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Mechanical engineering |Машиностроение

Lesson 9

Read the text: A lathe

 A lathe is a machine tool which spins a block of material to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the work piece to create an object which has symmetry about an axis of rotation. Lathes are used in woodturning, metalworking, metal spinning, and glass working. Most suitably equipped metalworking lathes can also be used to produce most solids of revolution, plane surfaces and screw threads or helices. Lathes that sit on a bench or table are called "bench lathes". Lathes that do not have additional integral features for repetitive production, but rather are used for individual part production or modification as the primary role, are called "engine lathes". Lathes with a very large spindle bore and a chuck on both ends of the spindle are called "oil field lathes". Fully automatic mechanical lathes, employing cams and gear trains for controlled movement, are called screw machines. Lathes that are controlled by a computer are CNC lathes. Lathes with the spindle mounted in a vertical configuration, instead of horizontal configuration, are called vertical lathes or vertical boring machines. They are used where very large diameters must be turned, and the work piece (comparatively) is not very long. Lathes with a cylindrical tailstock that can rotate around a vertical axis, so as to present different facets towards the headstock (and the work piece) are turret lathes. A lathe equipped with indexing plates, profile cutters, spiral or helical guides, etc., so as to enable ornamental turning is an ornamental lathe. Various combinations are possible: e.g. one could have a vertical CNC lathe (such as a CNC VTL), etc. Lathes can be combined with other machine tools, such as a drill press or vertical milling machine. These are usually referred to as combination lathes. In a metalworking lathe, metal is removed from the work piece using a hardened cutting tool, which is usually fixed to a solid moveable mounting called the "tool post", which is then moved against the work piece using hand wheels and/or computer controlled motors. These (cutting) tools come in a wide range of sizes and shapes depending upon their application. Some common styles are diamond, round, square and triangular.

The tool post is operated by lead screws that can accurately position the tool in a variety of planes. The tool post may be driven manually or automatically to produce the roughing and finishing cuts required to turn the work piece to the desired shape and dimensions, or for cutting threads, worm gears, etc. Cutting fluid may also be pumped to the cutting site to provide cooling, lubrication and clearing of swarf from the work piece. Some lathes may be operated under control of a computer for mass production of parts (see "Computer Numerical Control").

Metalworking lathes are commonly provided with a variable ratio gear train to drive the main lead screw. This enables different pitches of threads to be cut. Some older gear trains are changed manually by using interchangeable gears with various numbers of teeth, while more modern or elaborate lathes have a quick change box to provide commonly used ratios by the operation of a lever.

The threads that can be cut are, in some ways, determined by the pitch of the lead screw: A lathe with a metric lead screw will readily cut metric threads (including BA), while one with an imperial lead screw will readily cut imperial unit based threads such as BSW or UTS (UNF,UNC).

The work piece may be supported between a pair of points called centres, or it may be bolted to a faceplate or held in a chuck. A chuck has movable jaws that can grip the work piece securely.

There are some effects on material properties when using a metal working lathe. There is little chemical or physical effects, but there are many mechanical effects which include, residual stress, microcracks, work hardening and tempering in hardened materials.

1. Match the left part with the right:

2. Complete the sentences with the suggested words: screws; clearing; roughing; desired; also; cuts

The tool post is operated by lead______ that can accurately position the tool in a variety of planes. The tool post may be driven manually or automatically to produce the______ and finishing_______ required to turn the work piece to the_______ shape and dimensions, or for cutting threads, worm gears, etc. Cutting fluid may_______ be pumped to the cutting site to provide cooling, lubrication and_______ of swarf from the work piece.