How Power Drills Work

The power drill is remarkably easy to use, so it makes sense that it's a remarkably simple machine. Basically, a squeeze of the trigger turns on the electric motor, which then rotates the drill or screwdriver bit. However, advancements in drill design and control mean there's a little more to it than that.

The first thing you need to know about power drills is how they're powered. Current models are both corded and cordless; corded drills are rated in amps, while cordless drills are measured in volts. The higher the amperage or voltage a drill has, the more power it has. More power creates more torque, or rotational force, on the drill or screwdriver bit.

A trigger switch, located in the same place you might expect the trigger of a pistol, gets the drill moving. Today's drills usually have a variable speed trigger, meaning that the harder you squeeze, the faster the electric motor spins the drive shaft. Cheaper models run at a single top speed, but pricier models offer between two and four maximum speed settings, usually ranging between 200 and 2,000 rpm. With a variable speed trigger and multiple speed settings, you can operate your drill between zero rpm and the top speed of each setting.

From the electric motor, the drive shaft transmits the rotation through the clutch, which regulates the drill's torque. Many drills have an adjustable clutch, some with as many as 24 settings. The higher the clutch setting, the higher the torque a drill puts out. When the drill reaches the preset clutch setting, the clutch disengages the drive shaft, allowing the motor to turn but not the drill or screwdriver bit. This results in a clicking sound.

The last major part of a drill is the chuck, a mechanism into which you fasten the drill or screwdriver bit. Until the 1980s, chucks were keyed, meaning you needed a special tool to tighten them. Today, nearly all drills are keyless. The gear once tightened by a key is fitted with a grip, allowing the user to secure the bit by hand.

Read on to learn about selecting the right drill or screwdriver bit for the job, and discover ways in which you might not have thought to use power drills.

Of course, a power drill is useless without accessories. These pieces, which are designed to fasten into the chuck, can accomplish a surprising number of tasks. The most common kinds of accessories are drill and screwdriver bits.

Drill bits, like the drills that turn them, come in a variety of shapes and designs. The most versatile of these is the twist bit, a cylindrical shaft with a cutting edge wrapped around it like stripes on a candy cane. These bits typically range in size from 1/64 inch to 1/2 inch and are commonly used to bore holes in wood and metal. Spade bits are the cheapest and most effective way to drill larger holes in wood. The sharp, flat end of these bits is able to scrape away the surface of the wood as it cuts, creating holes between 1/8 inch and 2 inch in size. Brad point and Forstner bits are specially designed to drill cleaner and more precise holes, but they're generally more expensive than twist and spade bits. Drilling holes in concrete or masonry requires special tungsten-carbide-tipped bits; impact drills are especially well-suited for this task.

There are also many different types of screwdriver bits. Phillips head bits are the most common, as these kinds of screws are used extensively in construction and home improvement applications. Other kinds of screwdriver bits include flat head, torque, spanner, tri-wing, hex and torx. Each is a variation on a simple concept: the bit is shaped to fit into a corresponding slot on the head of screw so it can be effectively tightened and loosened.

With the right accessory, drills can emulate almost any tool in the shed. Drum and disc sanding bits can sometimes be used to do the work of much larger and more expensive machines. Other bits can polish, cut or grind materials; larger attachments can even stir paint, mix concrete and serve as a handheld earth auger. Kits are available that harness the power of a drill to create makeshift machines like a lathe or a water pump. While these uses show the incredible versatility of power drills, their specialty is still boring holes and driving screws; they aren't perfect substitutes for the tools they're meant to imitate.

Now that we know all the parts and accessories associated with power drills, let's learn how best to use them.

While power drills have made easy work of boring holes or driving screws, getting it just right can be a bit tricky. By following a few simple steps, you can get quality results on the first try.

With both drilling and screwdriving, the hard part is getting started. Drill bits, especially larger twist bits, have a tendency to wander across the surface of the material when you first start boring. To ensure a precise entry point, first draw cross lines to indicate where you want to drill the hole. Then use a punch -- a small tool used to stamp or pierce objects -- to create a dimple at the intersection of the lines; this will keep your bit in one place as you begin to spin the shaft. Start slowly, then speed up the drill as the hole gets deeper.

Screws have a similar tendency to wander at first. Tapping them in place with a hammer or drilling a small pilot hole before driving them in can help to ensure accuracy. When you're ready to drill, adjust your clutch setting depending on the density of the wood; a high torque setting can cause the screw head to sink in too far or break off completely. If you're loosening or removing screws, a drill's reverse function can be particularly helpful.

While power drills are simple, easy-to-use tools, this doesn't mean that they can't be dangerous if operated improperly. Most manufacturers recommend using eye protection when operating the drill and keeping your hair, clothing, gloves and jewelry away from the drill's moving parts. To prevent fire and electric shock, pay attention to the electrical power source. Inspect cords for damage regularly, and check any replacement batteries to ensure compatibility with the drill and charger. Don't operate corded or cordless drills in the rain or snow.

As with any machine, your drill will last longer if you maintain it well. Most manufacturers recommend using clean cloths to remove dirt, dust, oil, and grease from the drill, while keeping it away from commercial solvents and petroleum-based products, which may damage the plastic casing. Store fully-charged batteries at room temperature, and charge them every month or two when you're not using them. While all batteries eventually wear out, these steps will help lengthen their life.

With so many features and accessories, how do you find the drill that's right for you?

With dozens of models to choose from, deciding which drill to buy can be an overwhelming task. The key is to choose a drill that fits your needs.

One of the first things you need to consider is the drill's power supply. Corded drills never have to be recharged and are often more powerful than their cordless counterparts. But then there's the cord -- it gets in the way and restricts use to jobs near an electrical outlet. Cordless models can be taken almost anywhere but can't run forever. For this reason, it's a good idea to purchase an extra battery so one can charge while the other is in use. Battery voltage ranges from 9.6 to 18; higher voltage commands more torque, but 12- to 15.6-volt models are typically powerful enough for everyday use. High voltage, along with high amp-hour (Ah) ratings, guarantee longer battery life.

But how does the drill actually perform? We've already mentioned a number of features that'll make your home improvement experience more productive and enjoyable. First is the variable speed trigger which allows greater control over the speed of the bit. An adjustable clutch is also important, particularly for driving screws. A drill operating with too much torque has broken many a screw head. It's also important to choose a drill that's right for the tasks for which you plan to use it. One way to determine this is by chuck size, or the size of bit that the chuck can accept. Common sizes are 1/4, 3/8, and 1/2 inch (metric chucks are 6, 8, 10, or 13 mm); the higher the diameter, the higher the torque. For most household tasks, the 3/8 inch (10 mm) chuck diameter provides plenty of torque, but if you plan to drill into more dense materials like metal or concrete, you might consider something a little larger. Finally, you'll have to decide if you want a drill with the impact feature. While this doesn't provide any advantage for drilling holes in wood, it makes screwdriving easier and is necessary for drilling in concrete or masonry.

Another criterion that often gets overlooked is the feel of the drill. When choosing one, pick it up and see how it handles. Is it too heavy? Does it feel balanced in your hand? Is the speed setting easy to adjust with your thumb and index finger?

With these considerations in mind, you'll be ready to get drilling. For lots more information on home improvement, see the links on the next page.