Drilling Process
Drilling is a machining process used to create round holes in solid materials by using a rotating cutting tool called a drill bit. The drill bit is pressed against the workpiece while rotating at high speed, which removes material and forms a hole. Drilling is one of the most common operations performed in engineering workshops and manufacturing industries.
The drilling operation is usually carried out on drilling machines, which provide accurate and efficient hole making. Drilling machines are available in different types depending on the size of the workpiece and the nature of the work.
Common Types of Drilling Machines
Bench Type Drilling Machine
A bench drilling machine is a small drilling machine mounted on a workbench or table. It is mainly used for light-duty drilling work on small components. The machine consists of a base, column, table, spindle, drill head, and electric motor.
Features
- Compact and lightweight machine.
- Suitable for small workpieces.
- Easy to operate and maintain.
Uses
- Drilling small holes in metal or wood.
- Used in training workshops and small industries.
Pillar Type Drilling Machine
The pillar drilling machine, also called a column drilling machine, is larger and more powerful than the bench drilling machine. It is mounted on the floor and supported by a vertical column or pillar. This machine is used for drilling medium-sized workpieces.
Features
- Strong and rigid construction.
- Greater drilling capacity than bench type.
- Adjustable table for different heights.
Uses
- Drilling medium-sized metal parts.
- Used in machine shops and fabrication units.
Radial Drilling Machine
A radial drilling machine is designed for drilling large and heavy workpieces. It consists of a radial arm that can rotate around the column. The drill head can move along the arm, allowing holes to be drilled at different positions without moving the workpiece.
Features
- Large drilling capacity.
- Flexible positioning of the drill head.
- Suitable for large and heavy workpieces.
Uses
- Drilling holes in large machine components.
- Used in heavy engineering industries.
Gang Drilling Machine
A gang drilling machine consists of several drilling heads mounted in a row on a single table. Each spindle performs a different operation such as drilling, reaming, or tapping. The workpiece is moved from one spindle to another to perform multiple operations.
Features
- Multiple spindles arranged in sequence.
- Improves productivity.
- Suitable for batch production.
Uses
- Production work in manufacturing industries.
- Performing several drilling operations in sequence.
Multiple Drilling Machine
A multiple drilling machine is designed to drill several holes simultaneously in a workpiece. It uses multiple spindles driven by a single motor.
Features
- Several drill bits operate at the same time.
- High production efficiency.
- Used in mass production.
Uses
- Drilling multiple holes in a single operation.
- Used in automotive and manufacturing industries.
Determination of Tap Drill Size
Before tapping a hole to produce internal threads, a hole of suitable size must be drilled. This hole is known as the tap drill hole. The correct tap drill size ensures proper thread formation and prevents damage to the tap.
Formula for Tap Drill Size
For metric threads:
Tap Drill Size = Major Diameter – Pitch
Example
If the thread size is M10 × 1.5:
- Major diameter = 10 mm
- Pitch = 1.5 mm
Tap drill size = 10 – 1.5 = 8.5 mm
Therefore, an 8.5 mm drill bit should be used before tapping an M10 × 1.5 thread.
Importance of Correct Tap Drill Size
- Ensures proper thread formation.
- Prevents breakage of taps.
- Improves accuracy and quality of threads.
- Reduces tool wear.
Conclusion
Drilling is an essential machining process used for producing holes in engineering components. Different types of drilling machines such as bench type, pillar type, radial, gang, and multiple drilling machines are used depending on the size of the workpiece and production requirements. Proper determination of tap drill size is also important to ensure accurate thread cutting and prevent damage to tools.