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Text A. Types of Machine Tools

Section I. Reading material.

I. Read the text and translate it into Russian in written form.

Text A. Types of Machine Tools

We couldn't begin to describe all machine tools in detail here. There are too many. There are shapers, lathes, drill presses, grinders, planers, and others. Some machine tools turn out metal parts that become parts of other machines. Some turn out products that you buy in stores. Machines range from simple bench gadgets to huge masses of metal that weight tons and perform complicated tasks, called numerically controlled (NC) machines. We'll discuss only machine tools-power-driven machines that shape metal by removing chips. The following are the basic types:

Milling machines are used to cut away and shape metal by means of sharp-edged cutting wheels that are forced against the work. The wheel rims have many cutting edges.

Planning machines smooth the surface of metal as a carpenter's plane smoothes a board. But the cutting tool is fixed and the metal you are planning moves back and forth. A shaper belongs in this group. However, the cutting tool of a shaper moves forth and back and the metal is clamped down.

Boring machines cut around hole. The work is usually clamped on a plate, and a revolving drill bore, or reamer is brought down against it.

Grinding machines smooth and shape metal by the use of rotating grinding wheels. These grinders cut away the metal or they may merely smooth it, depending on the job.

Turning machines, such as lathes, shape metal by revolving the metal against a fixed cutting tool. The result is a cylinder-shaped surface.

The main parts of lathes are: the headstock, which usually contains the gearing mechanism; the chuck, into which the job is clamped; the tailstock, which can be moved along the bed to adjust the distance between the chuck and the tailstock centre; and the carriage consisting of the saddle and the cross slide on which the toolholder with the tool is mounted. The speed at which the lathe turns can be adjusted either by regulating the speed of the motor driving it, or by the gearing. The automatic turret lathe is a perfection of the ordinary lathe. Its tools are changed automatically. A worker skilled in the use of a lathe is called a turner.

Numerically controlled (or NC) machines are capable of doing several jobs at the same time. The machine is programmed usually by punched or magnetic tape to perform specific tasks. A different job can be completed by the machine by changing its program, or tape. The use of NC is most dramatically seen in the aircraft aerospace industry, where it shapes metals into complex curves and contours by controlling the characteristics of chemicals, electricity, magnetism, liquids, and the like to create sophisticated parts. More down to earth, it can produce several identical parts of identical quality at the same time, switching from inch to metric.

The introduction of NC machines has been a boon to metalworking industries and has created several new types of jobs, discussed later.



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