Tooling

The tools used in turning centres are different from that of the machining centres. Generally, the single point tools are used for most applications, while the multipoint tools such as drills are used occasionally. More multipoint tools are used in machine tools with more than two axes control such as those used in turn mill centres. In this unit, we will concentrate on the conventional machines with two-axis control. Hence, most of the exercises we should be dealing will have single point tools. However, there are a large variety of tools available and their choice will have to be done carefully.

The various operations that will be commonly done in turning centres using single point tools are:

Facing

This involves generating a plane surface perpendicular to the axis of revolution generally at the end of the workpiece. In this operation, the tool will be fed perpendicular to the axis and therefore should have an approach angle that the body of the toll will not touch the work piece.

Turning

This is the most common operation that generates a cylindrical surface on the outside of the work piece. The other possible variations could be tapered cylindrical surfaces or some contoured surfaces. Bulk of the operations done will fall in this category. The operations are generally classified into rough turning and finish turning. In the case of rough turning operation most of the material will be removed in straight cuts with large depth of cut and lower cutting speed. The finish cut removes very small amount of material (typically 0.5 to 1.0 mm) with very high cutting speed and small feed rate to achieve the requisite finish. The tools, therefore, will have to be selected based on the requirement. The rough turning tools generally will be used to generate rectangular cuts with large depth of cut with a large included angle for the tool bit (for strength). The finish turning tool is generally used to generate the finish profile and will generally use the insert with a small included angle. The tool manufacturer's catalogue should give the necessary selection procedures for the individual application based on the part geometry being generated.

Grooving

Used to make small grooves either internal or external using grooving tools. The feed (in X-axis) is directly given perpendicular to the axis of revolution.

Parting

Used to cut off the part from the raw material that is generally a long bar. This is similar to grooving. The tool is fed perpendicular to the axis of revolution beyond the centreline of the stock.

Boring

It is similar to the external turning operation, except that it is done for internal operations such as hole enlargements.

Threading

It is used for making the threads either on external or internal surface.