Drilling machines (Mechanical Engineering) – The ultimate guide

Drilling machines are one of the most common and important machines in a mechanical tool room. In this post, we will understand a drilling machine’s working principle, its types, and features, and the operations we can perform on it.

What is the working principle of drilling machines?

• The item that we drill into is known as the job.
• In a drilling operation, we place the job on the table. It is stationary throughout the process.
• The cutting tool is inserted into the drill chuck. It is also referred to as the drill tool or the drill bit.
• The drill tool performs two types of motion simultaneously. Linear motion that is downwards in direction. And rotary motion, which is the movement along its own axis.
  • Linear motion: When the drill is fed in the work by giving it a linear motion, the motion is known as a feed motion.
  • Rotary motion: The drill is provided with a rotary motion around its own axis. This motion is known as primary motion.
• Due to the relative motion between the job and the drill, the material gets removed from the job.
• In short, drilling is a cutting operation, to produce a hole in the job.

What are the different types of drilling machines? How are drilling machines classified?

There are six main types of drilling machines that we will be looking at in this course:

1. Portable drilling machine.
2. Upright drilling machine.
3. Sensitive drilling machine.
4. Radial drilling machine.
5. Gang drilling machine.
6. Multi-spindle drilling machine.

How does a Portable drilling machine work?

• The portable drilling machine is small, compact and self-contained. We can carry it anywhere.
• We use it for drilling holes in components too large for transportation, or for drilling holes in positions, where other drilling machines won’t reach.
• The drilling machine attaches to an electric motor. It can work on both, AC and DC power supply.

How does a Sensitive drilling machine work?

• We use a sensitive drilling machine for very light work.
• The work on which a hole is to be drilled is kept on the table.
• The table can be moved up and down along the column and clamped at the desired position using the table clamp.
• A spindle head and drive mechanism (motor etc. are mounted on top of the column.
• The spindle is present inside the head and holds the drill.
• The drill gets its primary motion due to the rotation of the spindle.
• It gets its linear motion by rotating the feed handle manually.
• The spindle speed can be changed by shifting the belt from one pulley to another.
• The machine is called ‘sensitive’ because the operator senses the performance of the drill tool, whether it is jammed or in contact with the work.
• The sensitive drilling machine drills holes with diameters ranging from 1.5mm to 15mm.

How does an Upright drilling machine work?

• The upright drilling machine is similar to the sensitive drilling machine in many ways. However, it is used for heavier work. Moreover, it can be operated automatically.
• A table on which the job is kept, the upright table, is mounted on the column. The column can be either round or box type.
• The table can move along the column using elevating screws.
• The spindle and the power feed mechanism are mounted on top of the column. The spindle makes use of the pulley system to rotate.
• Upright drilling machines have a wide range of speeds.
• Holes up to 50mm in diameter can be made using an upright drilling machine.

How does a Radial drilling machine work?

• We use the radial drilling machine to drill holes in heavy stuff that are hard to move.
• The radial drilling machine is fully automatic. Furthermore, it is highly flexible and mobile.
• The column supports the radial arm, which can be swung to any position over the job. We can raise or lower the radial arm to accommodate jobs of different heights.
• The drill head can slide on the radial arms horizontally. Consequently, all these possible movements enable the drilling of holes in areas that are not easily accessible.
• All of the above movements are handy when the job is too heavy.
• There are three further classifications of a Radial drilling machine:
  • Plane Radial machine: All of the movements that we saw above are possible on the Plane Radial drilling machine.
  • Semi-universal Radial machine: Drill head can be swung along a horizontal axis perpendicular to the arm. Due to this feature, we can drill holes at an angle.
  • Universal Radial drilling machine: We can rotate the drill about a horizontal axis here.

How does a Gang drilling machine work?

• Well, what comes to your mind when you think of the word gang? You aren’t far off.
• These are multiple spindle drilling machines in which the spindles are all in a row.
• Four to six spindles are mounted side by side.
• It is most suitable for jobs where a number of operations such as drilling and tapping are to be carried out in succession.

How does a Multi-spindle drilling machine work?

• Multi-spindle drilling machines also consist of multiple spindles driven by a single motor.
• And all of these spindles are fed into the work simultaneously.
• We can use the Multi-spindle drilling machine to drill a number of holes in the work simultaneously.

What are the different operations that can be done on a drilling machine? What are the different applications of drilling machines?

Here are the different operations that can be done on a drilling machine:

1. Drilling
2. Reaming
3. Boring
4. Counter boring
5. Countersinking
6. Tapping

We can do drilling using a lathe too, what’s the difference between using a lathe and a drilling machine?

Yes, that’s true. As we saw on our guide on lathe machines, we can drill a hole in a job using a lathe machine too. However, the difference is that in a lathe machine it’s the job that is moving. In a drilling machine, it’s the tool that’s moving. Additionally, the lathe is immovable. Hence, it’s practically impossible to drill holes into bigger jobs.

Drilling

• Drilling is an operation in which a cylindrical hole is cut out in the job with the help of a tool known as a drill.
• The job is placed on the table and a revolving drill is fed linearly into the job.
• Material is removed in the form of chips and a hole is produced.

Reaming

• Drilling is not a finishing job. The final output is not a complete product. Hence the hole made after drilling is not accurate.
• Reaming is a process in which the hole is finished. Moreover, a fine surface is achieved.
• A tool known as a reamer removes a very small amount of work from the job.

Boring

• This is a process where holes are enlarged to make seats for nuts, bolts, etc. It’s a finishing job too.
• This process, boring, can correct hole positions and out of roundness.

Counter boring

• In this operation, a pre-drilled hole is enlarged up to a certain depth.
• The job is held firmly, clamps can be used if necessary.
• It is done using the counterboring tool.
• The counterbored hole can be used as a seat for bolts or nuts etc.

Tapping

• Internal threadings are cut inside a previously drilled hole by using a tool known as Tap. This process is known as tapping.
• The tap is held in the spindle and fed to the work. The material is removed from inside the hole.

What are the three cutting parameters of drilling machines?

• Cutting speed: The cutting speed of a drill is nothing but the speed of the point on the circumference of the drill in meters/minute. The speed depends on the type of material to be drilled, tool material and the cutting fluid used. The speed is calculated by the relation:

v = ΠDN/10000 m/min

D => Diameter of the drill in mm.

N => RPM of the drill spindle

• Feed: It is the distance moved by the drill into the work at each revolution of the spindle. The amount of feed depends upon the material being cut, depth of hole, and the type of finish required.
• Depth of cut: This is equal to half of the drilled diameter in millimeters.