【正文】 cle. One singlepoint cutting tool is used. Straight, tapered, and contoured turned or faced surfaces and bored holes are repetitively produced by the motion of a stylus as it follows the outline of a lowcost template. The template is generally mounted at the rear of the machine. The movements of the stylus are actuated by mechanical, air, hydraulic, or electrical methods. Work may be held between centers or chucked. Duplicating or tracer attachments are generally factoryinstalled on a standard engine lathe, although special machines are also available. Turret Lathe: Turret lathes are semiautomatic machine tools which can produce parts in greater quantities, to closer tolerances, faster, and as a result more economically than is possible by conventional engine lathes. Unlike the engine lathe, the turret lathe is not restricted to a single cutting tool. A leading advantage is that several operations may be performed on a work pace at a given time. It should be noted, however, that the range and types of turret lathe operations are essentially the same as those associated with the engine lathe.FIGURE 166 Turret lathe production part (Courtesy, Jones Lamson) Figure 166 illustrates examples of turret lathe production parts. To offset the need for frequent tool changes, a sixsided turret is used in place of a tailstock. The turret may easily be indexed so that any desired cutting tool may contact the work piece. Additional cutting tools may be placed in square turrets on the cross slide and may be readily indexed to machine other surfaces. Unlike a cutting tool used on an engine lathe, once turret lathe tools have been properly inserted in one of the various tooling stations, they need not be remove until they require sharpening or after the production run has been pleted. Finally, there is also available a single tool holder on a turret lathe which is mounted with a cutting tool on the rear of the cross slide. Full advantage of the versatility and adaptability of the engine lathe can be obtained only in cases where the services of a highly skilled machinist are available. Skilled labor is expensive. Parts produced by engine lathe operations are usually more costly than similar parts produced on a turret lathe. Turret lathe production costs are often minimized by using skilled setup men whose job it is to set and adjust the tools, leaving the simple and repetitive operations for the lowerpayscale machine operators.FIGURE 167 Ramtype universal turret lathe( Courtesy, Jones Lamson) Turret lathes may be classified as horizontal and vertical. The two leading types of horizontal turret lathes are ram type, shown in Figure 167, and the saddle type. Both types are suited to bar(cylindrical turning) and chucking work. The ramtype turret lathe is best suited for light bar work and small chucking jobs, while the saddletype turret lathe is primarily used for longer bar work and for heavier chucking work pieces. Figure 168 shows a numerically controlled fouraxis turret lathe. Ideal for bar and chucking work, they can also handle betweencenters shaft work.FIGURE 168 A fouraxis numerically controlled turret lathe( Courtesy, Giddings LewisBickford Machine Compangy) Vertical turret lathes are designed for considerably larger and heavier work than is monly associated with either type of horizontal turret lathes. Vertical machines are utilized solely for plex chucking work, particularly for boring operations, and are not adapted to bar work. An example of a vertical turret is shown in Figure 169. FIGURE169 A vertical turret lathe with a 36 in. diameter table (Courtesy, The Bullard Company)HighProduction Lathes It is difficult to precisely classify the various types of turning machines strictly according to their production output, Machines previously discussed are all reasonably similar, in that each type requires operator attention to an extent that varies form “considerable” to “only occasional.” The types of highproduction lathes selected for following discussion are those that run almost continuously. Sones are fully automatic and require only occasional operator attention. Automatics Screw Machines: Automatic screw machines (or automatic bar machines) were originally designed for the high production of screws and various other threaded fasteners. The basic beginnings of this machine date back to the 1880s, when the first machine was developed. The machine is essentially an advanced form of a turret lathe which fashions a wide range of parts is large quantities form bar stock. High output of intricate mechanisms designed to automatically feed single and continuous lengths of stock, index the turret for the desired sequence of the proper cutting tools, and retract the tool after cutting. Contrary to the designation “screw machine,” production is not limited to threaded parts. The process is adaptable to the economical production of turned and formed parts of almost unlimited configuration, as shown in Figure 1610.FIGURE 1610 Typical Brown Sharp produced on a screw machine ( Courtesy, e Manufacturing Co.)parts FIGURE 1611 A single spindle screw machine (Courtesy. Brown Sharpe Manufacturing Co.)FIGURE 1612 A closeup view of cutting tools in a sixstation turret ( Courtesy, Brown Sharpe Manufacturing Co.) A automatic screw machines may be classified as singlespindle automatics，multiplespindle automatics, and automatic chucking machines. An example of a singlespindle bar automatic screw machine is shown in Figure 1611. Bar stock (ranging from round, square , hexagonal, or other crosssectional shapes) is fed through a revolving hollow spindle at the beginning of each cycle of operation. The stock is stopped at a predetermined distance and held during the cutting operations in a cullet. Cutting tools are mounted around a sixstation turret shown in Figure 1612, which rotates in a vertical plane in a Ferris wheel