機(jī)械設(shè)計(jì)外文翻譯--車(chē)床和銑床-機(jī)械設(shè)計(jì)-展示頁(yè)
2025-01-31 06:03本頁(yè)面
【正文】 h and controlled by means of a short lead screw operated by a hand wheel 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 hand wheel 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 through out most of its length，passes through the two reversing bevel pinions and is keyed to them . Either pinion cam 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 gearbox is driven from the lathe spindle by means of suitable gearing. The out put 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 gearbox， thence to the lead screw and feed rod， and then to the carriage， the cutting tool can be made to move a specific distance， either longitudinally or transversely， for each revolution of the spindle. A typical lathe provides， through the feed rod， fortyeight feeds ranging from inch inch per revolution of the spindle， and， through the lead screw， leads for cutting fortyeight different threads from to some older and some cheaper lathes， one or two gears in the gear train between the spindle and the change gear box must be changed in order to obtain a full range of threads and feeds. Milling is a basic machining process in which the surface is generated by the progressive formation and removal of chips of material from the workpiece as it is fed to a rotating cutter in a direction perpendicular to the axis of the cutter. .In some cases the workpiece is stationary and the cutter is fed to the work. In most instances a multipletooth cutter is used so that the metal removal rate is high， and frequently the desired surface is obtained in a single pass of the work. The tool used in milling is known as a milling cutter. It usually consists of a cylindrical body which rotates on its axis and contains equally spaced peripheral teeth that intermittently engage and cut the workpiece. In some cases the teeth extend part way across one or both ends of the cylinder. Because the milling principle provides rapid metal removal and can produce good surface finish， it is particularly wellsuited for massproduction work， and excellent milling machines have been developed for this purpose. However， very accurate and versatile milling machines of a generalpurpose nature also have been developed that are widely used in jobshop and tool and die work. A shop that is equipped with a milling machine and an engine lathe can machine almost any type of product of suitable size. Types of Milling Operations. Milling operations can be classified into two broad categories， each of which has several variations： peripheral milling a surface is generate
試題試卷相關(guān)推薦
鄂ICP備17016276號(hào)-1