BORING OPERATION: TYPES, MACHINES & TOOLS

BORING OPERATION

 Boring operation on a lathe machine
Fig. 1 Boring operation on a lathe machine

Boring is the process of enlarging a hole that has already been drilled or cast .
It is the first step to make any kind of holes.
For greater accuracy of the diameter of a hole, this process is used .
It can be used to cut a tapered hole.
It can look like the internal-diameter counterpart to turning, which cuts external diameter.
Small workpiece boring operation can be performed on lathe machines.
And large workpiece boring operation should be performed on boaring mills.
It is possible to perform many operation like turning, grooving, facing, chamfering, etc.

TYPES OF BORING

Boring methods are used for new inventions .
Suppose at greater depth, where direct methods fail there we can use boring operation.

TYPES:

  1. DISPLACEMENT BORING

This method is the combination of sampling and boring operation.
Up to the desired depth closed bottom sampler, slit cup, or piston type is forced in to the ground.

FEATURES :

It is a simple economic method if caving does not occur more.
In this method, there are 25 mm to 75 mm depth holes.
By penetration resistance, major changes of soil character can be detected .

  1. WASH BORING

Because of using limited equipment it is most popular method .
Use of inexpensive and easily portable handling and drilling equipments are the advantage of this process.
In this type, first an open hole is formed on the ground so that the soil sampling or rock drilling operation can be done below the hole.
“Dheki” operation is used in India.
In that, the pipe of 5 cm diameter is put vertically and filled with water using horizontal lever arrangement and by the process of suction and application of pressure, soil slurry comes out of the tube and pipe goes down.

  1. AUGER BORING

For the purpose of large to small holes this method is fast and economical, using simple, light, flexible and inexpensive instruments .
This can be used to determine ground water table.
Auger boring is more comfortable for soft to stiff cohesive soils.

  1. ROTARY DRILLING

In the highly resistant strata the rotary drilling is useful .
Rotary drilling is used to find out the rock strata and also to access the quality of rocks from cracks, fissures and joints.
This method is similar to wash boring technique, because in this bore holes are advanced in depth by rotary percussion.
Rotary drilling is similar to wash boring technique.
In this heavy string of the drill rod is used for choking action.
Drilling mud is slurry of bentonite in water.
Because of higher specific gravity as compared with water and partly due to formation of mud cake on the sides of the hole.
The drilling fluid causes stabilizing effect to the bore hole partly.
In most of the rocks rotary drilling is more comfortable for boring holes of diameter 10 cm or more, preferably upto 15 to 20 cm.
Below 10 cm diameter holes rotary drilling is uneconomical.

  1. CONTINUOUS SAMPLING

Other than any method, continuous sampling gives more reliable and detail information on soil condition.
For preventing the caving in soils, the casing is used.
Because of this continuous sampling is used extensively in detailed and special foundation exploration for important structures.
This method is slower & more costly than intermittent sampling.
For advancing larger diameter borings in stiff and tough strata of clay and mixed soil the continuous sampling is used .
Also when modern rotary drilling rigs or power driven augers are not available then continuous sampling is used.

BORING MACHINES

Horizontal boring machine
Fig. 2 Horizontal boring machine
Vertical boring machine
Fig. 3 Vertical boring machine

In 1775, John Wilkinson invented the first machine tool.
Now these machines are discover in a large variety of sizes and styles.
Workpieces are commonly 1 to 4 metres (3 ft 3 in to 13 ft 1 in) in diameter, but can be as large as 20 m (66 ft).
The dimensions between the workpiece and the tool bit can be changed about two axes to cut both vertically and horizontally into the internal surface.
By the hollow passageway through the boring bar where coolant can flow freely, cooling of the bore is done.
For holding of cutting tool, the bar is the protruding arm of the machine.

BORING TOOLS

In this operation, a hole is created with a tool called a bit. Holes of 6 mm size or larger are bored. Holes of 6 mm size or smaller are drilled. It is the first step in making any kind of shaped opening or making holes.

TYPES OF BORING TOOLS:

Countersunk bit
Fig. 4 Countersunk bit
Auger bit
Fig. 5 Auger bit
  1. Hand operated drills
  2. Machine operated drills
  3. Twist drill
  4. Countersunk
  5. Brace
  6. Auger bit
  7. Bit gauge

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