. Tool angle 1, on front view, is the backrake angle. It is the angle between the tool face and a line parallel to the base of the shank in a longitudinal plane perpendicular to the tool base. Then this angle is downward from front to rear of the cutting edge, the rake id positive。 when upward from front to back, 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 in 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 the base and the end flank immediately below the end cutting edge。 but the possibility of chatter increases. A promise must, as usual, be reached. The nose angle, number 8, is the angle between the two ponent cutting edges. If the corner is rounded off, the arc size is defined by the nose radius 9. the radius size influences finish and chatter. Cutting Tool Materials A large number of cutting tool materials have been developed to meet the demands of high metalremoval rates. The most important of these materials and their influence on cutter design, are described below. High Carbon Steel. Historically, high carbon steel was the earliest cutting material used industrially, but it has now been almost entirely superseded since it starts to temper at about 220℃ and this irreversible softening process continues as temperature increases. Cutting speeds with carbon steel tools are therefore limited to about (30ft/min) when cutting mild steel, and even at these speeds a copious supply of coolant is required. Highspeed Steel. To overe the low cutting speed restriction imposed by plain carbon steels, a range of alloy steels, known as highspeed steels, began to be introduced during the early years of this century. The chemical position of these steels varies greatly, but they basically contain about % carbon and 4% chromium, with addition of tungsten, vanadium, molybdenum and cobalt in varying percentages. They maintain their hardness at temperatures up to about 600℃ , but soften rapidly at cutting speeds in excess of (350ft/min), and many cannot successfully cut mild steel faster than (150ft/min). Sintered Carbides. Carbide cutting tools, which were developed in Germany in the late 1920s, usually consist of tungsten carbide or mixtures of tungsten carbide and titanium or tantalum carbide in powder form, sintered in a matrix of cobalt or nickel. Because of the paratively high cost of this tool material and its low rupture strength, it is normally produced in the form of tips which are either brazed to a steel shank or mechanically clamped in a specially designed holder. Mechanically clamped tool tips are frequently made as throwaway inserts. When all the cutting edges have been used the inserts are discarded, ad regrinding would cost more than a new tip. The high hardness of carbide tools at elevated temperatures enables them to be used at much faster cutting speeds than highspeed steel (of 34m/s（ 600800ft/min） when cutting mild steel). They are manufactured in several grades, enabling them to be used for most machining applications. Their earlier brittleness has been largely overe by the introduction of tougher grades, which are frequently used for interrupted cuts including many arduous facemilling operations. Recently, improvements have been claimed by using tungsten carbide tools coated with titanium carbide or titanium nitride (about coating thickness). These tools are more resistant to wear than conventional tungsten carbide tools, and the reduction in interface friction using titanium nitride results in a reduction in cutting forces and in tool temperatures. Hence, higher metal removal rates are possible without detriment to tool life or alternatively longer tool lives could be achieved at unchanged metal removal rates. The uses of other forms of coating with aluminum oxide and polycrystalline cubic boron nitride are still in an experimental stage, but it is likely that they will have important applications when machining cast iron, hardened steels and high melting point alloys. Ceramics. The socalled ceramic group of cutting tools represents the most recent development in cutting tool materials. They consist mainly of sintered oxides, usually aluminu