Ex.17. Read the text B without a dictionary for 8 minutes and compare the similarity and difference of these operations.

 

LATHE RELATED OPERATIONS:

There are so many operations which a lathe machine can perform, but the most common are given below: • Boring • Drilling • Facing • Filing & Polishing • Knurling • Milling •Parting • Taper turning • Threading • Turning

TURNING: Reduction in the diameter of the work piece is called turning. There are four different types such as straight turning, taper turning, profiling or external grooving. Those types of turning processes can produce various shapes of materials such as straight, conical, curved, or grooved work piece. Turning uses simple single-point cutting tools

FACING: Reduction in length of the work piece is called facing operation. A lathe can be used to create a smooth, flat, face very accurately perpendicular to the axis of a cylindrical part.

BORING: Enlargement of the diameter of the holes is called boring operation. When boring is done in a lathe, the work usually is held in a chuck or on a face plate. Holes may be bored straight, tapered, tool parallel to the rotation axis of the work piece or to irregular contours.

PARTING: A parting tool is deeper and narrower than a turning tool. It is designed for making narrow grooves and for cutting off parts. When a parting tool is installed, ensure that it hangs over the tool holder enough that the holder will clear the work piece (but no more than that). Ensure that the parting tool is perpendicular to the axis of rotation and that the tip is the same height as the centre of the part. A good way to do this is to hold the tool against the face of the part.

THREADING: Threading can be performed on the lathe machine very efficiently because lathe machine is versatile operation machine. Two basic requirements for thread cutting are an accurately shaped and properly mounted tool is needed because thread cutting is a form-cutting operation. The second by requirement is that the tool must move longitudinally in a specific relationship to the rotation of the work piece, because this determines the lead of the thread. This requirement is met through the use of the lead screw and the split unit, which provide positive motion of the carriage relative to the rotation of the spindle.

TAPER TURNING: When the diameter of a piece changes uniformly from one end to the other, the piece is said to be tapered. Taper turning as a machining operation is the gradual reduction in diameter from one part of a cylindrical work piece to another part. Tapers can be either external or internal. If a work piece is tapered on the outside, it has an external taper; if it is tapered on the inside, it has an internal taper. There are three basic methods of turning tapers with a lathe. Depending on the degree, length, location of the taper (internal or external), and the number of pieces to be done, the operator will use the compound rest, offset the tail stock, or use the taper attachment.

Notes:

Knurling - насічка, накатка

Grooving – нарізка канавки

Filling – набивка, прокладка

Polishing – полірування

Offset – паросток, відгалуження

Attachment – пристрій, приладдя

 

Ex.18. Agree or disagree with the following statements.

1. Reduction in the diameter of the work piece is called facing.

2. Enlargement of the diameter of the holes is called boring operation.

3. A parting tool is designed for making wide grooves.

4. Thread cutting is a form – cutting operation.

5. Taper turning is the gradual enlargement in diameter from one part of a cylindrical work piece to another part.

6. Tapers can be either external or internal.

Ex.19. Answer the questions:

1. What the main machining operations do you know?

2. What cutting tools does turning use?

3. Where is the work held when boring is done in a lathe?

4. What is it necessary to remember when a parting tool is installed?

5. What basic requirements for thread cutting is needed?

6. Why must the tool move longitudinally in a specific relationship to the rotation of the work pies?

7. When is the piece said to be tapered?

8. What basic methods of turning tapers are there?

VII Oral practice

Ex.20. Speak on the main machining operations using the table:

 

 

Ex.21. Make up the dialogues on the situations.

1. You take the industrial practice at the plant. A foreman asks you about the main machining operations, their applications and advantages.

2. You are taking exam. Your question is “Basic engineering operations”. But you are in difficulties about it. The teacher is asking you some questions on the subject.

3. You could not visit the lecture “Basic machining operations” on account of your disease. But you want to know about the difference and the similarity of these operations. Ask your group – mate about it.

 

VIII. Reading and comprehension.

Ex. 22. Read the text C without a dictionary for 5 minutes and say what problems are mentioned in the text.

Text C

TYPES OF LATHES

All the machine-tools operate on either a reciprocating or rotary type principle; either the tool or work reciprocates or rotates. Cutting tools must be hard. A tool must also have the correct cutting angle, and the correct speed to cut satisfactorily. Heat dissipation is another factor in considering the correct speed. The engine lathe has a large range of spindle revolutions and of feeds, and in can cut threads. The bench lathe is adapted to small work, having a maximum swing capacity of 9 inches.

The shaper is a flexible machine in many respects complementing the lathe in the work it performs. It has a reciprocating cutting tool, which takes a straight-line cut. It can produce flat surfaces, and by means of special tools, attachments, and devices for holding the work, a shaper can also cut external and internal key-ways, spiral grooves, gear racks, dovetails, T slots and other shapes. The planer, a much larger and heavier machine than the shaper, is designed to remove metal by moving the work in a straight line against a stationary single-edged cutting tool.

The automatic lathe is designed so that all of the tool movements are automatically controlled, although the work must be inserted and removed by an operator. In the automatic lathe two or more heavy duty slides, each with its own drive, rate of feed and direction of feed may be applied. All functions of the machine are completely automatic, including advance of the platen to working position, feeding of all tools, and retraction of slides and platen at completion of cycle, at which time stopping of the spindle is also accomplished automatically. One operator may run two or more lathes. Such lathes are not limited to automative parts but are reducing production time and cost on pump parts, motor and generator parts, pipe flanges, brass and bronze castings, chuck bodies, bevel gears, airplane engine cylinders, etc.

Notes:

Shaper – поперечно – стругальний верстат

Planer – подовж – стругальний верстат

Dovetail – лапа, шип

Platen – станина

 

Ex. 23. Agree or disagree with the following statements:

1. All the machine – tools on neither a reciprocating nor rotary type principle.

2. A tool must have the correct cutting angle and the correct speed to cut satisfactorily.

3. The bench lathe has a large range of spindle revolutions and of feeds.

4. The shaper is a flexible machine in many respects complementing the lathe in the work.

5. The planer is designed to remove metal by moving the work in a parallel line against a stationary single – edged cutting tool.

6. The automatic lathes is designed so that all of the tool movements are automatically controlled.

Ex.24. Answer the following questions:

1. How do all the machine – tools operate?

2. What kind of work is bench lathe adapted to?

3. How can the shaper produce flat surfaces?

4. What is the structure of the automatic lathe?

5. What functions do the automatic lathe perform?

 

IX. Oral practice.