1. Drilling

2. Reaming

3. Boring

4. Counter boring

5. Counter sinking

6. Spot facing

7. Tapping


1. Drilling: 

It is the main operation done on drilling machine. It is the operation of producing a circular hole in a solid metal by means of a revolving tool called drill bit.

2. Reaming: 

It is the operation of finishing a hole to bring it to accurate size and have a fine surface finish. The operation is performed by means of a multi- tooth tool called reamer. The operation severs to produce a straight, smooth and accurate hole. The accuracy to be expected is within ±0.005mm.

3. Boring: 

It is an operation used for enlarging a hole to bring it to the required size and have a better finish. It involves the use of an adjustable cutting tool having a single cutting edge. It can be used for correcting the hole location and out of roundness, if any, as the tool can be adjusted to remove more metal from one side of the hole than the other. It is a slower process than reaming. The accuracy to be expected is within ±0.0125mm.

4. Counter Boring: 

The operation is used for enlarging only a limited portion of the hole, is called counter-boring. It can be performed by means of a double tool boring bar or a counter boring tool. In order to maintain alignment and true concentricity of the counter bored hole with the previously drilled hole, the counter boring tool is provided with a pilot at its bottom.

5. Counter Sinking: 

It is the operation used for enlarging the end of a hole to give it a conical shape for a short distance.  This is done for providing a seat for the counter sunk heads of screws, so that the top face of screw matches with the main surface of work. The standard counter sunk carry included angle of 600, 820 or 900.

6. Spot facing: 

This operation is used for squaring and finishing the surface around and at the end of a hole, so that the same can provide a smooth and true seat to the underside of bolt heads or collars etc. This is usually done on castings or forgings. The hole may be spot faced below the rough or above it, i.e on the upper surface of the boss if the same is provided.

7. Tapping: 

It is the operation done for forming internal threads by means of a tapping tool. To perform this operation the machine should be equipped with a reversible motor or some other reversing mechanism. Drill size for taping = 0.08

tapping size. Drill size = tap size – 2

depth of thread.

Leave a Comment