1、附录 1 LATHES & MILLING A shop that is equipped with a milling machine and an engine lathe can machine almost any type of product of suitable size. The basic machines that are designed primarily to do turning， facing and boring are called lathes. Very little turning is done on other types of machine t
2、ools， and none can do it with equal facility. Because lathe can do boring， facing， drilling， and reaming in addition to turning， their versatility permits several operations to be performed with a single setup of the workpiece. This accounts for the fact that lathes of various types are more widely
3、used in manufacturing than any other machine tool. Lathes in various forms have existed for more than two thousand years. Modern lathes date from about 1797， when Henry Maudsley developed one with a leads crew. It provided controlled， mechanical feed of the tool. This ingenious Englishman also devel
4、oped a change gear system that could connect the motions of the spindle and leadscrew and thus enable threads to be cut. Lathe Construction. The essential components of a lathe are depicted in the block diagram of picture. These are the bed， headstock assembly， tailstock assembly，carriage assembly，
5、quick-change gearbox， and the leadscrew and feed rod. The bed is the back bone 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 mounted. Two sets of parallel， longitudinal ways， inner and
6、 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/or move on the ways they must be made with precision to ass
7、ure accuracy of alignment. 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 resistanc
8、e 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 gearssimilar
9、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 on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a co
10、ntinuously 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 s
11、o 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 contai
12、ns 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-diameter taper that assures the accurate
13、 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 silent-chain drive. Most modern lat
14、hes 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 clamp
15、ing 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 component of
16、 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 lath
17、e 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 asse
18、mbly provides the means for mounting and moving cutting tools. The carriage is a relatively flat H-shaped 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 t
19、hat 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 compound rest. This consists of abase， which is mount
20、ed 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 forth and controlled by means of a short lead screw operated by a hand wheel and a calibrated dial. Manual and powered motio
21、n for the carriage， and powered motion for the cross slide， is provided by mechanisms within the apron， attached to the front of the carriage. Manual movement of the carriage along the bed is effected by turning a hand wheel on the front of the apron， which is geared to a pinion on the back side. Th
22、is pinion engages a rack that is attached beneath the upper front edge of the bed in an inverted position. To impart powered movement to the carriage and cross slide， a rotating feed rod is provided. The feed rod， which contains a keyway through out most of its length，passes through the two reversing bevel pinions and is keyed to them . Either pinion cam be brought into mesh with a
