【正文】 ks, 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 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 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 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 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 handwheel 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 a base, 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 forth and controlled by means of a short lead screw operated by a handwheel and a calibrated dial. Manual and powered motion 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 handwheel on the front of the apron, which is geared to a pinion on the back side. This 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 throughout most of its length, passes through the two reversing bevel pinions and is keyed to them. Either pinion can be brought into mesh with a mating bevel gear by means of the reversing lever on the front of the apron and thus provide “forward” or “reverse” power to the carriage. Suitable clutches connect either the rack pinion or the crossslide screw to provide longitudinal motion of the carriage or transverse motion of cross slide. For cutting threads, a second means of longitudinal drive is provided by a lead screw. Whereas motion of the carriage when driven by the feedrod mechanism takes place through a friction clutch in which slippage is possible, motion through the lead screw is by a direct, mechanical connection between the apron and the lead screw. This is achieved by a split nut. By means of a clamping lever on the front of the apron, the split nut can be closed around the lead screw. With the split nut closed, the carriage is moved along the lead screw by direct drive without possibility of slippage. Modern lathes have a quickchange gear box. The input end of this gear box is driven from the lathe spindle by means of suitable gearing. The output end of the gear box is connected to the feed rod and lead screw. Thus, through this gear train, leading from the spindle to the quickchange gear box, thence to the lead scr