Boring is one of the most common and important operations performed in machining. It is used to obtain holes of a precise diameter and high surface finish, as well as to produce cylindrical and conical surfaces. Borers are machine tools used for this kind of operation, which consists in enlarging the inner diameter of an already existing hole. The process is done either manually or automatically, depending on the required volume and quality of the result. Boring operations can be classified according to the type of cutter used. The three most common are known as reaming, single-point boring and multiple-point boring.
Reaming is used to finish and enlarge a hole. This operation is typically used to maintain or control the dimensions of a previously drilled hole, as the result is more accurate and the hole can be made cylindrical. A reamer consists of multiple cutting blades arranged around the circumference of its body. Single-point boring is performed by cutting the surface of the hole with the help of a single cutting tool that moves along the diameter of the hole. This process is used to modify the diameter of a hole and to produce conical surfaces. A simple boring bar, with a single point cutter secured at one end, is usually used. Finally, multiple-point boring is used to machining harder materials where a single-point tool cannot reach. A cutter composed of several cutting edges arranged around its circumference is used, and it can move both along and across the axis of the hole.
The most important factors to be considered when machining with a borer are the selection of the appropriate type of tool, the cutter geometry, the cutting speed, the feed rate, and the depth of the operation. The type of tool and the cutting speed should be selected according to the material of the workpiece, the size of the hole, and the roughness and hardness of the surface. The geometry of the tool will determine the quality of the cut, and the feed rate should be as fast as possible but without causing vibrations. Lastly, the desired depth of the hole should also be taken into account.
For machining harder materials, such as titanium or certain stainless steel alloys, extra measures might be necessary. This includes increasing the width of the cutting edge by using a double-sided cutting tool and the use of coolants or lubricants to reduce the tools’ wear. Boring operations are also employed to obtain inner and outer tapers. For example, inner tapers are used to form projections in plastic injection molding dies and stamping dies, while outer tapers are used to increase the size of a hole gradually. Borers are essential machine tools when it comes to obtaining precise holes in different materials, as they can provide accurate results at high productivity levels. The choice of the appropriate boring operation will depend on the features of the workpiece and the desired dimensions.
