Drilling is a metal cutting process carried out by a rotating cutting tool called twist drill to make circular holes in solid materials.
Drilling machine
A power operated machine tool which holds the drill in its spindle rotating at high speeds and when actuated move linearly against the work piece produces a hole.
These are light duty machines used in small workshops. Also called Sensitive drilling machines because of its accurate and well balanced spindle. Holes of diameter 1 mm to 15 mm.
Bench drilling machine
parts
Vertical main column Base Moving drill head Work table Electric motor Variable speed gear box and spindle feed mechanism.
working Work piece with the exact location marked on it with the centre punch is clamped rigidly on the work table. spindle axis and center punch indentation are in same line. Machine is started and drill bit is lowered by rotating feed handle. Drill bit touches the work and starts removing material.
Bench drilling machine
Radial drilling machine
These are heavy duty and versatile drilling machine used to perform drilling operate on large and heavy work piece. Holes up to 7.5 cm.
Radial drilling machine
parts
Heavy base Vertical column Horizontal arm Drilling head
working
Work piece is marked for exact location and mounted on the work table. Drill bit is then located by moving the radial arm and drill to the marked location. By starting drill spindle motor holes are drilled.
Upright/Pillar Drilling Machine This machine is quite similar to the bench drilling machine but of little larger size and higher capacity and is fixed on the floor foundation. This drilling machine is able to take larger drills.
Gang Drilling Machine Each drill head has its own power unit and carries a tool to perform an operation on a job in sequence. DESIGNED FOR MASS PRODUCTION Gang drilling machines are useful when several different machining cuts with different tool are to be taken on sufficiently large number of work pieces.
A Gang drill machine has a number of drill heads arranged with a common base and table. The spindle may be set up with drills of different diameter or other tools as required. The job is moved from one spindle to the other spindle for performing various operations.
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Multi-spindle Drilling Machine
They may be built as specific jobs with their spindles fixed in specific positions or as general purpose machines in which the relative distance between the spindles can be changed within a range.
Multi-spindle drilling machines with two or more spindles driven by a common head. This machine are used for drilling a numbers of holes simultaneously in a work piece. Multi-spindle machines are high production rate machines and lead to considerable saving for large quantity jobs.
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Automatic Drilling Machine After one operation
is completed at one workstation the work piece is automatically transferred to the next work station. Because all operation are done automatically the preciseness is higher and production time is lower.
These are high performance automatic machine designed for variety of operations being done on the work piece. A number of machines are arranged in series to perform variety of different operations on the workpiece at successive work stations.
Drilling It is a process of creating or originating a hole in a solid work piece using a tool called Twist drill.
Reaming
It is a process of smoothing the surface of drilled holes with a tool. Tool is called as reamer. Initially a hole is drilled slightly smaller in size. Drill is replaced by reamer. Speed is reduced to half that of the drilling.
Reaming
Boring
It is process carried on a drilling machine to increase the size of an already drilled hole. Initially a hole is drilled to the nearest size and using a boring tool the size of the hole is increased.
Counter boring
This process involves increasing the size of a hole at only one end. Cutting tool will have a small cylindrical portion called pilot. Cutting speed = twothirds of the drilling speed for the same hole.
Counter sinking
This is an operation of making the end of a hole into a conical shape. Cutting speed = half of the cutting speed of drilling for same hole.
Spot facing
It is a finishing operation to produce flat round surface usually around a drilled hole, for proper seating of bolt head or nut. It is done using a special spot facing tool.
Tapping
Process of cutting internal threads with a thread tool called as tap. Tap is a fluted threaded tool used for cutting internal thread Cutting speed is very slow.
Trepanning
Trepanning is the process for making large holes in sheet metal. A small diameter hole is drilled in center for drilling large diameter hole. The pilot of trepanning tool is fitted into this hole and the length of the adjustable arm is set to the radius of the hole to be cut. Holes up to a diameter of 350 mm can be cut by this arrangement.
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Specification of Drilling machine I) The size of the working table and capacity of the machine. 2) Maximum size of the work piece on the particular machine. 3) Maximum diameter of drill on the particular machine. 4) Number of spindles on the particular machine. 5) Length of arm and column diameter must be specified for radial drilling machine
Specification of a radial drilling machine
Power capacity eg: 1.5 hp for drilling motor and 0.5 hp for elevating motor. The range of speed of spindle eg: 50 to 2800 rpm.
Length of arm on which drill head can traverse. eg: 600 mm. Vertical movement of the arm eg: 500 mm. Angular swing of arm eg: 360˚
Range to which drill bit can reach eg: 350 mm to 900 mm. Drill depth eg: 32 mm for steel.
