Operations Performed on Drilling Machine-Tapping
Operations Performed on Drilling Machine-Tapping: It is the operation of cutting internal threads by using a tool called a tap. A tap is similar to a bolt with accurate threads cut on it. To perform the tapping operation, a tap is screwed into the hole by hand or by machine. The tap removes metal and cuts internal threads, which will fit into external threads of the same size. For all materials except cast iron, a little lubricate oil is applied to improve the action. The tap is not turned continuously, but after every half turn, it should be reversed slightly to clear the threads. Tapping operation is shown in Fig.1. The geometry and nomenclature of a tap is given in Fig. 2.
Fig. 1 Tapping operation
Fig. 2 Geometry and nomenclature of tap
Core drilling: Core drilling operation is shown in Fig. 3. It is a main operation, which is performed on radial drilling machine for producing a circular hole, which is deep in the solid metal by means of revolving tool called drill.
Fig. 3 Core drilling operation
Size of a Drilling Machine: Different parameters are being considered for different types of drilling machines to determine their size. The size of
a portable drilling machine is decided by the maximum diameter of the drill that it can hold. The sensitive and upright drilling machines are specified by the diameter of the largest workpiece which can be centered under the drill machine spindle. A radial drilling machine is specified by the length of the arm and the diameter of the column. To specify a drilling machine completely, following other parameters may also be needed:
1. Table diameter
2. Number of spindle speeds and feeds available
3. Maximum spindle travel
4. Morse taper number of the drill spindle
5. Power input
6. Net weight of the machine
7. Floor space required, etc.
CUTTING SPEED: The cutting speed in a drilling operation refers to the peripheral speed of a point on the surface of the drill in contact with the work. It is usually expressed in meters/min. The cutting speed (Cs) may be calculated as:
Cs = ((22/7) × D × N)/1000
Where, D is the diameter of the drill in mm and
N is the rpm of the drill spindle.
FEED: The feed of a drill is the distance the drill moves into the job at each revolution of the spindle. It is expressed in millimeter. The feed may also be expressed as feed per minute. The feed per minute may be defined as the axial distance moved by the drill into the work per minute. The feed per minute may be calculated as:
F = Fr × N
Where, F = Feed per minute in mm.
Fr = Feed per revolution in mm.
N = R.P.M. of the drill.