Drilling Machine Operations: Drilling, Reaming, Boring, Counter boring, Countersinking, Spot facing, Tapping, Lapping, Grinding, Trepanning

Drilling Machine Operations:-

· The different operations that can be performed in a drilling machine are:

Ø Drilling

Ø Reaming

Ø Boring

Ø Counter boring

Ø Countersinking

Ø Spot facing

Ø Tapping

Ø Lapping

Ø Grinding

Ø Trepanning

Drilling:-

· Drilling is the operation of producing a cylindrical hole by removing of metal by the rotating edge of cutting tool called the drill.

· The drilling is the simplest method of producing a hole.

· Before drilling, the centre of hole is located on the workpiece by drawing two lines at right angles to each other and then center punch is used to produce an indentation at the centre.

· Drill point is pressed at this centre point to produce the required hole.

· Drilling does not produce an accurate hole in a workpiece and the hole is generated by drilling becomes rough and the hole is always slightly oversize than drill used due to vibration of the spindle and drill.

· A 12 mm drill may produce a hole as much as 0.125 mm oversize and 22 mm drill may produce 0.5 mm oversize.

Drilling

Reaming:-

· Reaming is an accurate way of sizing and finishing a hole which has been previously drilled.

· To finish a hole and to boring it to the accurate size, the hole is drilled slightly undersize.

· The speed of spindle is made half of drilling and automatic feed may be produced.

· Reamer tool is used which has multipoint cutting edges.

· It can not originate hole, it simply follow the path which has been previously drilled.

· The material removed by this process is around 0.375 mm and for accurate work it should not exceed 0.125 mm.

Reaming

Boring:-

· Boring is performed in a drilling machine for reasons stated as under.

1. To enlarge a hole by means of an adjustable cutting tool with only one cutting edge.

2. To finish a hole accurately and to bring it to the required size.

3. To machine internal surface of a hole already produced in casting.

4. To correct out of roundness of the hole.

5. To correct the location of the hole as the boring tool follows an independent path with respect to the hole.

· In precision machine the accuracy is as high as ± 0.00125 mm.

Boring

Counter boring:-

· Counter boring is the operation of enlarging the end of hole cylindrically.

· The enlarged hole forms a square shoulder with original hole.

· This is necessary in some cases to accommodate the heads of bolts, studs and pins.

· Counter boring can give accuracy of about ± 0.050 mm.

· The cutting speed for counter boring is 25% less than that of drilling operation.

Counter boring

Countersinking:-

· Counter sinking 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.

· Standard countersinks have 60^o, 82^o or 90^o inclined angle.

· Cutting speed is 25% less than that of drilling.

Counter sinking

Spot facing:-

· Spot facing is the operation of smoothing and squaring the surface area and a hole for the seat for a nut or the head of the screw.

· Counter bore or a special facing tool may be employed for this purpose.

Spot facing

Tapping:-

· Tapping is the operation of cutting internal threads by means of a cutting tool called a tap.

· Tap may be considered as a bolt with accurate threads cut on it.

· The threads act as cutting edges which are hardened and ground.

· When tap is screwed into the hole it removes metal and cuts internal threads which will fit into external threads of the same size.

Tapping

Lapping:-

· Lapping is the operation of sizing and finishing a small diameter hardened by removing a very small amount of material by using a tap.

Grinding:-

· Grinding operation may be performed in a drilling machine to finish a hardened hole.

· Grinding wheel is made to revolve with the spindle and is fed up and down.

· Accuracy in grinding operation is ± 0.0025 mm.

Trepanning:-

· Trepanning is the operation of producing a hole by removing metal along the circumference of a hollow cutting tool.

· Trepanning operation is performed for producing large holes.

· Fewer chips are removed but tool may be operated at higher speeds as the variation in diameter of tool is limited by narrow cutting edge.

Trepanning