The lathe is mainly a machine tool designed for the work of turning the outer circle, turning the end face and boring. Turning is rarely performed on other kinds of machine tools, and no other kind of machine tool can perform turning operations as easily as lathes. Since the lathe can also be used for drilling and reaming, the versatility of the lathe allows the workpiece to undergo several operations in one setup. As a result, more lathes of all kinds are used in production than any other kind of machine tool.
The basic components of a lathe are: bed, headstock assembly, tailstock assembly, slide plate assembly, lead screw and feed rod.
(1) The bed is the basic part of the lathe. It can often be made of fully normalized or aged gray or ductile iron. It is a solid rigid frame on which all other essential components are mounted on the bed. Usually there are two sets of parallel guide rails inside and outside on the bed. Some manufacturers use triangular rails with the tips of the rails pointing upwards (mountain rails) for all four rails, while others use one triangular rail and one rectangular rail in one or two sets. The guide rails are precision machined to ensure their straightness accuracy. The guideways of most modern machine tools are case hardened to resist wear and galling, but care should also be taken to avoid damaging the guideways during handling. Any error in the guideway often means that the accuracy of the entire machine tool is destroyed.
(2) The headstock is installed at a fixed position on the inner guide rail, generally at the left end of the bed. It provides power and allows the workpiece to rotate at various speeds. It basically consists of a hollow main shaft mounted in precision bearings and a series of transmission gears (similar to a truck gearbox). Through variable speed gears, the main shaft can rotate at many speeds. Most lathes have 8 to 12 speeds, generally arranged in proportional series. Moreover, on modern machine tools, only 2 to 4 handles are needed to get the full speed. A growing trend is for continuously variable transmissions by electrical or mechanical means. Since the accuracy of the machine tool depends to a large extent on the spindle, the spindle has a large structural size and is usually mounted in preloaded heavy-duty tapered roller bearings or ball bearings. A through hole runs the full length of the spindle through which long bar stock can be fed. The size of the spindle hole is an important dimension of the lathe, so when the workpiece must be fed through the spindle hole, it determines the maximum size of the bar stock that can be machined.
(3) The tailstock assembly is mainly composed of three parts. The bottom plate cooperates with the inner guide rail of the bed and can move longitudinally on the guide rail. There is a device on the bottom plate that can clamp the entire tailstock assembly in any position. The tailstock body is mounted on the base plate and can be moved laterally on the base plate along some type of keyway to align the tailstock with the spindle in the headstock. The third component of the tailstock is the tailstock sleeve. It is a hollow cylinder of steel, usually about 51 to 76 mm (2 to 3 inches) in diameter. The tailstock quill can be moved longitudinally in and out of the tailstock body several inches by means of a handwheel and screw; lathe specifications are indicated by two dimensions. The first is called the maximum machining diameter on the bed of the lathe. This is for a workpiece that can be rotated on a lathe
The maximum diameter. It is approximately twice the distance between the line connecting the two tops and the closest point on the rail. The second specification dimension is the maximum distance between two tips. The maximum machining diameter on the lathe bed indicates the maximum diameter of the workpiece that can be turned on the lathe, and the maximum distance between the two centers indicates the maximum length of the workpiece that can be installed between the two centers.
Ordinary lathes are the most frequently used type of lathes in production. They are heavy-duty machines with all those parts previously described, and with the exception of the small tool holders, all tool movements have motorized feeds. Their specifications are usually: the maximum machining diameter on the lathe bed is 305~610mm (12~24 inches); however, lathes with a maximum machining diameter of 1270mm (50 inches) on the bed and a distance between the two centers of 3658mm are not available. Not uncommon. Most of these lathes have chip trays and an internally mounted coolant circulation system. Small ordinary lathes—the maximum machining diameter of the lathe surface generally does not exceed 330mm (13 inches)—are designed as desktop lathes, and their bed is installed on a workbench or cabinet. Although ordinary lathes have many uses and are very useful machine tools, but Changing and adjusting tools and measuring workpieces takes a lot of time, so they are not suitable for high-volume production applications. Typically, their actual machining time is less than 30% of their total machining time. In addition, skilled workers are required to operate general lathes, which are highly paid and difficult to find. However, most of the operator’s time is spent on simple repeated adjustments and observing the chip cutting process. Therefore, in order to reduce or completely eliminate the employment of such skilled workers, hexagonal lathes, threading lathes and other types of semi-automatic and automatic lathes have been well developed and have been widely used in production.
