What are the operations carried out by Drilling Machine?

Though drilling machine is designed to make straight and accurate holes, it is used for many other operations. Major operations that are carried out on a drilling machine are explained below:

(a) Drilling. The operation of drilling consists of producing a hole in an object by forcing a rotating drill against it. The same result is carried out in some machines by holding the drill stationary and rotating the work as on the lathe.
(b) Boring. It is the operation of enlarging a hole that has already been drilled or bored with a single point tool. It also rectifies the error of drilling, if any.

(c) Counter Boring. It is the operation of enlarging one end of a drilled hole. The enlarged hole is connected to the original one and it is flat at the bottom. It is done to set bolt head and nuts below the surface.

(d) Spot Facing. To finish off a small surface around a drilled hole is known as spot facing. It is carried out to give a proper seating to bolts and nuts.
(e) Counter Sinking. The top of the drilled hole is beveled to accommodate the conical seat of a flat head screw and counter sunk rivets; the operation is called counter sinking.
(f) Reaming. It is the operation of enlarging a machined hole to proper size to a smooth finish. A reamer is an accurate tool and is not designed to remove much metal.  Allowance for reaming should not exceed 0.015 inches.

(g) Tapping. It is the operation of forming internal threads by means of a tool called tap. To withdraw the tap, the arrangement is made by either a reversible motor or tapping attachment.

(h) Trepanning. It is the operation of producing a hole by removing metal along the circumference of a hollow cutting tool. This operation is performed for producing large holes. Fewer chips are removed and much of the material is saved while the hole is produced.
(i) Grinding. This operation may be performed in a drilling machine to finish a hardened hole. The grinding wheel is made to revolve with the spindle and is fed up and down. A suitable grinding wheel may be selected for surface grinding operation. Grinding can also be done to correct out of roundness of the hole. The accuracy in grinding operation is quiet high about ± 0.0025 mm.
(j) Lapping. It is the operation of sizing and finishing small diameter hole already hardened by removing a very small amount of material by using a lap. There are many kinds of lapping tools. The copper head laps are commonly used. The laps fit in the hole and are moved up and down while it revolves.

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