外文翻译--车床及其切削加工(编辑修改稿)

外文翻译--车床及其切削加工(编辑修改稿)内容摘要：

movedtransversely upon it, on some type of keyed ways, to permit aligning the tailstock and headstock spindles. The third major ponent of the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 51 to 76 mm (2 to 3 inches) in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a handwheel and screw. The size of a lathe is designated by two dimensions. The first is known as the swing. This is the maximum diameter of work that can be rotated on a lathe. It is approximately twice the distance between the line connecting the lathe centers and the nearest point on the ways. The second size dimension is the maximum distance between centers. The swing thus indicates the maximum workpiece diameter that can be turned in the lathe, while the distance between centers indicates the maximum length of workpieee that can be mounted between centers. Engine lathes are the type most frequently used in manufacturing. llley are heavyduty machine tools with all the ponents described previously and have power drive for all tool movements except on the pound rest. They monly range in size from 305 to 610 mtn ( 12 to 24 inches) swing and from 610 to 1 219 mm (24 to 48 inches) center distances, but swings up to 1 270 mm (50 inches) and center distances up to 3 658 mm ( 12 feet) are not tmmo n. Most have chip pans and 8 a builtin coolant circulating system. Smaller engine lathes with swings usually not over 330 mm ( 13 inches) also are available in bench type,designed for the bed to be mounted on a bench or cabi. Although engine lathes are versatile and very useful, because of the time required for changing and setting tools and for making measurements on the workpiece, they ale not suitable for quantity production. Often the actual chipproduction time is less than 30% of the total cycle time. In addition, a skilled machinist is required for all the operations, and such persons are costly and often in short supply. However, much of the operator39。 s time is consumed by simple, repetitious adjustments and in watching chips being made. Consequently, to reduce or eliminate the amount of skilled labor that is required, turret lathes, screw machines, and other types of semiautomatic and automatic lathes have been highly developed and are widely used in manufacturing. 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 w here smaller quantities rather than large production runs are encountered. The engine lathe has been replaced in today39。 s production shops by a wide variety of automatic lathes such as automatic tracer lathes, turret lathes, and automatic screw machines. All the advantages of singlepoint tooling for maximum metal removal, and the use of form tools for finish and accuracy, are now at the designer39。 s fingertips with production speeds 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 tole rances 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. Production machining equipment must be evaluated now, more than ever before, in terms of ability to repeat accurately andrapidly. 9 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 achievi。