Drilling Machine; parts, working principle and safety precautions

 

WORKING PRINCIPLE OF DRILLING MACHINE

It is a machine which is used to drill the holes on the components or workpiece with the help of drilling bits. the drill bits are also called as Multi-point cutting tools which can have rapid impact on the Material Removal Rate (MRR) i.e a single point cutting tool(like the one used in a lathe machine) can removes the material slowly whereas a multi-point cutting tool removes the material at a faster rate and thereby increases MRR. when the power is given to the motor, the spindle rotates and thereby the stepped pulley, attached to it also rotates. on the other end, one more stepped pulley is attached and that is inverted to increase o decrease the speed of the rotational motion. 

Now, a V-belt is placed in between the stepped pulleys so as to drive the power transmission. here a V-belt is used instead of a flat belt, in order to increase the power efficiency.

Now the drill bit also rotates which was placed in the chuck and which was in connection with the spindle. as the pulley rotates, the spindle also rotates which can rotate the drill bit.

Now, by the rotation of hand-wheel, the spindle moves up and down in the vertical direction in order to give the necessary amount of feed to the work and this drill bit is used to make the holes on the component placed in the machine vice.

CONSTRUCTION OF DRILLING MACHINE

The parts are as follows.

1. BASE(BED):

    The base is made up of cast iron which has the capacity of high compressive strength, good wear resistance and good absorbing capacity (i.e absorb the vibrations induced during working condition) and for these reasons, it acts as the base to the drilling machine.

2. COLUMN:

     It is exactly placed at the center of the base which can act as a support for rotating the swivel table and holding the power transmission system.

3. SWIVEL TABLE:

     It is attached to the column which can hold the machine vice in the grips and thereby, the workpiece is fixed in the machine vice to carry out the drilling operation. the swivel table can move up and down by means of rotational motion and can be locked to the column by means of locking nut.

4. POWER TRANSMISSION SYSTEM:

    It consists of motor, stepped pulley, V-belt and the spindle. the power transmission is explained in the working principle of the drilling machine.

5. HAND WHEEL:

    By the rotation of hand-wheel, the spindle moves up and down in the vertical direction in order to give the necessary amount of feed to the wok. here the rotational motion is converted into linear motion by the means of  rack and pinion mechanism.

6. STEPPED PULLEY:

    Two stepped pulleys are present on either side of the column at the top. out of these two, one pulley will be in an upward direction while the other pulley is inverted. always both the pulleys will be there in the opposite direction. the basic function of the stepped pulley is to control the speed of the rotation of the motor.

7. CHUCK:

     Chuck is present at the bottom of the spindle. the basic function of the chuck is to hold the cutting tools firm when cutting is carried out.

  

8. MOTOR:

    The motor is present at the top of the column. the inside motor shaft is there which is connected to a stepped pulley so that we can increase or decrease the speed of the rotation of the motor .

DRILLING MACHINE SPECIFICATION

• The portable Drill machine is specified by the maximum diameter of the drill which can be held.
• Sensitive and the upright drill machine are specified by the diameter of the largest workpiece that can be held.
• The radial drill machine is specified by the length of the arm and column diameter.
• Multiple spindle drill machine is specified by the drilling area, the size and the number of the holes the machine can drill.

                 CUTTING SPEED, FEED, AND MACHINING TIME OF DRILLING MACHINE:

  Cutting Speed:

   The cutting speed can be defined as the speed of the periphery of the cutting tool in meters per minute.

• The cutting speed depends upon the material to be drilled. Generally, the cutting speed varies from 10 to 90 meters/minute.
• The cutting speed for the highspeed drill should be double than that of the carbon steel drill.

 FEED

    The feed can be defined  as the distance moved by each rotaion of the drill bit into the workpiece.

• It is mostly measured in millimeters. the feed range varies from 0.05 to 0.35mm.
• The amount of the metal removed is a function of the cutting speed and the feed.
• By using the highest possible feed rate the best tools life for a given tool can be obtained.                      

 MACHINING TIME:

 The machining time is drilling can be calculated by the following equation:

                T=L/(N x F) minutes.

  

where,

• N= r.p.m of the drill.
• F= feed per revolution of the drill.
• L= length or depth of the hole in mm.
• T= drilling time in minute.

 
  Precautions Which Should Be Followed When Using the Drilling Machine 

1. The machine tool should be strong enough to drill a hole in the workpiece, otherwise, the parts may be deformed due to the cutting force generated. drill feeding arrangement must be directionally stable.
2. To avoid any kind of error it must make sure that the axis of the spindle, adapter, and the tools must coincide.
3. Accurately ground drills should be used so that the uniform chips are produced by both the cutting edges, otherwise, unbalanced forces may deflect the tool during machining.
4. The workpiece must be held rigidly otherwise it may lead to:    

• Error in shape
• Burrs 
• Error in hole location.