Quality in power tools is determined by physical construction and motor capacity. A light-duty unit might be satisfactory for a casual user, but it would have an extremely limited life in heavy-duty applications.
Quality housings are usually die-cast aluminum, high-impact plastic or a combination. Die-cast aluminum is especially popular in gear cases for cool running and holding the gear train in a precise location. A glass-filled nylon housing offers better impact resistance than aluminum.
Double-insulated plastic is a nonconductor and has lower heat retention. Some power units, while not double insulated, feature plastic-coated handles for this reason.
Housing should have adequate ventilation and exhaust ports.
If the electrical unit does short out, the operator is protected from shock by a double-insulated housing. As a result, double-insulated tools do not require three-wire grounding cords.
In a single-insulated tool, the motor windings are insulated from the housing and a three-wire cord is used to ground the housing in the event a short does occur. The tool should be plugged into a socket with a ground. If an extension cord is used, it also should be a three-wire grounded cord.
There are more than 150 variations of motors that drive power tools. Among the quality features are welded connections, built-in fans and commutators welded to motor windings.
Bearings can be oil-impregnated brass or steel ball, needle or roller bearings, with ball and needle bearings in higher-quality motors.
A higher horsepower usually means more power or torque at a given speed as well as less wear on the motor under prolonged use. Power tools such as drills, saws, etc., will have a range of horsepower ratings with minimal horsepower for the occasional do-it-yourselfer through maximum power for commercial uses.
Switches used on power tools are “on-off”, multi-speed and variable speed. On drills, a reversing switch is frequently used.
A toggle switch merely turns the unit on or off, providing only one operating speed. Trigger switches are usually designed to spring to the off position when finger pressure is released.
Multi-speed switches allow the user to select two or more speeds. The switch usually must be manually moved to the off position to stop the motor.
Variable speed switches allow speed settings at any level from minimum to maximum by varying the pressure on the power trigger. This allows slow starting for situations such as starting a hole in metal with a drill. Some units are provided with a switch lock to set speed for continuous operation at a specific level.
Some premium-grade tools, both corded and cordless, are using variable speed switches with electronic feedback that will keep the tool working at the speed desired under load.
Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the North American Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.