Machining: An Introduction
Machining can be defined as the process of removing material from a work piece in the form of chips. The term, metal cutting is used when the material is metallic. Most machining has a very low set-up cost compared to forming, molding, and casting processes. However, machining is much more expensive for high volumes. Machining is necessary where tight tolerances on dimensions and finishes are required.

The machining section is divided into the following categories:

Drilling
Drilling is easily the most common machining process. Drilling involves the creation of holes that are right circular cylinders, typically by using a twist drill. The figure below illustrates a cross section of a hole being cut by a common twist drill.

The chips must exit through the flutes to the outside of the tool. As can be seen in the figure, the cutting front is embedded within the work piece, making cooling difficult. The cutting area can be flooded, coolant spray mist can be applied, or coolant can be delivered through the drill bit shaft.

Drilling Characteristics
The characteristics of drilling that set it apart from other powered metal cutting operations are:

The chips must exit out of the hole created by the cutting.

Chip exit can cause problems when chips are large and/or continuous.

For deep holes in large work pieces, coolant may need to be delivered through the drill shaft to the cutting front.

Of the powered metal cutting processes, drilling on a drill press is the most likely to be performed by someone who is not a machinist.

Drill Press Work Area
A view of the metal-cutting area of a drill press is shown below. The work piece is held in place by a C-clamp since cutting forces can be quite large. It is dangerous to hold a work piece by Hand during drilling since cutting forces can unpredictably get quite large and wrench the part away. Wood is often used underneath the Part so that the drill bit can overshoot without damaging the table.

The table also has holes for drill overshoot as well as weight reduction. A three-jaw chuck is used since three points determine a circle in two dimensions. Four-jaw chucks are rarely seen since offset of the bit is not necessary.

Turning: Engine Lathe
Turning produces solids of revolution that can be tightly tolerances because of the specialized nature of the operation. Turning is performed on a machine called a lathe in which the tool is stationary and the part is rotated. The figure below illustrates an engine lathe.

Lathes are designed solely for turning operations, so that precise control of the cutting results in tight tolerances. The work piece is mounted on the chuck, which rotates relative to the stationary tool.

Turning
Turning refers to cutting as shown below.

The term, 'facing' is used to describe removal of material from the flat end of a cylindrical part, as shown below. Facing is often used to improve the finish of surfaces that have been parted.