Power drills

Designed to carry out basic drilling operations, the standard mains operated drill will be fitted with a keyed chuck to allow you to change drill bits and a locking switch for continuous drilling without keeping the trigger depressed.  These drills come with electric motors that vary in power output, but generally for DIY purposes a drill with a 550-watt to 900-watt motor will suffice. However, think about the type of work you will be carrying out before deciding on the power of the drill you buy. If you intend using your drill for work on tough materials such as masonry, you will need a more powerful model.

The standard mains-operated drill can be heavy to use particularly if the job entails drilling for a long period of time, so the introduction of the lightweight power drill has been most welcome. This variation of the standard mains-operated drill can be fitted with quite powerful motors but they have much lighter bodies, making them easier to use. These lightweight drills often have a keyless chuck so drill bits can be changed much quicker.

The battery operated cordless drill is possibly the most versatile of all power drills. Operated by a rechargeable battery, the cordless drill is portable and often fitted with reverse rotation so the drill can be used to remove screws. The batteries can range from 9 volts up to about 24 volts with the higher voltage indicating the more powerful drill. To recharge the battery, detach it from the body of the drill and plug it into the mains. Some cordless drills are supplied with two batteries, enabling you to recharge one while using the other. Other features commonly found on cordless drills are:

• Keyless chuck
• Forward/reverse switch to allow the drill to undo screws
• Locking switch for continuous drilling
• Variable speed selector
• Hammer action

The SDS (Special Drive System) hammer drill can be mains-operated or cordless. It is a heavy-duty drill that combines a rotary drilling action with a hammer action. A switch allows you to select just the drilling action or just the hammer action or both in operation together. As hammer drills are larger than the standard power drill and the cordless drill, they have a side handle to give better control particularly when drilling into very hard material.

The chuck mechanism on a hammer drill has a different design to other power drills, so that when it grips the drill bit it provides the most efficient hammer action. This means that drill bits made specifically for hammer drills are required.

There are many different types of drill bits, but the three main types are wood, metal and masonry.

Wood drill bits come in many different sizes and lengths and are suitable for all types of timber. Different jobs require a specific drill bit which come in three categories: brad point or dowel bits, auger bits and flat bits.

Recognisable by the small point at the tip of the bit, the brad point or dowel bit is used to cut clean, straight holes.

To accurately drill large, deep holes the auger bit is recommended. These have a pronounced spiralling shaft that comes to a threaded point at the tip.

The flat bit is designed to cut wide holes rather than deep ones. At the tip is a sharp point, the bit then widens to a paddle-shape blade. The sharp point is placed on the wood where the centre of the hole needs to be. As you begin to drill, the point anchors the bit firmly in the wood allowing the paddle-shaped blades to cut the hole accurately. The diameter of the hole the flat bit will cut will be clearly marked on the side of the paddle-shaped blade.

Also known as HSS (high-speed steel) bits, metal bits are - as their name suggests - for drilling holes in metal and are recognisable by their black colour. Metal bits are extremely hardwearing and can be used for drilling wood and plastic, although reserving them for metal will make them last longer.

Masonry bits have tips made from exceptionally hard material e.g. masonry bits made from chrome-vanadium will have tungsten-carbide tips. This allows the bit to cut through any masonry material. Masonry bits vary in colour depending on what they are made from, but sometimes the tip is clearly a different colour to the shaft because of the hardened tip.

In addition to wood, metal and masonry bits there are numerous specialist drill bits designed for specific purposes.

As we mentioned earlier, the chuck mechanism of a hammer drill will be different to other power drills and will need bits made specifically for it. Although looking identical to other drill bits, the part of the bit that fits into the chuck will have noticeable grooves.

This bit is used to give a drilled hole a wider opening so that the screw head will be flush with the surface. It is important to remember that trying to do this after the hole has been drilled can cause the countersink bit to vibrate in the hole, resulting in a damaged recess. To avoid this, make the pilot hole and then drill the recess before drilling the hole.

To eliminate the necessity of changing drill bits when countersinking, there is a drill bit available with an integral countersink function.  Not only is the hole drilled to the correct depth, the opening is enlarged at the same time.

Drill bits for cutting through tiles and glass are spear-shaped with a tungsten-carbide tip. The tip of the spear point pierces the fragile material without cracking it and then widens the hole to the diameter of the tip's base.

Hole cutter drill bits comprise of a short drill bit protruding from the centre of a circular blade.  The tip of the bit drills the pilot hole and anchors the drill in the material you want to cut the hole in.  As you drill deeper, the circular blade bites into the material and begins to cut through it.

As we have seen, some drills can be operated in reverse rotation allowing them to be used as electric screwdrivers. Although it is worth mentioning that for a power drill to be used in this way it should have a variable speed control so it can operate at slow speed. Screwdriver bits are available as slot-head and cross-head (Phillips and Pozidrive).

• Sticking a small piece of insulating tape around the bit will ensure you drill to the correct depth.
• With a pencil, mark the position of the hole on the wall.
• To prevent the drill from slipping on the wall make a small indentation at the position of the hole using a hammer and nail punch.
• Position the tip of the drill bit into the indentation, then keeping the drill at a right angle to the wall start to drill at low speed.
• As the hole is established, increase the speed and continue drilling to the depth indicated by the tape on the bit.
• Having reached the required depth, pull the bit from the hole while it is still rotating at slow speed. If the bit stops rotating while in the hole, it can get stuck.

Power drills are extremely safe to use. But as with all power tools you should be aware of potential hazards.

• Always follow the manufacturer's instructions.
• Always unplug the drill before fitting the bit.
• Remember to remove the chuck key from the chuck before switching the drill on.
• Never use a power drill if the flex is stretched taught from the mains socket: extend the flex with an extension lead.
• Do not use a power drill that has a split or damaged flex.
• Do not lift a power drill by its flex.
• When drilling it is a good idea to wear goggles or safety spectacles to protect the eyes from flying debris.
• If using a powerful drill or if you are drilling for a long period of time, wear ear protectors.
• When drilling into masonry that produces a large amount of dust, wear a dust mask.