机电英语 (3)

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The lathe is a machine that removes material by rotating the work against a cutter. Parts to be machined can be held between centers, attached to a face plate, supported in a jaw chuck, or held in a draw-in chuck or collet.
Part3 Processing Machine
Unit 1Engine Lathe Unit 2The Non-Traditional Machining Hand-book Unit 3Primary Processes
Unit 1Engine Lathe
Reading Target 1．Illustrate principal parts of an engine lathe and introduce their function. 2．Make you know several methods to hold and move workpieces on the lathe.
The tailstock spindle is a hollow shaft that is mounted in the tailstock body. The left end of the hole is tapered to hold the tailstock or dead center to hold twist drills, etc. , for doing work as mentioned above.
Headstock
The headstock of a lathe is a subassembly that is mounted on the inner ways at the left end of the bed. On a geared-head lathe, the headstock casting supports and encloses a train of gearsspindle at rpm[2] which are suited to the operating conditions of the different jobs routed to the machine.
Compound Rest
The compound rest is a casting that is mounted on a circular bearing surface on top of the cross slide. It has a swivel base, graduated in degrees, which allows it to be set so that a cutting tool may be fed at angles other than 90 deg to the axis of the lathe[6]. This motion of a tool will generate a conical surface.
Tailstock
The tailstock is a subassembly that is mounted on the inner ways, at the right end of the bed, to align it with the headstock.
It is adjustable on the bed longitudinally so that it may be positioned wherever needed to support workpieces that are held on centers and to hold twist drills, reamers, and other tools that may be used to perform operations on jobs that are held with a chuck or on the large faceplate.
Levers at the front of the headstock casting are employed to shift the gears into trains that will give the cutting speeds required.
The headstock or live spindle is the final shaft in the power transmission system. It supports and rotates workpieces about the axis of the lathe, that is, about the horizontal line which is fixed by the center line of the headstock spindle[3].
Saddle
The saddle is an H-shaped casting that forms a bridge across the top of the bed. It rests on the outer ways of the machine. Since the ways are parallel to the axis of the lathe, longitudinal motion of the carriage on them will guide a turning or boring tool parallel to that axis. This motion of a cutting tool past work that rotates about the axis will generate a cylinder.
Work held in this manner can likewise be centered, drilled, bored, or reamed. In addition, the lathe can be used for cutting threads and turning tapers; with the proper attachment, it can be adapted to simple milling or grinding operations. It is probably the oldest of all the machine tools as well as the most important machine in modern production. Fig3.1.1 illustrates principal of an engine lathe.
The headstock spindle is hollow to give it stiffness, and the hole is tapered at the nose end to receive the headstock or live center. The outside of the spindle nose is finished to a standard shape and size to receive the faceplates and chucks that are used to hold and drive workpieces.
Legs under the bed raise it so that the top is at a convenient working height above the floor. A chip pan under the bed collects chips and cutting fluid when one is used[1].
The tailstock is made of two principal castings——a base and a body. The construction is such that the body may be adjusted transversely on the base to offset the tailstock center with respect to the lathe's axis to perform taper-turning operations on workpicces, which are held on centers[4].
Micrometer Dials
The cross-feed screw and the compound rest-feed screw have micrometer dials on them that may be used to set a turning or boring tool so that it will take a cut to known thousandth of an inch for sizing a workpiece accurately.
Principal Parts of an Engine Lathe
Bed
The main casting of an engine lathe is a horizontal member called a "bed". Planed surfaces on top of the bed, called "ways" or "vees", align the headstock and tailstock and guide the carriage so that it moves longitudinally parallel to the axis of the machine.
Carriage
The lathe's carriage is a subassembly that is mounted on the outer ways of the machine between the headstock and tailstock. Its function is to hold and move the turning and boring tools that are used on the machine. The principal parts of the carriage are a saddle, cross slide, compound rest, tool post and apron.
Though this machine is particularly adapted to cylindrical work, it may also be used for many other purposes. Plain surfaces can be obtained by supporting the work on a face plate or in a chuck.
Cross Slide
The cross slide is a casting that is mounted on the bridge of the saddle in a bearing[5], which is machined at 90 deg to the axis of the lathe. Transverse motion of the cross slide on the saddle, therefore, guides a cutting tool at 90 deg to the axis in a motion that will generate a plane surface.