Professional and consumer power drills perform well and are excellent values — but don't expect a consumer tool to perform like a professional.

Can you recognize the differences between a consumer drill the do-it-yourself buyer uses and the professional type an electrician uses daily to make a living? A quick answer is: The professional power tool is designed to be more powerful, last longer, and perform better under stress than its consumer counterpart.

The differences are strictly of function and design. The professional- and consumer-type drills do the jobs they were designed to do extremely well. But, they're intended for different applications. You might compare their differences with those of a dump truck and pickup truck. Both are made to haul things, but under different circumstances and conditions. In other words, the higher the performance or the more specialized the machine, the more it's going to cost. But to say one is better than the other is irrelevant. The same is true for professional and consumer power drills.

The cord. One of the specific differences between a consumer-type drill and a drill for the professional who uses it on the job eight hours a day is the electrical cord. On the consumer tool, it's rare the cord is longer than 6 ft. That's not a major inconvenience because home owners don't typically consider it an imposition to use an extension cord.

But the professional tool has a cord that's usually a minimum of 8 ft long (frequently 10 ft) because anything less would not permit work at ceiling height without an extension cord.

Cord materials are also different. For this professional tool, cords are natural rubber or synthetic elastomer that remain flexible in cold weather. While the professional works in cold weather, the consumer rarely works well outdoors in extreme conditions. For this reason, the consumer tool has a cord jacket made of PVC material less expensive and less flexible at lower temperatures.

Both tools have a bulky fitting called the "cord protector," where the tool and the cord join. It guards the cord against bending at a severe angle and possibly damaging the wires inside. On the consumer tool, the cord protector is molded onto the cord. But on the professional or heavy-duty drill, the cord slips through the cord protector. If the cord is damaged, repairing involves disconnecting the cord inside the tool, pulling it through the cord protector, and discarding it. Then, the repair person must insert a new piece of cable through the cord protector, connecting it to the contacts inside the tool.

The switch. Dusty environments and switch usage creates a difference between switches used on professional tools and those on consumer tools.

On any jobsite, there are fine particles flying around, such as the residue from drilling into concrete or drywall, which can ruin a switch. So, the switch mechanism on heavy-duty tools is specially protected.

The professional user generally turns the tool on and off all day long. That continuous use puts stress on the switch. Thus, the manufacturer designs the switch to withstand up to several hundred work-hours of constant use. By contrast, the do-it-yourself buyer seldom uses the switch on a power tool for more than a few work-hours over the life of the tool.

The motor. A heavy-duty tool's motor has to handle a greater workload than a consumer tool, so it must generate more power. It not only must withstand, but also sustain overloading for long periods to avoid burning up.

In any discussion of a power tool's motor, an item of major importance is the ratio of power-to-weight and the power tool's physical dimensions. The professional has to carry the drill around all day and use it overhead or at arm's length. The lighter and smaller it is, the easier to use for an entire 8-hr shift. So, whatever weight and bulk can be eliminated makes the tool easier to manipulate.

Manufacturers are now improving the power-to-weight ratio with computer-aided motor designs that are more efficient, lighter than previous motors, yet just as powerful. They are also using lighter weight magnesium instead of heavier aluminum castings.

Commutators. In a consumer drill armature or rotor, there are the same number of copper bars on the commutator as there are slots in the lamination stack through which the coils of wire are wound. One coil of wire can be wound in each lamination of the consumer tool.

In a professional-grade tool, there are usually twice as many copper bars on the commutator as there are slots in the lamination stack. This makes it possible to wind two independent coils of wire in each lamination slot of a professional-grade tool. This difference in construction results in much less arcing at the commutator bar/carbon brush interface. Reducing the amount of heat-generating electrical arcs prolongs the life of the brushes, commutator, and motor.

Brush placement also is important to reduce arcing. In consumer and heavy-duty tools, two brushes ride directly on the copper commutator bars. In professional tools, reduced arcing is accomplished by more precise positioning of the brushes. To do this, very often a brass holder having very tight tolerances is used for the brushes. This assures a more consistent positioning of the brushes in relationship to the copper bars of the commutator.

Heat and electrical motors. For around-the-house use, not much power is required from a power tool. But on the jobsite, motors of a heavy-duty power drill must withstand high temperatures and continue to run.

To fight heat in an industrial-type power drill's electric motor, once the wire is wrapped around the commutator and the armature, resin is applied to the windings. By capillary action, the resin finds its way into the coils and coats every wire. That resin has the effect of bonding the wires together into a solid unit so that under high temperatures and high speeds, one w ire doesn't rub against another and short circuit.

The resin also helps guard against dust and grit. In many heavy-duty tools, another layer of tape or other coating is added to keep abrasives from wearing away the wire insulation.

Bearings. As noted previously, the armature in a portable electric power tool spins at about 25,000 rpm to 30,000 rpm. That's a very high speed, and it causes vibration and lateral movement between the commutator and brushes. If that motion is too great, it creates excessive arcing. This arcing kills brushes and creates heat that kills the motor. Bearings serve to limit the play between the brushes and commutator.

Basically, three different types of bearings are used in portable power tools: Ball bearings, roller bearings, and powder-metal sleeve bearings. In a heavy-duty tool, ball bearings are used because they control play to distances measured in ten-thousandths (.0001) of an in. This tight control of radial clearance minimizes the relative radial motion between the commutator and the brushes, thus reducing arcing.

One of the more highly loaded bearings is the one on which the chuck spindle rides. When drilling with hole saws, spade bits, and even twist drills, that particular bearing is often subjected to very high side loads, as well as very high fore and aft loads. For this reason, in a professional-grade tool, a ball bearing that can withstand those loads is used to support the chuck spindle.

Consumer tools use some ball bearings, but they use sleeve bearings more extensively. Again, it's a matter of relative cost. To put a ball bearing in a consumer tool would be like putting a diamond movement in what is otherwise an inexpensive watch.

Gears. Heavy-duty tools usually have gears of wrought steel that are heat-treated after machining. Heat treating hardens the metal. But don't confuse hardness with brittleness. Hardness means toughness and allows a heavy-duty tool to withstand the overloading it often receives.

As for consumer tools, powder-metal gears are frequently used. Powder-metal gears are made using a sophisticated technology where tiny granules of ground-up metal are placed in a mold, compressed under very high force, and heated until they solidify. Gears made by this process usually require no machining, which is one of the largest cost factors in wrought-steel gears. But don't think of powder metal as being second-rate material; it isn't. The increase in sophistication of the technique is such that soon nearly all gears will probably be made of powder metal. But today, powder-metal gears are less expensive than gears machined from wrought steel.

The chuck. Most people think the most expensive part of a drill is the motor; however, often it's not. Instead, the chuck is one of the most expensive components. On a professional tool, the jaws; the part of the chuck that grasps the drill bit; are made of costly steel, case-hardened for durability. The reason is simple: Think of the number of times you insert and remove a bit from the jaws of a heavy-duty tool. When you consider the few times that's done with a consumer tool, it's easy to see why a heat-treated, less expensive variety of steel is used for their chucks.

The professional chuck provides an advantage. The "run out" factor is precisely 2-to-1. You could call that the "wobble factor." The departure of the bit from a straight line measures at a distance of 1 in. from the jaws. In a consumer tool, a wobble of 10 one-thousandths (.010) of an inch is accepted. But on a professional tool, the permitted variance is no more than five one-thousandths (.005) of an inch; only half as much. That's a function of more precise machining.

The housing. People often associate plastic with cheapness. Plastics used on heavy-duty tools generally cost at least as much as, and in many cases more than, comparable metal parts. Plastics are used not to save money, as some people think, but rather because they do a better job than most metals and are safer than metals, because they are much better electrical insulators.

There is a difference between the plastic used in a heavy-duty tool and the kind used in a consumer tool. Some parts of heavy-duty tools are molded of a supertough nylon. This material is almost indestructible. Some aluminum castings have failed (not easily) during tests.

For consumer tools, a good plastic is used, but not a supertough nylon. A couple of reasons describe why. First, a professional may drop the tool out of a window or toss it into a corner a couple of feet away. A consumer typically doesn't do that. Second, professional tools are often used around grease and solvents. Supertough nylon will resist the effects of corrosives. Third, heat is always a consideration. So, special nylon and other plastics used in heavy-duty tools can withstand high operating temperatures. A consumer tool doesn't get that hot.

Tool assembly. What also makes a difference in drills is the manner in which they are assembled. As was previously mentioned when discussing bearings and wobble, the alignment of a drill is extremely important. That same alignment is important in a heavy-duty drill to increase its efficiency and prolong its life. So the tool is put together in a different way than a consumer tool.

For purposes of illustration, assume there are three different external parts on a drill: The gear housing, the motor housing, and the handle. They have to be joined into a single unit. A heavy-duty drill is assembled like a Chinese puzzle; everything interlocks. Where each of these three parts comes together, pilot pins are used to set the alignment. Then separate sets of screws join the first part to the second, and the second to the third. It's a rigid and well-integrated structure. Drop it, and it will stay pretty much in line.

In a consumer drill, just one set of screws is used. They go from the gear case, through the motor housing, into the handle. With this assembly, there's a greater possibility of misalignment from the axis.

A professional drill is subjected to a lot of hard use on a jobsite. Aside from dust and weather extremes, the tool is likely to be banged, dragged, and dropped; its cord pulled, swung, and twisted. The tool has to be tough to take that kind of treatment. A heavy-duty drill is built for heavy-duty jobs: Its consumer counterpart is designed for less frequent use and a lighter load of work.