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1、外文翻译LATHES AND GRINDINGLathes are machine tools designed primarily to do turning, facing and boring. Very little turning is done on other types of machine tools, and none can do it with equal facility. Because lathe also can do drilling and reaming, their versatility permits several operations to be
2、 done with a single setup of the workpiece. The accounts for the fact that lathes of various types are more widely used in manufacturing than any other machine tool.Lathes in various forms have existed for more than two thousand years. Modern lathes date form about 1797, when Henry Maudsley develope
3、d one with a leadscrew. It provided controlled, mechanical feed of the tool. This ingenious Englishman also developed a change-gear system that could connect the motion of the spindle and leadscrew and thus enable threads to be cut.Lathe Construction. The essential components of a lathe are the bed,
4、 headstock assembly, tailstock assembly, carriage assembly, quick-change gear box, and the leadscrew and feed rod.The bed is the backbone of a lathe. It usually is made of well-normalized or aged gray or nodular cast iron and provides a heavy, rigid frame on which all the other basic components are
5、mounted. Two sets of parallel, longitudinal way, inner and outer, are contained on the bed, usually on the upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one flat way in one or both sets. Because several other components are mounted and/o
6、r move on the ways they must be made with precision to accuracy of alignment. Similarly, proper precaution should be taken in operating a lathe to assure that the ways are not damaged. Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed. The ways on most modern la
7、thes are surface hardened to offer greater resistance to wear and abrasion.The headstock is mounted in a fixed position on the inner ways at one end of the lathe bed. It provides a powered means of rotating the work at various speeds. It consists, essentially, of a hollow spindle, mounted in accurat
8、e bearings, and a set of transmission gearsimilar to a truck transmissionthrough which the spindle can be rotated at a number of speeds. Most lathes provide from eight to eighteen speeds, usually in a geometric ratio, and modern lathes all the speeds can be obtained merely by from two to four levers
9、. An increasing trend is to provide to continuously variable speed range through electrical or mechanical drives.Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball tapes. A longitudi
10、nal hole extends through the spindle so that long bar stock can be fed through it. The size of this hole is an important size dimension of a lathe because it determines the maximum size of bar stock that can be machined when the material must be fed through the spindle.The inner end of the spindle p
11、rotrudes from the gear box and contains a means for mounting various types of chucks, face plates, and dog plates on it. Whereas small lathes often employ a threaded section to which the chucks are screwed, most large lathes utilize either cam-lock or key-drive taper noses. These provide a large-dia
12、meter taper than assures the accurate alignment of the chuck, and a mechanism that permits the chuck or face plate to be locked or unlocked in position without the necessity of having to rotate these heavy attachments.Power is supplied to the spindle by means of an electric motor through a V-belt or
13、 silent-chain drive. Most modern lathes have motors of from 5 to 15 horsepower to provide adequate power for carbide and ceramic tools at their high cutting speeds.The tailstock assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudin
14、ally thereon, with a means for clamping the entire assembly in any desired location. An upper casting fits on the lower one and can be moved transversely upon it on type of keyed ways. This transverse motion permits aligning the tailstock and headstock spindles and provides a method of turning taper
15、s. The third major component of the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 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 open end of the quill hole terminates
16、in a Morse taper in which a lathe center, or various tools as drills, can be held. A graduated scale, several inches in length, usually is engraved on the outside of the quill to aid in controlling its motion in and out of the upper casting. A locking device permits clamping the quill in any desired position.The carriage assembly provides the means for mounting and moving cutting tools. The carriage is a relatively flat H-shaped casting that rests and moves on the out
