外文原文： Machining Turning The engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirable attributes. Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encountered. The engine lathe has been replaced in todays production shops by a wide variety of automatic lathes such as automatic tracer lathes, turret lathes, and automatic screw machines. All the advantages of single-point tooling for maximum metal removal, and the use of form tools for finished on a par with the fastest processing equipment on the scene today. Tolerances for the engine lathe depend primarily on the skill of the operator. The design engineer must be careful in using tolerances of an experimental part that has been produced on the engine lathe by a skilled operator. In redesigning an experimental part for production, economical tolerances should be used. Turret Lathes Production machining equipment must be evaluated now, more than ever before, in terms of ability to repeat accurately and rapidly. Applying this criterion for establishing the production qualification of a specific method, the turret lathe merits a high rating. In designing for low quantities such as 100 or 200 parts, it is most economical to use the turret lathe. In achieving the optimum tolerances possible on the turret lathe, the designer should strive for a minimum of operations. Automatic Screw Machines Generally, automatic screw machines fall into several categories； single-spindle automatics, multiple-spindle rapid, automatic chucking machines. Originally designed for rapid, automatic production of screws and similar threaded parts, the narrow field, and today plays a vital role in the mass production of a variety of precision parts. Quantities play an important part in the economy of the parts machined on the automatic screw machine. The cost of the parts machined can be reduced if the minimum economical lot size is calculated and the proper machine is selected for these quantities. Automatic Tracer Lathes Since surface roughness depends greatly upon material turned, tooling, and feeds and speeds employed, minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerances. In some cases, tolerances of 0.05mm are held in continuous production using but one cut. Groove width can be held to 0.0125mm on some parts. Bores and single-point finishes can be held to 0.0125mm. On high-production runs where maximum output is desirable, a minimum tolerance of 0.125mm is economical on both diameter and length of turn. Milling With the exceptions of turning and drilling, milling is undoubtedly the most widely used method of removing metal. Well suited and readily adapted to the economical production of any quantity of parts, the almost unlimited versatility of milling process merits the attention and consideration of designers seriously with the manufacture of their product. As in any other process, parts that have to be milled should be designed with economical tolerances that can be achieved in production mill. If the part is designed with tolerances finer than necessary, additional operations will have to be added to achieve these tolerances-and this will increase the cost of the part. Grinding Grinding is one of the most widely used methods of finishing parts to extremely close tolerances and fine surface finishes. Currently, there are grinders for almost every type of grinding machine required. Where processing costs are excessive, parts redesigned to worthwhile. For example, wherever possible the production economy of centerless grinding should be taken advantage of by proper design consideration. Although grinding is usually considered a finishing operation, it is often employed as a complete machining process on work which can be ground down from rough condition without being turned or otherwise machined. Thus many types of forgings and other parts are finished completely with the grinding wheel at appreciable savings of time and expense. Classes of grinding machines include the following: cylindrical grinders, centerless grinders, internal grinders, surface grinders, and tool expense. The cylindrical and centerless grinders or taper work； thus splines, shafts, and similar parts are ground on cylindrical machines either of the common-center type or the centerless machine. Thread grinders are used for grinding precision threads for thread gages, and threads on precision parts where the concentricity between the diameter of the shaft and pitch diameter of thread must be held to close tolerances. The internal grinders are used for grinding of precision holes, cylinder bores, and similar operations where bores of all kinds are to be finished. The surface grinders are for finishing all kinds of flat work, or work with plain surfaces which may be operated upon either by the edge of a wheel or by the face of a grinding wheel. These machines may have reciprocating or rotating tables. 譯文： 機械加工 金屬切削機床中最早的一種是普通車床，當今仍有許多 有用的特性。可是目前，這些機床主要用在較小規(guī)模的工廠中，進行較小規(guī)模的生產，而不用做大批量的生產。 當前的生產車間中，種類繁多的自動車床已經取代了普通車床。比如自動仿形車床，六角車床和自動螺絲車床。現(xiàn)今，設計人員已經熟習的知道了先用單刃刀具去除大量的金屬余量，后用成型刀具獲得精度和表面粗糙度這種加工方法的優(yōu)點。它的生產速度和現(xiàn)在工廠中使用的最快的加工設備相等。 操作者的技術熟練程度是影響普通車床加工偏差的重要因素。設計工程師要認真的確定由熟練工人在普通車床上加工的試驗零件的公差。在把試驗零件做為生產零件時， 應選用比較經濟的公差。 六角車床 從生產加工設備這方面看，現(xiàn)在比以往更著重評價是否具有精度和快速加工的能力。評價具體的加工方法用這個標準，六角車床可以獲得較高的質量評定。 在設計小批量的零件加工方法時，最經濟的是采用六角車床。同時，為了獲得最小的公差，設計人員應盡最大限度的減小加工工序的數(shù)目。 自動螺絲車床 通常的它的類型可分為以下幾種；單軸自動、多軸自動和自動夾緊車床。它最初是被用來對螺釘和類似帶有螺紋的零件進行自動加工的?？墒?，此種車床的用處已經早就超出了這個范圍。如今，在很多種類精密零件的大批量生產中 它起著重要的作用。所加工零件的數(shù)量，用自動螺絲車床對它的經濟性有較大的影響。若工件的數(shù)量少于是 1000 件，六角車床上加工要比自動螺絲車床上加工經濟的多。若算出最小經濟批量，并且針對工件批量正確地選擇機床，零件的加工成本就會自然的降低。 自動仿形車床 因為零件的表面粗糙度主要是取決于件材料、刀具、進給量、和切削速度，所以用自動仿形車床加工所得到的最小公差不一定是最經濟的公差。 如在一些情況下，連續(xù)生產的過程中，只進行一次切削加工時的公差可以達到 0.05mm。對一些零件，槽寬的公差 0.125mm。采用單刃 刀具和鏜孔進行精加工時，公差可達到 0.0125mm。在希望得到的產量的大批量生產中，直徑和長度上的切削時的最小公差值為 0.125mm 是經濟的。 銑削 把車削和鉆削除外，應用最廣泛的金屬切削方法就是銑削。它很適合用在任何數(shù)量的零件的經濟生