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close this bookCylindrical Turning and Face Turning - Course: Techniques for machining of material. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 19 p.)
View the document(introduction...)
View the document1. Objectives and purpose of cylindrical turning and facing
View the document2. Design and types of turning tools
View the document3. Preparation of cylindrical turning and facing
View the document4. Main movements for cylindrical turning and facing
View the document5. Cylindrical turning and facing of simple cylindrical parts
View the document6. Cylindrical turning and facing of shouldered cylindrical parts
View the document7. Cylindrical turning and facing of long cylindrical parts
View the document8. Cylindrical turning and facing of hollow cylindrical parts

7. Cylindrical turning and facing of long cylindrical parts

Long cylindrical parts can be machined with the part held in a chuck, between centres, but also sometimes using collets. The use of counter-supports is always necessary.

The cutting is done on the circumferential surface or end face of the part.

- You should always select the safest way of chucking/clamping for the relevant part The more chucking/clamping face you have, the more safe is the machining process.

- The tailstock with live centre and the stationary or follow steady rest are used as counter-support. Longer parts necessitate the combined use of tailstock and steady rest or of several steady rests.

- The use of the steady rest prevents deflection of long shafts and the production of chatter marks as well.

- For parts mounted overhung, the steady rest (without using the tailstock as counter-support) permits facing and boring operations to be performed, if it is used to support and guide the freely rotating end of the part (see Fig. 12).

- The contact faces of the steady jaws must be round and even. Sufficient lubrication during the machining process is necessary.

- For non-round or uneven contact faces the use of a scroll chuck (Fig. 24) is recommended.

- Areas of the part succeptible to deflection should be sup-ported by stationary steady rests mounted on the lathe bed. The length to be turned is then subdivided.

Figure 24 Scroll chuck

1 tailstock jaws,
2 scroll chuck,
3 tailstock,
4 work gripping in driver,
5 bearing surface

- Follow rests are mounted on the tool slide and perform the same feed movement as the turning tool. In this connection attention is to be paid to the facts that

· the steady rest top jaws must always be softer than the material of the part to be machined,

· the steady rest must be precisely aligned,

· the pressure of the top jaws on the surface of the part must not be too high (heat expansion),

· the top jaw contact faces must suit the diameter of the part,

- If any part shows heavy deflection, it must be straightened before machining.

- When machining long parts, the turning tool should be mounted slightly above centre to avoid hooking.

- The cylindricity is to be checked and, if necessary, corrected.

- A negative rake angle (tool face and side relief of the cutting tool) is useful for machining parts with a high length-diameter ratio.

What is the basic difference in the use of a stationary and follow rest?

What basic rules are to be observed when using a steady rest?