機(jī)械設(shè)計(jì)外文翻譯--車床和銑床-機(jī)械設(shè)計(jì)-文庫吧資料
2025-01-27 06:03本頁面
【正文】 . Similarly， proper precaution should betaken 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 lathes 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 accurate bearings， and a set of transmission gears——similar to a truck transmission——through 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 on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a 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 types. A long itudinal 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 protrudes 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 camlock or keydrive taper noses. These provide a largediameter taper that 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 Vbelt or silentchain drive. Most modern lathes have motors of from 5 to15 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 longitudinally 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 some type of keyed ways. This transverse motion permits aligning the tailstock and headstock spindles and provides a method of turning tapers. The third major ponent of the assembly is the tailstock quill. This is a hollow steel cylinder， usually about2 to3 inches in diameter， that can be moved several inches longitudinally in and out of the upper casting by means of a hand wheel and screw. The open end of the quill hole terminates in a Morse taper in which a lathe center， or various tools such 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 Hshaped casting that rests and moves on the outer set of ways on the bed. The transverse bar of the carriage contains ways on which the cross slide is mounted and can be moved by means of a feed screw that is controlled by a small hand wheel and a graduated dial. Through the cross slide a means is provided for moving the lathe tool in the direction normal to the axis of rotation of the work. On most lathes the tool post actually is mounted on a pound rest. This consists of abase， which is mounted on the cross slide so that it can be pivoted about a vertical axis， and an upper casting. The upper casting is mounted on ways on this base so that it can be moved back and fort
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