【導讀】車床主要是為了進行車外圓、車端面和鏜孔等項工作而設計的機床。車削很少在其他種類的機床上進行，而且任何一種其他機床都不能像車床那樣方便地進行車削加工。由于車床還可以用來鉆孔和鉸孔，車床的多功能性可以使工件在一次安裝中完成幾種加工。因此，在生產(chǎn)中使用的各種車床比任何其他種類的機床都多。車床的基本部件有：床身、主軸箱組件、尾座組件、溜板組件、絲杠和光杠。床身是車床的基礎件。它能常是由經(jīng)過充分正火或時效處理的灰鑄鐵或者球墨鐵制成。通常在床身上有內(nèi)外兩組平行的導軌。為了抵抗磨損和擦傷，大多數(shù)現(xiàn)代機床的導軌是經(jīng)過表面淬硬的，但是在操作時還應該小心，以避免損傷導軌。導軌上的任何誤差，常常意味著整個機床的精度遭到破壞。尾座組件主要由三部分組成。尾座的第三個組成部分是尾座套筒。對于一臺數(shù)控機床，其上必須安有一個被稱為閱讀機的界面裝置，用來接受和解譯出編程指令。

　　

【正文】 he gear with the larger helix angle should be used as the driver if both gears have the same hand.Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they pletely wrap around the pitch cylinder they are called threads. Its mating gear is called a worm gear, which is not a true helical gear. A worm and worm gear are used to provide a high angularvelocity reduction between nonintersecting shafts which are usually at right angle. The worm gear is not a helical gear because its face is made concave to fit the curvature of the worm in order to provide line contact instead of point contact. However, a disadvantage of worm gearing is the high sliding velocities across the teeth, the same as with crossed helical gears.Worm gearing are either single or double enveloping. A singleenveloping gearing is one in which the gear wraps around or partially encloses the worm.. A gearing in which each element partially encloses the other is, of course, a doubleenveloping worm gearing. The important difference between the two is that area contact exists between the teeth of doubleenveloping gears while only line contact between those of singleenveloping gears. The worm and worm gear of a set have the same hand of helix as for crossed helical gears, but the helix angles are usually quite different. The helix angle on the worm is generally quite large, and that on the gear very small. Because of this, it is usual to specify the lead angle on the worm, which is the plement of the worm helix angle, and the helix angle on the gear。 the two angles are equal for a 90deg. Shaft angle.When gears are to be used to transmit motion between intersecting shaft, some of bevel gear is required. Although bevel gear are usually made for a shaft angle of 90 deg. They may be produced for almost any shaft angle. The teeth may be cast, milled, or generated. Only the generated teeth may be classed as accurate. In a typical bevel gear mounting, one of the gear is often mounted outboard of the bearing. This means that shaft deflection can be more pronounced and have a greater effect on the contact of teeth. Another difficulty, which occurs in predicting the stress in bevelgear teeth, is the fact the teeth are tapered. Straight bevel gears are easy to design and simple to manufacture and give very good results in service if they are mounted accurately and positively. As in the case of squr gears, however, they bee noisy at higher values of the pitchline velocity. In these cases it is often good design practice to go to the spiral bevel gear, which is the bevel counterpart of the helical gear. As in the case of helical gears, spiral bevel gears give a much smoother tooth action than straight bevel gears, and hence are useful where high speed are encountered.It is frequently desirable, as in the case of automotive differential applications, to have gearing similar to bevel gears but with the shaft offset. Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution. The tooth action between such gears is a bination of rolling and sliding along a straight line and has much in mon with that of worm gears.A shaft is a rotating or stationary member, usually of circular cross section, having mounted upon it such elementsas gears, pulleys, flywheels, cranks, sprockets, and other powertransmission elements. Shaft may be subjected to bending, tension, pression, or torsional loads, acting singly or in bination with one another. When they are bined, one may expect to find both static and fatigue strength to be important design considerations, since a single shaft may be subjected to static stresses, pletely reversed, and repeated stresses, all acting at the same time.The word “shaft” covers numerous variations, such as axles and spindles. Anaxle is a shaft, wither stationary or rotating, nor subjected to torsion load. A shirt rotating shaft is often called a spindle.When either the lateral or the torsional deflection of a shaft must be held to close limits, the shaft must be sized on the basis of deflection before analyzing the stresses. The reason for this is that, if the shaft is made stiff enough so that the deflection is not too large, it is probable that the resulting stresses will be safe. But by no means should the designer assume that they are safe。 it is almost always necessary to calculate them so that he knows they are within acceptable limits. Whenever possible, the powertransmission elements, such as gears or pullets, should be located close to the supporting bearings, This reduces the bending moment, and hence the deflection and bending stress.Although the von MisesHenckyGoodman method is difficult to use in design of shaft, it probably es closest to predicting actual failure. Thus it is a good way of checking a shaft that has already been designed or of discovering why a particular shaft has failed in service. Furthermore, there are a considerable number of shaftdesign problems in which the dimension are pretty well limited by other considerations, such as rigidity, and it is only necessary for the designer to discover something about the fillet sizes, heattreatment, and surface finish and whether or not shot peening is necessary in order to achieve the required life and reliability.Because of the similarity of their functions, clutches and brakes are treated together. In a simplified dynamic representation of a friction clutch, or brake, two inertias I1 and I2 traveling at the respective angular velocities W1 and W2, one of which may be zero in the case of brake, are to be brought to the same speed by engaging the clutch or brake. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation, resulting in a temperature rise. In analyzing the performance of these devices we shall be interested in the actuating force, the torque transmitt