Read and translate the text.

Machinability

Machinability is a very complex mechanical property, and it has been impossible to measure it by any of the simpler mechanical tests. For example, ordinary steels having a Brinell number of not over 200 are readily machinable, while manganese steel of a Brinell well under 200 is not machinable. For cutting gear teeth in forged steel, the steel is heat-treated to a Brinell hardness of about 160 to 170. If the Brinell hardness is 150 or less, the material will be too tough and plastic to machine well. Copper and aluminum, because of their softness and toughness, are not easily machined.

Metals may be so strong that it is difficult to produce a tool capable of lifting the chip without frequent failures. Again, metals may contain hard constituents which quickly dull the point of the tool. Some metals are so strong and tenacious that, at what is considered as reasonable machining speed, the temperature developed soon limits the tool life. This is one of the most common causes of failure in commercial work. Gray cast-iron machines readily because the flaky graphite particles in it cause the chip to break readily. Malleable cast iron also machines easily, but the nodular shape of the free carbon is not so effective in breaking the chip. Wrought iron, which carries many tiny threads of slag, machines easily until the harder slag dulls the tool.

In spite of the difficulty of measuring machinability, it has been defined as the ease with which a material can be machined. The most machinable metal may be said to be one that permits the fastest removal of the greatest amount of material with a satisfactory finish before resharpening of the tool is required. Several methods have been used to evaluate machinability, such as the power consumed under some standard condition, the rate of tool penetration under some standard condition, the temperature produced under specified conditions, and so forth.

Text C

New words and word combinations:

1) turner – токарь; 2) ways-guide – направляющие станка; 3) carriage – суппорт, каретка; 4) cross-slide – поперечные салазки, поперечный суппорт; 5) clamp – зажимать, зажим; 6) bed – станина; 7) headstock – передняя бабка; 8) tailstock – задняя бабка; 9) feed mechanism – механизм подачи;  10) mount – устанавливать, монтировать; 11) casting – отливка; 12) align – выпрямлять, центрировать; 13) sleeve – втулка, рукав; 14) traverse – двигаться, передвигаться; 15) angle – угол; 16) saddle – салазки, суппорт;      17) apron – фартук токарного станка; 18) taper bore – коническое отверстие; 19) live centre – вращающийся центр, передний центр; 20) dead centre – неподвижный центр; 21) chuck – патрон (зажимной); 22) rectangular – прямоугольный; 23) facilitate – облегчать; 24) graduate – градуировать.

Read and translate the text.

Engine lathes

Modern lathes are highly efficient, accurate and complex devices, capable of doing a great quantity and variety of work. A well constructed engine lathe will, when properly operated, produce work accurate within 001 of an inch or even less. Motion is transmitted to modem lathes by means of individual motors. Sometimes the motor is direct mounted, while on other machines it is connected by means of a short belt, usually of the V-type. The size or capacity of a lathe is given in terms of swing and length of bed.

The swing refers to the diameter of work that can be rotated in the lathe. Thus a 16-inch lathe will swing work as large as 16 inches in diameter. The length of a lathe should not be confused with the maximum distance between center when the tailstock is moved to the rear end of the lame bed. The maximum distance between centers, however, determines the length of stock that can be machined.

Lathes are made in a wide variety of types and sizes, from the small precision lathe found in watch repair shops to the immense machine used in manufacturing big guns. In recent years manufacturers have produced attachments which can be employed on a lathe to perform functions or operations formerly done on a special machine: a milling attachment, a boring attachment and a gear-cutting attachment. Such devices greatly extend the variety of work that can be performed on a lathe.

The most versatile machines of the lathe group are engine lathes. They are for metal-cutting operations and for cutting threads. Because of their ability to perform various kinds of work they require a great degree of skill to operate.      A worker skilled in the use of a lathe is called a turner. Engine lathes vary in size. The size of the engine lathe is based upon two measurements – approximate largest diameter that can be revolved over the ways and the total bed. The engine lathe is fitted with a carriage and cross-slide for damping and holding the cutting tool. In engine lathe the cutting tools are generally guided by the machine tools itself, in other words, they are operated mechanically, while in some lathes the cutting tools are guided by hand. The engine lathe consists essentially of the following basic parts: the bed, the headstock, the tailstock the feed mechanism, and the carriage. All the principal units are mounted on a bed. The bed has the ways or guides along which the carriage and the tailstock travel. The bed is a strong casting, which function as a base for supporting and aligning the rest of the machine. The work is clamped and rotated by the headstock. The headstock is located and firmly bolted to the left-hand side of the bed and carries a pair of bearings in which the spindle rotates.

Many modern lathes have a motor built into the headstock with the spindle serving as the motor shaft. The tailstock is located at the right-hand side of the bed. It is a casting carrying a non-rotating sleeve, which can be advanced or retracted by means of the revolving screw. The tailstock may be moved anywhere along the lathe bed and can be clamped in place at any point. The cutting tool is traversed in both the longitudinal and cross directions, as well as at an angle, by means of the carriage. The carriage consisting of the saddle and apron is the movable part which slides between the headstock and tailstock.

Text D

New words and word combination:

1) to be responsible for – быть ответственным за; 2) to occur – случаться, иметь место; 3) activity – деятельность; 4) typing – печатание (на машинке); 5) wheel – колесо; 6) axle – ось, мост; 7) hardware – аппаратура; аппаратные средства; 8) gear – зубчатая передача, шестеренка; 9) to provide – обеспечивать; предусматривать; 10) to supply – снабжать, поставлять;      11) source – источник; 12) inanimate – неживой, неодушевленный; 13) to supervise – смотреть, наблюдать за; 14) to modify – видоизменять; 15) to set the machine – наладить машину; 16) camshaft – кулачковый, распределительный вал; 17) to fit – устанавливать, подгонять, прилаживать; 18) assembly line – линия сборки.