DRILLING: DRILL SIZE AND SPECIFICATIIONS, TYPES OF DRILLING MACHINES, PORTABLE DRILLING MACHINE, SENSITIVE OR BENCH DRILL, UPRIGHT DRILLING MACHINE, UPRIGHT DRILLING MACHINE, RADIAL DRILLING MACHINE

DRILLING

Drilling is an operation to produce holes in a solid metal by means of a revolving tool called drill. The drilling is followed by reaming for dimensional accuracy and fine surface finish by means of a multi-tooth revolving tool called reamer.

Boring is the operation for enlarging an existing hole previously produced through drill, cast, punched or by any other suitable operation.

The operations of drilling, boring and reaming can be performed both by hand feed as well as power feed on a large number of machines such as centre lathe, drilling machine, boring machine, turning mill(vertical lathe) Capstan and Turret Lathes, Automatic Lathes etc.

DRILLING MACHINES

DRILL SIZE AND SPECIFICATIIONS:

According to the Indian standards the drills are specified by their diameters, series they belong to, the material they are made of and the IS number. These data are mainly based on the material for which the drill is to be normally used. They are made in 3 types:

1. Type-N → For normal low Carbon Steel.

2. Type-H → For hard materials.

3. Type -S → For soft and tough materials.

Example: 

A twist drill specified as “9.50 IS: 5101 HS” means a twist drill of 9.50mm dia. Confirming to IS: 5101 made of high speed steel unless otherwise mentioned in the tool designation the type should be taken as ‘N’ and the point angle as 1180.

In metric sizes the drills are normally manufactured in diameters ranging from 0.2mm to 10mm.

TYPES OF DRILLING MACHINES:

Drilling machines are manufactured in various sizes and varieties to suit the different types of work. They are broadly classified as:

1. Portable drilling Machine. 

2. Sensitive or Bench drill.

3. Upright drilling Machine (Single Spindle) 

4. Upright drilling Machine (Turret Type)

5. Radial drilling Machine 6. Multiple spindles drilling Machine.

7. Deep hole drilling Machine 

8. Gang drilling Machine.

9. Horizontal drilling Machine 

10. Automatic drilling Machine.

1. PORTABLE DRILLING MACHINE:

It is a very small, compact and self-contained unit carrying a small electric motor inside it. It is very commonly used for drilling holes in such components that can’t be transported to the shop due to their size or weight. 

On account of the high speeds available considerable time is saved. Another advantage is that the holes can be drilled at any desired inclination. Portable drills have a capacity to drill holes up to max. of 18mm dia.

2. SENSITIVE OR BENCH DRILL:

This type of drill machine is used for very light work. Its construction is very simple and so is the operation. No gears are used in the drive. It can be swung to any desired position. 

Vertical movement to the spindle is given by the feed handle through a rack and pinion arrangement. The max. dia. it can drill is 20 mm dia steel.

3. UPRIGHT DRILLING MACHINE (SINGLE SPINDLE):

It is used for heavier work and has a back gearing arrangement. It differs from sensitive drill in its weight, rigidity, application of power feed and wide range of spindle speeds. 

The drilling capacity is up to 75mm in steel. The table can swung to any position with rotary movement. It enables any part of the surface to come under the tool without disturbing work.

4. UPRIGHT DRILLING MACHINE (TURRET TYPE):

It is a production drilling machine and is very useful when a series of different size holes are to be drilled repeatedly or number of different operations like drilling, reaming, counter boring, counter sinking, spot facing etc are to be performed in sequence repeatedly. The turret head which carries six, eight or ten different tool mounting positions is mounted on a ram. It can be easily indexed to bring the proper tool in operating position over the work and can be raised or lowered by moving the ram upwards or down wards. 

The required tools are mounted in sequence in the turret head so that they automatically come in operating position when the head is indexed. This type of machine eliminates tool changing time and a single machine can be used to perform no. of different operations one after the other.

5. RADIAL DRILLING MACHINE:

This machine is very useful because of its wider range of action. Its principal use is in drilling holes on such work which is difficult to be handled frequently. In this the tool is moved to the desired position instead of moving the work for drilling.

Based on the type and number of movements possible, the radial drill can be broadly grouped as:

RADIAL DRILLING MACHINE



i. Plain Radial drill: 

Three principal movements are possible in this type of machine. Viz. vertical movement of the arm along the column, horizontal sliding movement of the drilling head or spindle head along the arm and radial swinging of the arm in horizontal plane.

ii. Semi-Universal Radial drills: 

These machines in addition to the above three basic movements, carry provision for swinging of spindle head about horizontal axis which is normal to the arm. Thus the head, hence the spindle can be inclined to a suitable angle with its normal vertical position on either side, enabling drilling of holes at desired inclination with the normal vertical position.

iii. Universal Radial drills: 

In this machine, the arm itself can be rotates through a desired angle along horizontal axis. This is in addition to the four possible movements available on a semi-universal machine. Thus this machine is highly versatile and facilitates drilling at any desired inclination and location. It is normally provided with a geared drive.

6. MULTIPLE SPINDLES DRILLING MACHINE:

These machines are mostly used in production work and are so designed that several holes of different sizes can be drilled simultaneously increasing the production with sufficient accuracy. In these two or more spindles are driven from a common driving shaft through worm and worm gears or belts. 

Drill heads with a capacity to drive up to 50 spindles simultaneously are available. In these heads it is possible to adjust the spindles to several different positions to enable drilling of holes at any location within the area covered by the head.

7. DEEP HOLE DRILLING MACHINE:

Where very long holes of relatively smaller diameter are required to be drilled these machines are used, such as in rifle barrels and long spindles. These machines can be horizontal as well as vertical types, according to the requirements. These machines are provided with head stock and a carriage. 

The work is mounted between these two and the carriage carries the drill. On the head stock side, the work is supported on a spindle which also rotates the same as the drill is fed slowly.

In deep hole drilling operation, the work rotates at high speed, while the drill is fed in to the work at low speed and feed. Since the drill is quite long it is required to be supported, so is the case with the work piece, for which steady rests are used. Coolant is simultaneously fed to the cutting edges through the passages and it will cool the cutting edges and takes away the chips along with it. 

The drill is withdrawn each time it has cut through a length equal to its diameter. This helps in easy removal of the chips from the hole. Horizontal designs are used for longer jobs and vertical designs are used for relatively shorter jobs.

8. GANG DRILLING MACHINE:

It is a multiple spindle drilling machine and all the spindles are arranged in a row. These spindles are driven either separately or collectively. 

This machine is very useful when the nature of work is such that a number of operations like drilling, reaming, counter boring and tapping etc are to be performed in succession on it. 

The work moves from one spindle to the other, after each operation. The number of spindles depends upon the type of production. Four spindles are very common. One operator can perform all the operations.

9. HORIZONTAL DRILLING MACHINE:

All drilling machines, except one variety of deep hole drilling machines, are of vertical type. In these machines the spindle and the tool are in horizontal position and are mainly used for long jobs, such as columns pipes and barrels etc which are difficult to be drilled in vertical position. 

The horizontal drilling is also used for jobs of excessive weight and extraordinary large size jobs which can’t be handled easily. The operation of drilling performed by keeping the job stationery and moving the machine.

10. AUTOMATIC DRILLING MACHINE:

These are production machines arranged in series to perform a number of different operations in sequence at successive work stations. The work pieces, after completion of an operation at one station, are automatically transferred to the next station for another operation. 

The operation sequence, related cutting speeds, feeds, start and finish of the operation at each station etc are so arranged and synchronized that once the work piece is loaded at the first station, it automatically switches on to the next operation and unloaded.

Several different operations like drilling. boring, tapping, milling, honing etc can be performed on a job is succession on these machines.

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