Operations of Drilling Machine

 Drilling Machine Operations:

Following are the common types of operations performed on the drilling machine:

 1. Drilling operation

 2. Reaming operation

 3. Boring operation

 4. Counterboring operation

 5. Countersinking operation

 6. Spot facing operation

 7. Tapping operation

1. Drilling:

 Drilling Process

Drilling is that the operation of manufacturing a cylindrical hole by removing metal from the rotating fringe of a cutter called the drill.

The drilling is one among the only methods of manufacturing a hole. Before drilling the centre of the hole is located on the workpiece by drawing two lines at right angles to each other and then a centre punch is used to produce an indentation at the centre.

The drill point is pressed at this centre point to supply the specified hole. Drilling does not produce an accurate hole in a workpiece and the hole location is not perfect.

The internal surface of the hole so generated by drilling becomes rough and the hole is always slightly oversize than the drill used due to the vibration of the spindle and the drill. A 12mm drill may produce a hole the maximum amount as 0-125mm oversize and a 22mm drill may produce one the maximum amount as 0-5mm oversize.

2. Reaming:

Reaming is an accurate way of sizing and finishing a hole which has been previously drilled. In order to end a hole and to bring it to the accurate size, the opening is drilled slightly undersize.

The speed of the spindle is formed half that of drilling and automatic feed could also be employed. The tool used for reaming is understood as reamer which has multiple cutting edges.

Reamer cannot originate a hole. It simply follows the trail which has been previously drilled and removes a really bit of metal. For this reason, a reamer cannot correct a hole location. The material removed by this process is around 0-375mm and for accurate work, this could not exceed 0-125mm.

3. Boring:

 Boring Process

Boring is used for to enlarge a hole by means of an adjustable cutting tool with only one cutting edge. This is necessary where the suitable sized drill is not available or where the hole diameter is so large that it cannot be ordinarily drilled. Used to finish a hole accurately and to bring it to the required size. To machine the interior surface of a hole already produced in casting. Used to correct out of roundness of the hole. To correct the situation of the opening because the boring tool follows an independent path with reference to the opening .

The cutter is held in a boring bar which has a tapered shank to fit into the spindle socket. For perfect finishing a hole, the work is drilled slightly undersize. In precision machines, the accuracy is as high as +0.00125mm. It is a slow process than reaming and requires several passes of the toll.

4. Counterboring:

Counterboring is that the operation of enlarging the top of a hole cylindrically. The enlarged hole forms a square shoulder with the first hole. This is necessary in some cases to accommodate the heads of bolts, studs and pins.

A tool used for counterboring is named a counterbore. The counterbores are made with a straight or tapered shank to fit in the drill spindle. The cutting edges may have straight or spiral teeth.

The tool is guided by a pilot which extends beyond the top of the cutting edges. The pilot fits into the small-diameter hole running clearance and maintains the alignment of the tool.

These pilots could also be interchanged for enlarging different sizes of holes. Counterboring can give an accuracy of about +0.005mm. The cutting speed for counterboring is 25% but that of drilling operations.

5. Countersinking:

Countersinking is the operation of making a cone-shaped enlargement of the end of a hole to provide a recess for a flat head screw or countersunk rivet fitted into the hole.

The tool used for countersinking is named a countersink. Standard countersinks have 60, 82 or 90 inclined angle and therefore the cutting edges of the tool are formed at the conical surface. The cutting speed in countersinking is 25% but that of drilling.

6. Spot facing:

Spot facing is that the operation of smoothing and squaring the surface around a hole for the seat for a nut or the top of a screw. A counterbore or a special spot facing tool could also be employed for this purpose.

7. Tapping:

 Tapping Process

It is the operation of cutting internal threads by means of a cutter called a faucet. Tapping during a drilling machine could also be performed by hand or by machine. A tap could also be considered as a bolt with accurate threads cut thereon. The threads act as cutting edges which are hardened and ground. When the faucet is screwed into the opening it removes metal and cuts internal threads which can fit into external threads of an equivalent size.