IV. Comprehension.

Ex.12. Agree or disagree with the following statements:

1. A lathe is known to be a machine - tool for producing and finishing surfaces of workpieces.

2. The machine tool may be subjected to the action of a cutting tool moving in a vertical plane through the axis of the work.

3. When the cutting tool moves in a longitudinal direction to the axes the operation is known as “milling”.

4. When the cutting tool moves in a parallel direction it is known as “facing”

5. Lathers are known to be of different designs and sizes

6. Lathes in which workpieces to be treated are held in a chuck as known as turret lathes.

7. Bench lathers are intended for small work of considerable accuracy.

Ex.13.Answer the questions:

1. What is the most versatile machine tool in the mechanical engineering industry?

2. What the main operations is lathe designed for?

3. What are the main types of lathe?

4. What does the engine lathe consist of?

5. Where can you find a headstock and a tailstock?

6. Why is the spindle the most important part of a lathe?

7. What does the feed mechanism comprise?

8. What is the carriage used for?

Ex.14.Fill in the tables

A )

Application

B

Application

)

V. Oral practice.

Ex.15. Speak on the topic “Lathes” using the tables of ex.13.

Ex.16. Prove that the lathes are the most important and useful machine – tools for mechanical – engineering.

VI. Reading and comprehension.

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?