Drill ratings are based on chuck capacity and motor load limit.
Chuck capacity is the most obvious, but it does not tell the whole story. Speed and torque, or twisting power, must be considered.
For example, a drill rated at 1/4″ not only means that this is the largest-diameter shank that will fit the chuck but indicates the largest-sized hole recommended to be drilled with a 1/4″ bit in 1/4″ thick mild steel. The peripheral speed of the drill bit increases with the size; therefore the bit determines the rated drill capacity.
Motor load limit is classified light, medium or heavy duty. Amp ratings and bearing construction are a better method for determining which classification a drill falls into than its chuck size.
Horsepower ratings are determined individually for each tool according to its use, amperage, torque and type of bearing. Ratings vary by manufacturer. General ranges include 1/7 to 1/4 hp for 1/4″ and 3/8″ drills, 1/3 to 7/8 hp for 1/2″ units.
Rating listed on drill nameplate usually includes amperage. The higher the amp rating the more powerful the drill. Drills rated at two amps are generally considered light-duty units, while five-amp units are for heavy-duty work.
A good quality 1/4″ drill has sufficient power to drill holes in concrete, metal, plastic and other materials. Accessories and attachments make it an excellent tool for shop and home.
Quality features include geared key chuck, aluminum or heavy-duty plastic housing and heavy-duty reinforced cord. Helical gears are not needed on 1/4″ drills since they are not high-torque tools like 1/2″ drills or circular saws.
Heavy-duty 1/4″ drills handle tougher jobs. Bearings are heavier. They are higher priced than regular 1/4″ drills.
In addition to extra chuck capacity, 3/8″ drills are normally built with double-reduction gear systems to provide more torque and to operate at lower speeds, generally about one-half the rpm of a 1/4″ drill. The slower speed eases starting holes in slick surfaces and reduces drill bit burn-out when drilling with larger-diameter bits in steel. Usually priced between regular and heavy-duty 1/4″ drills.
Three-eighths-inch drills usually handle more attachments than 1/4″ and can perform most of the jobs a 1/4″ does-sanding and buffing are about the only jobs needing a 1/4″ drill’s higher speed.
Heavy-duty 3/8″ drills with reversing action and screwdriver attachments are also available.
Keyless chucks are becoming more common on 3/8″ and 1/2″ drills.
Generally used by tradesmen, the high torque and slow speeds of 1/2″ drills make large holes in wood or metal. These drills-because of their slow speed-provide good power units for hole saws.
In drilling large holes in wood beams, self-feeding bits are frequently used to reduce force required by the operator. Reversing action permits jammed drill bits to be backed out easily from wood or masonry.
VARIABLE SPEED DRILLS
Variable speeds offer many advantages in drill design, the most important of which is the ease with which a hole can be started in masonry, ceramics and in steels particularly where curved or compound surfaces (such as drilling a piece of pipe) are encountered. However, an electronic speed reduction does not increase drilling torque or power.
Variable-speed drills offer speed or torque control from zero to maximum revolutions per minute. Usually, variance is achieved by varying pressure on the trigger switch. There are some tools, however, where speed is set by dial control.
Most 1/4″ drills operate between 1,600 and 2,800 rpm; speeds for 3/8″ units range from 650 to 1,350 rpm, and those of the 1/2″ model are around 500 rpm. Depending on such factors as load, drill size and material, speed drops from 30 percent to 50 percent in use.
Many portable drills feature reversing action-greatly increasing their versatility.
This allows the operator to drive and remove screws, nuts and bolts, drill and tap threads in metal and o other jobs not possible with conventional drills. The chuck is locked in place so it will not spin off when using the reverse action.
Some drills also allow the operator to select desired speed or rpm by turning a small adjusting knob built into the trigger or switch. This makes it possible to maintain a pre-selected speed as required for specific applications, such as slow speed for drilling in stainless steel or glass.
Hammer-drills cut into concrete, stone, block and brick quickly and easily. Hammers with the dual function of slow drilling are doubly useful to the handyman in that they will drill and ream wood, steel, etc.
Hammer-drills have a conventionally geared chuck. The vibrating action speeds the drilling in most concrete or masonry products when equipped with a carbide-tipped drill bit. Most models have a “model” selector allowing the operator to choose rotation only, as in a conventional drill, or “hammer-drill” coupling the vibrating action with the rotary motion. Some models offer a third choice of hammer only, which in some cases can accommodate chisel and scraper attachments.
A hammer-drill should not be confused with the rotary-hammer professional tool which has drilling capacities of 1/4″ up to core bits of 6″ diameter. These larger hammers have unique bit drive and retention methods rather than the conventional geared chuck.
Depending on the manufacturer, hammer-drills range from very low speeds for controlled, fine drilling and impacting to high-speed drilling and hammering for fast, productive work. Some have variable speed controls. Chuck sizes range from 1/4″ to 1/2″.
Impact wrenches, long used in commercial applications, have applications in the home and on the farm. These tools are normally used only occasionally by do-it-yourselfers.
Electrically powered, the wrenches deliver 2,000 impacts per minute utilizing a socket wrench attached to the drive shaft. Quality is critical since the wrench must have enough power to loosen tight bolts and the motor must be protected against burnout.
Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the National 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.