Operations Related to Drilling

There are several operations related to drilling. Some of them are:

1. Reaming,
2. Tapping,
3. Counterboring,
4. Countersinking,
5. Center drilling, and
6. Spot facing

These are illustrated in Figure 1 and described in this section. Most of the operations follow the drilling process; a hole must be made first by drilling method, and then the hole is modified by one of the other operations related to drilling. Centering and spot facing operations are exceptions to this rule. All of the operations use rotating tools.

1. Reaming: Reaming operation is used to slightly enlarge a hole, to provide a better tolerance on its diameter, and to improve its surface finish. The tool is called a reamer, and it usually has straight flutes.
2. Tapping: Tapping operation is performed by a tap and is used to provide internal screw threads on an existing hole.
3. Counterboring: Counterboring operation provides a stepped hole, in which a larger diameter follows a smaller diameter partially into the hole. A counterbored hole is used to seat bolt heads into a hole, so the heads do not protrude above the surface.
4. Countersinking: countersinking operation is similar to counterboring, except that the step in the hole is cone-shaped for flat head screws and bolts.
5. Centering: Centering operation also called center drilling, this operation drills a starting hole to establish its location for subsequent drilling accurately. The tool is known as a center drill.
6. Spot facing: Spot facing operation is similar to milling. This operation is used to provide a flat machined surface on the workpart in a localized area.