Turning in its simplest meaning is the process of using a single point tool in order to achieve a cylindrical surface. Turning has a more specific operation which is generating an external cylindrical surface in which the orientation is parallel to the axis of the workpiece. When the orientation applied to generate a cylindrical surface is perpendicular to the workpiece rather than parallel, the process is called facing. In the process of turning, the direction in which the motion is fed is usually axial in relation to the machine spindle while in facial, it is fed radially. When both modes are required in cases of tapered and contoured surfaces, the process is referred to as profiling.
Most turning applications have the same characteristics. Only one cutting tool may be used for each surfaces and it must, to some extent, hang over the holder to make sure the space around the rotating workpiece is clear. During the cutting process, the workpiece and the turning tools used are in contact until it is done thereby making sure that the speed and the dimensions being cut away is constant around the cylindrical surface. While in the case of facing, the speed is proportional to the diameter of the workpiece meaning the speed decreases as the center of the workpiece is reached. In order to increase the speed of the rotation as it moves to the center, a spindle mechanism that changes speed may be utilized.
In order for turning to be successful, the conditions must remain constant while undergoing the metal cutting process. With an exception at the start and the end of the cut, the force of the cutting tool and the temperature of the tool tip must not vary. Facing is a special case where the temperature of the tool tip changes as the cutting speed changes. Despite the changes in speed, the force of the facing tool remains constant because of the small effect which is negligible.
Here are some of the most common operations which can also be performed aside from turning and facing:
- Chamfering. It is done by cutting an angle on a cylinder’s corner.
- Parting. When the end of a part needs to be cut off, the turning tools are positioned radially and fed into the workpiece at a certain location within its length.
- Boring. Done when a hole done previously needs to be enlarged. The tool must be linear and parallel to the axis of rotation.
- Threading. Used to produces threads, either internal or external. The tool must be fed outside or inside a surface in a linear position.
- Drilling. Used when a hole needs to be created in the workpiece. After the hole is created, reaming or boring must be performed in order to improve the accuracy and to make sure the surface is fully finished.
- Knurling. Done when cross-hatched pattern is needed on the surface of the workpiece.