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Chapter 3. How to Use a Lathe

Basic Operation of a Lathe

Let's Use a Lathe!

A lathe is a machine tool which turns cylindrical material, touches a cutting tool to it, and cuts the material. The lathe is one of the machine tools most well used by machining (Figure 1).

As shown in Figure 2, a material is firmly fixed to the chuck of a lathe. The lathe is switched on and the chuck is rotated. And since the table which fixed the byte can be moved in the vertical direction, and the right-and-left direction by operating some handles shown in Fig. 3. It touches a byte's tip into the material by the operation, and make a mechanical part.

Fig.1, Appearance of a Lathe

Fig.2, Chucking of Material

Fig.3, Handles of a Lathe

@When we use a lathe, the following things must take great care.
(1) Don't keep a chuck handle attached by the chuck. Next, it flies at the moment of turning a lathe.
(2) Don't touch the byte table into the rotating chuck. Not only a byte but the table or the lathe are damaged.

Three Important Elements

In orger to get an efficient propcess and beautiful surface at the lathe machining, it is important to adjust a rotating speed, a cutting depth and a sending speed. Please note that the important elements can not decide easily, because these suitable values are quiet different by materials, size and shapes of the part.

Rotating Speed
It expresses with the number of rotations (rpm) of the chuck of a lathe. When the rotating speed is high, processing speed becomes quick, and a processing surface is finely finished. However, since a little operation mistakes may lead to the serious accident, it is better to set low rotating speed at the first stage.

Cutting Depth
The cutting depth of the tool affects to the processing speed and the roughness of surface. When the cutting depth is big, the processing speed becomes quick, but the surface temperature becomes high, and it has rough surface. Moreover, a life of byte also becomes short. If you do not know a suitable cutting depth, it is better to set to small value.

Sending Speed (Feed)
The sending speed of the tool also affects to the processing speed and the roughness of surface. When the sending speed is high, the processing speed becomes quick. When the sending speed is low, the surface is finished beautiful. There are 'manual sending' which turns and operates a handle, and 'automatic sending' which advances a byte automatically. A beginner must use the manual sending. Because serious accidents may be caused, such as touching the rotating chuck around the byte in automatic sending,.

Fig.4, Three Important Elements

A beginner of a lathe must operate with low rotating sopeed, small cutting depth and low sending speed.

Cutting Tools for Lathe

There are vrious kinds of the cutting tools for a lathe. We must choose them by the materials and shape of a part. Three typical cutting tools are introduced in follows. Then we consider what is an easy process or a hard process.

Form of Typical Cutting Tools

Figure 5(a) shows the most well-used cutting tool called a side tool. It can process to cut an outside surface and an edge surface. Since the material is set at the right of lathe, then this tool can only cut the right of the material.

The cutting tool shown in Figure 5(b) is used at parting and grooving processes. Its pointed end is slim, then it is too weak. Don't add a strong side-force to the tool. This tool must send vertical direction only.

The cutting tool shown in Figure 5(c) is called a boring bar. It is used to cut at an inside surface. It can make a big hole, which cannot be process by a drill, and an high accurate hole.

Fig.5, Typical Cutting Tools

Easy Processing and Hard Processing

The general cutting tool, shown in Figure 5(a) is the most easy hangling. Then the shape, which can be make using only the general cutting tool, has easy processing.

In the case of the parting or prooving, The process becomes hard with decreasing of the width of a alot, and increasing of the depth.

In the case of using of the boring bar, the process of a penetrated hole is not so hard. But the process of no-penetrated hole is somewhat hard. Because we cannot see the bottom surface in during process. In such cases, we decide the location of the tool with the sound or the scale of lathe. Moreover, the process of a small hole (less than 10 mm) or a depth hole is too hard.

Of course, there are impossible shapes as shown in Figure 6(c). In such case, the part must be divided or have any contrivances.

Fig.6, Easy Processing and Hard Processing

Hearing the Sound

In the case of the lathe process, sharpness is known from scraps of the material or a processing surface. In addition, it is also important to hear the sound. For example, when the sound is too high, the processing is not suitable. It is caused by the bad edge of the tool, too higher rotating speed of the lathe, or vibrating of a thin material.

Setting of a Cutting Tool

In case a cutting tool is fixed to a table, thin metal plates are put between the tool and the table, and the height of the edge is adjusted to the center of material.

In the case of using the general cutting tool, when the edge is higher than the center of material, the edge of a blade does not hit the material, and it cannot cut at all. Conversely, if the edge is low, it becomes impossible to cut the center of material. Moreover, the scale of a handle does not have correct value, then accurate processing becomes impossible.

Fig.7, Height of Edge

If it says which it is ...

Though the height of the cutting tool is adjusted in careful, we cannot unite with the center of material completely. Therefore, we have to set the tool to the direction, that the edge is easy to touch the material. The general cutting tool and the parting tool have to be set a few low position. The boring bar has to set a few high position.

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