Choosing A Drill
by Derick Martin
Because of its versatility, the electric drill is a wise choice for the homeowner's first portable power tool. It can drill metal, wood, plastic, and concrete, and perform many other operations as well. The size of the drill is determined by the largest drill shank its chuck will accept, which may be 1/4, 3/i, 1/2, or 3/4 inch. The 1/4-inch size is handiest for the average home workshop. A drill's power varies with size and make but typically ranges from about IA hp in the 1/4-inch size to as much as 11/2 hp in 3/4-inch models.
Speed usually decreases with size (though turning power increases), ranging from about 2000 rpm for 1/4-inch size to around 1200 rpm for 3/8'inch and 600 rpm for 1/2-inch drills. The 3/4-inch size (largely for professional and industrial use) is commonly in the 250-475 rpm range. The slower speeds of the larger drills provide greater turning power ( torque) necessary for driving large diameter bits and hole saws. The high speed of the 1/4-inch drills equips them not only to drill holes up to 1/4-inch diameter in metal and 1/2 inch in wood, but also for sanding.
Variable speed control is also available on many 1/4- to 1/2-inch models; some 3A- and 1/2-inch drills are also reversible. The speed control lets you select the best drilling speed. Reverse is useful in backing out wood bits from deep holes. Heavy-duty drills of any given size vary more widely in price than do the light-duty models because of differences in bearings, wiring, and other features. For normal home use, heavy-duty features are not usually necessary. Most drills are equipped with 3-wire grounding cords (with 3-prong plugs) to protect the user from shock in case of internal electrical damage. If you buy a drill with a 2-prong plug, be sure the tool is a type in which the outer shell and chuck are completely insulated from the wiring. Such drills are commonly termed double-insulated drills.
Many drills come with a polyethylene plastic'carrying case which generally also contains an assortment of accessories. Whatever drill you buy, check the guarantee as well as the availability of parts. Your best guide to quality is a reputable manufacturer.