MACHINE-TOOLS

Before metal is formed into the required shape, it has to undergo a number of processes, such as casting, rolling, forging, welding, piercing, trimming, spinning, bending, drawing, etc. The machines which work on the surface of the metal piece, or provide it with grooves or holes or with a thread are called machine-tools.

The term machine tool is usually reserved for tools that used a power source other than human movement. The first machine tools offered for sale were constructed by Matthew Murray in England around 1800.

The most common machine-tool found in almost any workshop is the lathe, in which the job spins round its axis while a cutting tool is working on it. Its main parts are: the headstock, the chuck, the tailstock, the lathe bed, the carriage. The headstock usually contains the gearing mechanism. The job is clamped into the chuck. The tailstock can be moved along the bed to adjust the distance between the chuck and the tailstock centre. The carriage consists of the saddle and the cross slide on which the tool holder 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.

Other machine-tools work on plane surfaces for example milling machines, and also planning and shaping machines. A broaching machine employs broaches to make non-circular holes. Circular holes are drilled by a drilling machine or bored by a boring machine or a boring mill. Gear cutting machines include gear milling machines, gear shapers and gear grinding machines. Thread milling machines are used in the production of threads on shafts and on other machine elements.

All these machines use cutting tools, usually made of high-speed steel; grinding machines, on the other hand use abrasives such as diamonds, diamond dust, corundum, silicon carbide, etc. Honing and lapping machines also use abrasives; they enable us to obtain a smooth finish of less than 001 mm.

Задание 2:

ответьте на во к тексту:

1.What machines are called machine tools?

2.When was constructed the first machine tool?

3.What is the most common machine tool?

4.What are the main parts of the lathe?

5.What other machine tools do you know?

6.What machine tools are used for making circular holes?