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Mechanical engineering |Машиностроение

 Lesson 4

Read the text:  Drilling machines

The operation of drilling may be defined as "producing a hole in solid material by means of a rotating tool, having two cutting edges, that is forced or fed against that material". Other operations, such as boring, reaming, etc., all require an existing hole in the material before they can be performed.

The essential feature of a drilling machine is a rotating spindle pro­vided with a Morse taper socket, or, alternatively, a chuck, in which drills or tools can be fitted, and a feeding mechanism for feeding it towards the work. The spindle must run truly in rigid bearings, and must be provided with a thrust bearing to take the thrust of the cut.

CLASSIFICATION

Drilling machines are used mainly for drilling holes in machine parts, are made in many different types designed for handling the various classes of work to the best advantage, and the different types are also built in a great variety of sizes, because the most efficient results can be obtained with a machine that is neither too small, nor too large and unwidely for the work which it performs. Drilling machines of different designs are classified in various ways.

The upright drilling machine is the type most commonly used, and the name applied to this class indicates that the general design of the machine is vertical, and also that the drill spindle is in a vertical position.

The radial drilling machine. The main advantage of a radial machine is that the drill can be moved over the work to any desired position, so that a large number of holes can be drilled in the work without moving it. This type also has the advantage that large and heavy castings can be placed on the bed and drilled without locating them accurately.

The sensitive drill is another vertical or upright design, but it is classified as sensitive because it is a comparatively small machine of light construction, which possesses sensitive qualities which are of value in drilling holes in delicate work from 1/16  in. to ³/₄ in. diameter.

The multiple-spindle type is built in both vertical and horizontal design. It is essentially a production machine and is made in a variety of types. Sensitive drills for light accurate work are often fitted with a number of heads on one column, also there may be one head only.

A multiple-spindle machine can perform a number of operations on a component without the necessity of changing tools or removing the component from the jig. The function of this machine is to drill a number of holes in a piece of work at one time and to reproduce the same pattern of holes in any number of pieces accurately enough to make them inter­changeable. Its advantage lies in its flexibility.

Gang Drills. — When a number of single-spindle drilling machine columns are placed side by side oh a common base and have a common work table, the machine is known as a gang drill. Each spindle is independently controlled as to speed and feed so that a number of operations may be performed in succession and simultaneously upon the machine. In this machine work is moved progressively from one spindle to the next. Gang drills are excellent production machines. They are general-purpose in function but when equipped with the proper jigs and other auxiliary equipment they can serve as single-purpose machines for high production.

Fixed Multiple-Spindle Drilling Machines. — These machines are definitely single-purpose machines with the spindles fixed in the required pattern for a given purpose. They will produce that pattern accurately and indefinitely on many pieces. These machines may not only be vert­ical but horizontal or even angular. Each directional head has its own individual motor drive and feed and is, in effect, a self-contained unit. A vertical cylindrical column is mounted on a heavy cast-iron base and carries a radial arm. This arm is provided with horizontal ways along which slides the drilling head carrying the vertical drill spindle and power feed mechanism The spindle is counterbalanced or spring loaded to return it to its top position. This design enables a large' number of holes to be drilled fn heavy work without moving the work, as in large castings, and also enables holes to be drilled a long way from the edge of the work as in plate work. On some machines the work table is also mounted on the vert­ical column and can be raised or lowered or swung round the column.

The drive can be arranged by a constant speed motor mounted on an extension of the base, or on an extension of the radial arm or by a vertical constant speed motor or a variable speed motor  mounted on the drilling head itself.

 

1. Match the left part with the right:

 

 

2. Complete the sentences with the suggested words:  bed, move, hole, drill, casting, advantage

 

The main____ of a radial machine that the drill can be ___ over the work to any desired position, so that  a large  number of ___can be___ in a work without moving it. this type also has the ____that large and heavy ___can be placed on the bed and ____ without  locating them accurately.