A cordless drill is a portable power tool that spins a bit to drill holes or drive screws without being plugged into a wall outlet. It matters because it combines mechanics, electricity, and safety in one common workshop machine. Understanding its parts helps students choose the right speed, torque, bit, and battery for a job.
It also helps prevent stripped screws, broken bits, damaged materials, and injuries.
Key Facts
- Rotational speed is often measured in revolutions per minute, rpm.
- Torque is twisting force, and higher torque is useful for larger screws or harder materials.
- Power can be estimated by P = τω, where P is power, τ is torque, and ω is angular speed.
- Battery energy is E = V × Ah, where V is voltage and Ah is amp-hours.
- Drill bit surface speed increases with bit diameter at the same rpm, so large bits usually need lower speed.
- The clutch limits torque by slipping when resistance is too high, helping prevent overdriving screws.
Vocabulary
- Chuck
- The chuck is the adjustable clamp at the front of the drill that grips the drill bit or driver bit.
- Clutch
- The clutch is a torque control mechanism that slips when the set twisting force is reached.
- Trigger switch
- The trigger switch controls the drill motor and often changes speed based on how far it is pressed.
- Lithium-ion battery
- A lithium-ion battery is a rechargeable power source commonly used in cordless drills because it stores high energy in a compact pack.
- Gearbox
- The gearbox uses gears to trade speed for torque or torque for speed depending on the selected setting.
Common Mistakes to Avoid
- Using the wrong bit for the material, which can overheat the bit, tear the workpiece, or make the drill slip.
- Running a large bit at maximum speed, which is wrong because larger diameters create higher cutting speed and more heat at the edge.
- Ignoring the clutch setting when driving screws, which can strip screw heads, sink screws too deeply, or damage soft material.
- Holding the drill at an angle when a straight hole is needed, which causes crooked holes and can snap small bits under side load.
Practice Questions
- 1 A cordless drill battery is rated 18 V and 2.0 Ah. Estimate the battery energy in watt-hours using E = V × Ah.
- 2 A drill motor delivers 4 N·m of torque at an angular speed of 25 rad/s. Calculate the mechanical power using P = τω.
- 3 Explain why a drill might use a low-speed, high-torque gear for driving a long screw into wood but a high-speed setting for drilling a small pilot hole.