Drill
A drill is a cutting tool used to produce circular holes in solid materials. It is commonly used in drilling machines and is one of the most important tools in mechanical workshops. The drill rotates at high speed and removes material from the workpiece to form a hole.
Material of Drills
Drills are made from strong and wear-resistant materials so that they can withstand high temperature and cutting forces during drilling operations.
- High Carbon Steel
- High Speed Steel (HSS)
- Alloy Steel
- Carbide Tipped Drills
Among these, High Speed Steel (HSS) drills are most commonly used because they maintain hardness even at high temperatures.
Types of Drills
Taper Shank Drill
The taper shank drill has a tapered shank which fits directly into the spindle of a drilling machine. It is mainly used for drilling larger holes.
Features
- Strong and rigid design
- Used in heavy drilling operations
- Fits directly into machine spindle
Straight Shank Drill
The straight shank drill has a cylindrical shank and is held in a drill chuck. It is commonly used for drilling small and medium sized holes.
Features
- Simple cylindrical shank
- Held in drill chuck
- Used in bench drilling machines
Parts of a Drill
- Shank: The part held in the machine spindle or chuck.
- Body: The main portion of the drill containing flutes.
- Flutes: Spiral grooves that remove chips during drilling.
- Lands: Surfaces between flutes that guide the drill.
- Point: The cutting end of the drill.
- Cutting Edge: The sharp edge that cuts the material.
- Web: The central core of the drill.
Sizes of Drills
Drills are manufactured in various sizes depending on the diameter of the hole required.
- Metric size drills (measured in millimeters)
- Fractional size drills (measured in inches)
- Number drills
- Letter drills
Drill Angles
The angle at the tip of the drill is called the point angle. Different materials require different cutting angles for efficient drilling.
| Material | Recommended Point Angle |
|---|---|
| Soft Materials (Aluminium, Copper) | 90° – 100° |
| Mild Steel | 118° |
| Hard Steel | 130° – 135° |
| Cast Iron | 118° |
Cutting Speed and Feed
Cutting Speed: Cutting speed refers to the speed at which the cutting edge of the drill moves relative to the workpiece.
Feed: Feed is the distance the drill advances into the workpiece during one revolution.
Proper cutting speed and feed ensure smooth drilling, longer tool life, and better hole quality.
R.P.M. for Different Materials
R.P.M. (Revolutions Per Minute) indicates how fast the drill rotates. Different materials require different spindle speeds.
| Material | Recommended RPM |
|---|---|
| Aluminium | High RPM |
| Mild Steel | Medium RPM |
| Cast Iron | Low RPM |
| Brass | Medium to High RPM |
Drill Holding Devices
Drill holding devices are used to hold the drill securely in the spindle of the drilling machine.
Material
These devices are generally made from hardened steel to ensure strength and durability.
Types of Drill Holding Devices
- Drill Chuck
- Drill Sleeve
- Drill Socket
- Drill Drift
Construction
Drill holding devices are designed to firmly grip the drill and transmit the rotational force from the machine spindle to the drill. They ensure proper alignment and accurate drilling.
Uses
- Holding straight shank drills in a chuck.
- Holding taper shank drills in machine spindle.
- Ensuring accurate drilling operations.
- Preventing slipping of drills during operation.
Conclusion
Drills are essential cutting tools used for producing holes in various materials. Understanding drill materials, types, angles, cutting speeds, and holding devices helps ensure efficient and accurate drilling operations in mechanical workshops and manufacturing industries.