车床及其结构外文翻译.doc

the lathe and its construction(原文)from mechanical engineering englisha lathe is a machine tool used primarily for producing surfaces of revolution and flat edges.based on their purpose, construction, number of tools that can simultaneously be mounted, and degree of automation, lathes-or, more accurately, lathe-type machine tools can be classified as follows:(1)engine lathes(2)toolroom lathes(3)turret lathes(4)vertical turning and boring mills(5)automatic lathes(6)special-purposelathes in spite of that diversity of lathe-type machine tools, they all have common features with respect to construction and principle of operation. these features can best be illustrated by considering the commonly used representative type, the engine lathe. following is a description of each of the main elements of an engine lathe, which is shown in fig.11.1. lathe bed. the lathe bed is the main frame, involving a horizontal beam on two vertical supports. it is usually made of grey or nodular cast iron to damp vibrations and is made by casting. it has guideways to allow the carriage to slide easily lengthwise. the height of the lathe bed should be appropriate to enable the technician to do his or her job easily and comfortably. headstock. the headstock is fixed at the left hand side of the lathe bed and includes the spindle whose axis is parallel to the guideways (the slide surface of the bed). the spindle is driven through the gearbox, which is housed within the headstock. the function of the gearbox is to provide a number of different spindle speeds (usually 6 up to 18 speeds). some modern lathes have headstocks with infinitely variable spindle speeds, which employ frictional ,electrical ,or hydraulic drives. the spindle is always hollow, i. e., it has a through hole extending lengthwise. bar stocks can be fed through that hole if continuous production is adopted. also, that hole has a tapered surface to allow mounting a plain lathe center. the outer surface of the spindle is threaded to allow mounting of a chuck, a face plate, or the like. tailstock. the tailstock assembly consists basically of three parts, its lower base, an intermediate part, and the quill. the lower base is a casting that can slide on the lathe bed along the guideways, and it has a clamping device to enable locking the entire tailstock at any desired location, depending upon the length of the workpiece. the intermediate part is a casting that can be moved transversely to enable alignment of the axis of the tailstock with that of the headstock. the third part, the quill, is a hardened steel tube, which can be moved longitudinally in and out of the intermediate part as required. this is achieved through the use of a handwheel and a screw, around which a nut fixed to the quill is engaged. the hole in the open side of the quill is tapered to enable mounting of lathe centers or other tools like twist drills or boring bars. the quill can be locked at any point along its travel path by means of a clamping device. the carriage. the main function of the carriage is mounting of the cutting tools and generating longitudinal and/or cross feeds. it is actually an h-shaped block that slides on the lathe bed between the headstock and tailstock while being guided by the v-shaped guideways of the bed. the carriage can be moved either manually or mechanically by means of the apron and either the feed rod or the lead screw.when cutting screw threads, power is provided to the gearbox of the apron by the lead screw. in all other turning operations, it is the feed rod that drives the carriage. the lead screw goes through a pair of half nuts, which are fixed to the rear of the apron.when actuating a certain lever, the half nuts are clamped together and engage with the rotating lead screw as a single nut, which is fed, together with the carriage, along the bed. when the lever is disengaged, the half nuts are released and the carriage stops.on the other hand, when the feed rod is used, it supplies power to the apron through a worm gear. the latter is keyed to the feed rod and travels with the apron along the feed rod, which has a keyway extending to cover its whole length.a modern lathe usually has a quick-change gearbox located under the headstock and driven from the spindle through a train of gears. it is connected to both the feed rod and the lead screw and enables selecting a variety of feeds easily and rapidly by simply shifting the appropriate levers. the quick-change gearbox is employed in plain turning, facing and thread cutting operations. since that gearbox is linked to the spindle, the distance that the apron (and the cuttingtool) travels for each revolution of the spindle can be controlled and is referred to as the feed. lathe cutting tools the shape and geometry of the lathe tools depend upon the purpose for which they are employed.turning tools can be classified into two main groups, namely, external cutting tools and internal cutting tools. each of these two groups include the following types of tools: turning tools. turning tools can be either finishing or rough turning tools. rough turning tools have small nose radii and are employed when deep cuts are made. on the other hand, finishing tools have larger nose radii and are used for obtaining the final required dimensions with good surface finish by making slight depths of cut. rough turning tools can be right-hand or left-hand types, depending upon the direction of feed. they can have straight, bent, or offset shanks. facing tools. facing tools are employed in facing operations for machining plane side or end surfaces. there are tools for machining left-hand-side surfaces and tools for right-hand-side surfaces. those side surfaces are generated through the use of the cross feed, contrary to turning operations, where the usual longitudinal feed is used. cutoff tools. cutoff tools, which are sometimes called parting tools, serve to separate the workpiece into parts and/or machine external annular grooves. thread-cutting tools. thread-cutting tools have either triangular, square, or trapezoidal cutting edges, depending upon the cross section of the desired thread. also, the plane angles of these tools must always be identical to those of the thread forms. thread-cutting tools have straight shanks for external thread cutting and are of the bent-shank type when cutting internal threads. form tools. form tools have edges especially manufactured to take a certain form, which is opposite to the desired shape of the machined workpiece.an hss tool is usually made in the form of a single piece, contrary to cemented carbides or ceramic, which are made in the form of tips. the latter are brazed or mechanically fastened to steel shanksfig.11.2 indicates an arrangement of this latter type, which includes the carbide tip, the chip breaker, the pad, the clamping screw (with a washer and a nut), and the shank.as the name suggests, the function of the chip breaker is to break long chips every now and then, thus preventing the formation of very long twisted ribbons that may cause problems during the machining operation. the carbide tips (or ceramic tips) can have different shapes, depending upon the machining operations for which they are to be employed. the tips can either be solid or with a central through hole, depending on whether brazing or mechanical clamping is employed for mounting the tip on the shank. 车床及其结构（译文）车床是主要用于生成旋转表面和平整边缘的机床。根据它们的使用目的、结构、能同时被安装刀具的数量和自动化的程度，车床或更确切地说是车床类的机床，可以被分成以下几类： 1.普通车床2.万能车床3.转塔车床4.立式车床5.自动车床6.特殊车床 虽然车床类的机床多种多样，但它们在结构和操作原理上具有共同特性。这些特性可以通过普通车床这一最常用的代表性类型来最好地说明。下面是关于图11.1所示普通车床的主要部分的描述。 车床床身：车床床身是包含了在两个垂直支柱上水平横梁的主骨架。为减振它一般由灰铸铁或球墨铸铁铸造而成。它上面有能让大拖板轻易纵向滑动的导轨。车床床身的高度应适当以让技师容易而舒适地工作。 主轴箱：主轴箱固定在车床床身的左侧，它包括轴线平行于导轨的主轴。主轴通过装在主轴箱内的齿轮箱驱动。齿轮箱的功能是给主轴提供若干不同的速度(通常是6到18速)。有些现代车床具有采用摩擦、电力或液压驱动的无级调速主轴箱。 主轴往往是中空的，即纵向有一通孔。如果采取连续生产，棒料能通过此孔进给。同时，此孔为锥形表面可以安装普通车床顶尖。主轴外表面是螺纹可以安装卡盘、花盘或类似的装置。 尾架：尾架总成基本包括三部分，底座、尾架体和套筒轴。底座是能在车床床身上沿导轨滑动的铸件，它有一定位装置能让整个尾架根据工件长度锁定在任何需要位置。尾架体为一能横向运动的铸件，它可以调整尾架轴线与主轴箱轴线成一直线。第三部分，套筒轴是一淬硬钢管，它能根据需要在尾架体中纵向进出移动。这通过使用手轮和螺杆来达到，与螺杆啮合的是一固接在套筒轴上的螺母。套筒轴开口端的孔是锥形的，能安装车床顶尖或诸如麻花钻和镗杆之类的工具。套筒轴通过定位装置能沿着它的移动路径被锁定在任何点。 大拖板：大拖板的主要功能是安装刀具和产生纵向和/或横向进给。它实际上是一由车床床身v形导轨引导的、能在车床床身主轴箱和尾架之间滑动的h形滑块。大拖板能手动或者通过溜板箱和光杆(进给杆)或丝杆(引导螺杆)机动。 在切削螺旋时，动力通过丝杆提供给溜板箱上的齿轮箱。在其余车削作业中，都由光杆驱动大拖板。丝杆穿过一对固定在溜板箱后部的剖分螺母。当开动特定操作杆时，剖分螺母夹在一起作为单个螺母与旋转的丝杆啮合，并带动拖板沿着床身提供进给。当操作杆脱