3. Preparation of cylindrical turning and facing

Before starting with cylindrical turning and facing, all tools and auxiliary means necessary for the work are to be duly and properly placed at disposal observing the following rules:

- Check the tools for serviceability.
Use serviceable tools only.
- Tools to be used must not be placed one above another.
- Store tools in clean condition.
- Store measuring and testing tools on adequate supports only.
- Select the necessary auxiliary means according to the work order and place them at disposal on adequate supports.

Setting up of the lathe (turning machine) basically involves the following steps:

Clamping/chucking of the parts

- Use three-jaw chucks for chucking of short rotationally symmetrical parts.

- Use stepped chuck jaws which can be turned out for premachined parts. Such jaws ensure safe chucking. The surface of the part will not be damaged.

- Use length blocks to suit the relevant lengths of the parts to be machined. The length blocks are to be placed one after another, between the end stop and longitudinal slide, corresponding with the length of the part to be machined.

Figure 10 Length block

1 machining and length-block length

- For long parts use the follow or stationary steady rest.

Figure 11 Follow rest

1 pressure jaws
2 application of coolant/lubricant

Figure 12 Use of the stationary steady rest

- For parts to be machined in one setting use the driving centre.

Figure 13 Driving centre

Clamping of the tools

When clamping the turning tool make sure it is in centre position.

Setting of the cutting values

The values to be set depend on the kind of turning operation and on the setting possibilities of the lathe. The cutting speed (V) depends on the material of the tool and is given in the list below:

WS (tool steel)	- V = 6 - 25 m/min
SS (high-speed steel)	- V = 25 - 50 m/min
HSS (super high-speed steel)	- V = 50 - 80 m/min
HS (carbide)	- V = 80 - 120 m/min.

What rotational speed (n) will be necessary for machining a part of 50 mm diameter using a carbide tipped tool?

(V, the cutting speed, is to be determined on your knowledge or to be taken from the above list)

1. for the cylindrical turning technique
2. for the facing technique.

Formula:

given:

required:

Calculation for cylindrical turning

n = ______________ (r.p.m.)

n = ______________

Calculation for facing

n = ______________ (r.p.m.) Attention d/2 !

n = ______________

- Provide lubricant and coolant to prolong the tool life and ensure proper chip removal.

- Let the tool take the first cut on the circumferential surface or end face of the rotating part.

- Return the tool slide to initial position.

- Feed setting, graduated dial to be set to "0". If in setting to final size, by the crank-handle of the tool slide, the respective scale value was exceeded by mistake, turn the crank--handle in the opposite direction by approximately one revolution (because of the lost motion of the spindle) and re-set.

- Switch on the feed motion - do not forget length setting. The power feed is selected according to the desired surface roughness (Rz) and chip pattern (short-chipping).

- Switch off the feed motion.

- Return the tool slide to initial position. When the final size is achieved, avoid damage to the surface by lifting the turning tool clear off the surface machined.

- Dimensional and visual inspection

What is the purpose of chucking in stepped chuck jaws which can be turned out?
______________________________________________
______________________________________________
______________________________________________

What is to be done if in setting to final size by the crank-handle of the tool slide the respective scale value was exceeded by mistake?
______________________________________________
______________________________________________