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Basic Operations Related To Drilling Process




Drilling is a cutting process that uses a drill bit to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at rates from hundreds to thousands of revolutions per minute.

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

  • Reaming,
  • Drilling,
  • Boring,
  • Lapping,
  • Tapping,
  • Counterboring,
  • Countersinking,
  • Center drilling, and
  • Spot facing.

These are illustrated in the below shown Figure  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.


Machining operations related to drilling

Reaming:- 
Reaming operation is used to slightly enlarge a hole, to provide a better tolerance on its diameter, and to improve its surface finish.Reaming operation is performed by means of a multi tooth tool called reamer. Reamer possesses several cutting edges on outer periphery and may be classified as solid reamer and adjustable reamer.


Drilling :-
This is the operation of making a circular hole by removing a volume of metal from the job by a rotating cutting tool called drill. Drilling removes solid metal from the job to produce a circular hole. Before drilling, the hole is located by drawing two lines at right angle and a center punch is used to make an indentation for the drill point at the center to help the drill in getting started. A suitable drill is held in the drill machine and the drill machine is adjusted to operate at the correct cutting speed. The drill machine is started and the drill starts rotating. Cutting fluid is made to flow liberally and the cut is started. The rotating drill is made to feed into the job. The hole, depending upon its length, may be drilled in one or more steps. After the drilling operation is complete, the drill is removed from the hole and the power is turned off.


Boring :-
The boring operation where enlarging a hole by means of adjustable cutting tools with only one cutting edge is accomplished. A boring tool is employed for this purpose. 



Lapping :-
This is the operation of sizing and finishing a hole by removing very small amounts of material by means of an abrasive. The abrasive material is kept in contact with the sides of a hole that is to be lapped, by the use of a lapping tool.

Tapping:-
Tapping operation is performed by a tap and is used to provide internal screw threads on an existing hole.


Counter-boring:-
Counter-boring operation provides a stepped hole, in which a larger diameter follows a smaller diameter partially into the hole. A counter-boring  hole is used to seat bolt heads into a hole, so the heads do not protrude above the surface.

Countersinking:- 
countersinking operation is similar to counter-boring, except that the step in the hole is cone-shaped for flat head screws and bolts.
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.

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.

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