How boring is done and what it is used for

Boring is a process carried out to enlarge a hole or improve its quality using mechanical tools. There are many tools available for boring holes. Each tool covers a specific range of diameters and may be designed for precision boring or for roughing.

What is boring used for?

Boring is directly related to existing holes that need to be enlarged in order to improve them. This function can be used for the following operations:

Step boring

This is the type in which the boring tool carries inserts of multiple diameters and axial heights.

Reaming

In this case, multi-edge tools are used, which are characterised by offering very high accuracy when producing holes. To achieve this, multi-edge tools must work to a tight tolerance and with a small radial depth of cut.

Multi-edge boring

Unlike reaming operations, here roughing operations are carried out that focus on the average amount of material removed. Thanks to this, a high feed per revolution is achieved when boring the hole.

Single-edge boring

These operations are usually carried out only when the power of the machine is limited. However, they can also be carried out when a finish or roughing is required if the material demands swarf control.

Factors to consider when boring

To bore correctly, several factors must be taken into account. The most important are a stable set-up, swarf control and the selection of a suitable insert.

A stable set-up for boring

When it comes to a stable set-up for boring, it is very important to concentrate on torque transmission and on the bending resistance of the tool holder to be selected. These characteristics are directly related to the quality and stability of the hole, so they must be adjusted to the type of hole to be machined.

In addition, here are some additional recommendations for achieving a stable set-up for boring:

• The adaptor should be as small as possible.
• The strength of the adaptor should be as high as possible.
• If the type of hole requires a reduction, it is recommended to use a tapered adaptor.
• When working with long overhangs, the best option is anti-vibration adaptors. It is also essential to have an adaptor that provides rigid clamping and, optionally, flange contact with the spindle.

Swarf control in boring

Besides a stable set-up, an optimal boring operation needs effective swarf control. Swarf evacuation and formation are especially important if you want to carry out blind-hole operations.

If swarf control is not given enough importance, problems such as swarf jamming can arise, which adversely affect the quality of the hole and the reliability of the process and can even reduce tool life.

To achieve optimal swarf control, the insert geometry must be selected carefully, and this must take the cutting data into account. The use of coolant is also recommended, as it not only helps to extend tool life but also makes swarf evacuation easier.

On the other hand, if the cutting data are not suitable, the cutting forces may be excessive or the swarf may even be too short or too thick. These problems can also cause vibration and deflection, which will adversely affect the accuracy of the operation.

It is worth mentioning that if large pieces of swarf become jammed in the hole, the insert may break and the surface finish will deteriorate. You can tell that the swarf is of optimal size when it looks like a comma or a spiral, so that it can leave easily through the hole.

In summary, to achieve optimal swarf control, the following factors must be taken into account:

• The material to be machined.
• The nose radius.
• The macrogeometry and microgeometry of the insert.
• The cutting speed, feed and depth.
• The lead angle or approach angle.

Choosing the right boring insert

Finally, to achieve perfect boring, the perfect insert must be selected. This aspect is related not only to the swarf control already mentioned but also to the quality of the work. To select a suitable insert, the nose radius, geometry, shape and size must be considered.

To select the right insert, you must first define the characteristics you want to prioritise. For example, if you want to prioritise insert strength and cost-effectiveness, the point angle should be as large as possible.

Conversely, if the priority is low vibration, the nose radius should be as small as possible.