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7. Drills and drilling

Drilling is one of the cutting operations producing cylindrical holes of different diameter in solid material by means of rotating tools called "drills" (Fig. 22).

The most common type of drill in use1 is the twist drill made of a tempered steel round bar stock. Twist drills are made with two, three, or four spiral grooves or flutes milled from the solid. These grooves or flutes winding around the body of The drill serve for forming the cutting edges of the drill, as well as for removing the chips formed in drilling from the hole.

Straight-Shank Drill

Tapered-Shank Drill

Fig. 22. Drills.

The twist drill comprises three principal parts: body, shank and point. The twist drill has two cutting edges known as the "lips". These cutting edges, or lips, are connected e by a third edge, called a "web". It is this part that gives rigidity and strength to the drill. When in use the first two cutting edges remove the material

from the work, while the third one penetrates into the material by rubbing rather than cutting.

In order to drill holes in a metal the cutting edges of a drill should be correctly ground to a certain angle. When a drill is ground correctly, its cutting edges, or lips, should have equal length whereupon each of them should make the same angle with the centre line. Otherwise the drill will make holes the diameter of which is larger than that of the drill. This may disable the drill and cause an undesirable waste of material. Drills have shanks of various types, the most commonly used being those having straight and tapered shanks. The shank of the drill serves for clamping the drill either in the chuck spindle or socket of a drilling machine. The above part of the drill may be either of a cylindrical shape, like in2 straight-shank drills, or of tapered shape in tapered-shank drills.

The third part of the drill is called a "drill point". It is always ground to a cutting angle varying with the kind of material to be drilled. For hard materials this cutting angle equals 140° and for soft materials it equals 90°. The cutting edges of flat drills used for drilling holes in steel or in cast iron are ground to an angle of 100° to 120°. All the drills get worn while drilling and they should be re-ground from time to time.

1. The most common type of drill in use -самым обычным используемым типом сверла...

2. like in - как в, подобно

Exercises

I. Use the following words and phrases in sentences of your own:

to drill, cylindrical holes, rotating tool, twist drill, flute, to mill, lips, web, spiral grooves, tapered shank, socket

II. Retell the text giving answers to the following questions:

1. What is drilling, and its purpose? 2. By means of what tools is drilling performed? 3. Which is the most widely used tool for drilling? 4. What material is a twist drill made of? 5. What purposes do twist drill flutes serve? 6. What are the principal parts of a twist drill? 7. What are the cutting edges of a twist drill called? 8. What part of the twist drill gives it rigidity and strength? 9. Why should the cutting edges of a drill be correctly ground'? 10. Why should the cutting edges of a drill have an equal length?

III. Form adverbs from the following adjectives:

proper, cylindrical, certain, good, wide, correct, equal

IV. Underline the suffixes and prefixes and translate into Russian the following groups of words of the same stem:

to desire, desirable, undesirable; cylinder, cylindrical, cylindrically; to straighten, straight; to grind, ground, re ground; equal, equality, equalization, to equalize, equalizer, unequal, unequalled

V. Supply the missing words:

1. In drilling h... in metal, heavy pressure must be applied at the drill p.... 2. Spiral f... are found on most drills. 3. The c... angle at the outer corner of the l... should be about 12. 4. The cutting edges of t... d... have angles of top rake and clearance the same as any other с… t... have. 5. The body of metal between the flutes forms what is called the w.... 6. The drills are held in place by their t... shanks or by gripping straight-s... drills in a c...

VI. Connect the following sentences using the con junction either... or:

Example: The body of the twist drill has two spiral grooves. The body of the twist drill has flutes cut on its surface.

The body of the twist drill has either two spiral grooves or flutes cut on its surface.

1. The twist drill is formed by twisting grooves in a fiat piece of steel. The twist drill is formed by milling a cylindrical piece of steel. 2. The grooves serve to form cutting edges of the drill. The grooves serve to remove the chips formed in the process of drilling. 4. The drill flutes serve to lubricate the drill. The drill flutes serve to remove chips from a hole being drilled. 5. The work to be drilled should be clamped in a vice. The work to be drilled should be clamped in a chuck. 6. The web of a drill penetrates into the material being cut. The web of a drill rubs the material.

VII. Translate the following sentences into English using the past participle instead of the attributive clauses:

Example: Часть сверла, которая называется режущей частью, всегда затачивается под определенным углом резания.

The part of the drill called a "drill point" is always ground to a certain cutting angle.

1. Операция, которая выполняется при помощи инструмента, называемого «сверлом», называется «сверлением». 2. Стружки, которые образуются при сверлении, удаляются по канавкам сверла. 3. Режущие кромки сверла, которые используются для сверления, должны затачиваться под определенным углом. 4. Инструмент, который используется для сверления, называется «сверлильным сверлом». 5. Одна из кромок сверла, которая называется «перемычкой», не режет металл.

VIII. Analyze and translate the following sentences:

1. Different kinds of drills are used in drilling, such as: a single-lipped twist drill, normally less than 1" (inch) in diameter. 2. It is formed of a tubular shank which is twisted of seamless tubing to make a single flute. 3. Coolant is carried through the hollow shank, through a small hole in the drill tip, and chips are washed out through the single flute. 4. A four-lipped hollow core drill is designed to carry chips out through a hollow drill shank. 5. This tool is used for enlarging holes and not for drilling solid metal. A two-lipped hollow type deep drill normally is used in drilling solid metal holes ranging from 1" to 3" in diameter and the tip is attached to a tubular steel shank. 7. Coolant carries chips through the flute into the centre of the drill and then out through the hollow shank. 8. Drills of the same design are also used for holes larger than 3". 9. These are provided with replaceable blades in the tip.

IX. Describe Fig. 22 orally using the following words and word combinations:

the body of a twist drill, to represent, a cylindrical rod, to have two spiral grooves, to serve, forming, the cutting edges of the drill, to be called lips, the lips, to be connected, a third edge, to be known., a web, to penetrate into material by rubbing, the shank, the drill, clamping the drill in the chuck, to be of different shapes, cylindrical shanks and tapered shanks, the third part of the drill, a drill point, to be ground to a cutting angle, to depend on, material to be drilled