drill

A drill is a tool with a rotating drill bit used for drilling holes in various materials. Drills are commonly used in woodworking and metalworking.

The drill bit is gripped by a chuck at one end of the drill, and is pressed against the target material and rotated. The tip of the drill bit does the work of cutting into the target material, slicing off thin shavings (twist drills or auger bits) or grinding off small particles (oil drilling).

History

The earliest drills were probably bow drills. The invention of the electrical drill is credited to both Arthur James Arnot [1], in 1889, at Melbourne, Australia and Wilhelm Fein [2], in 1895, at Stuttgart, Germany. In 1917, Black & Decker patented a trigger-like switch mounted on the handle.

Types

There are many types of drills; some powered by hand and others using electricity or compressed air as the motive power. Drills with a percussive action (such as hammer drills, jackhammers or pneumatic drills) are usually used in hard materials such as masonry or rock. As well, drilling rigs are used to bore holes in the earth to obtain water or oil. An oil well, water well, or holes for geothermal heating are created with large drill rigs up to a hundred feet high. Some types of hand-held drills are also used to drive screws.

Hand tools

A variety of hand-powered drills have been employed over the centuries. Here are a few, starting with approximately the oldest:

• Bow drill
• Brace and bit
• Gimlet
• Breast drill, also known as "eggbeater" drill
• Push drill, a tool using a spiral ratchet mechanism
• Pin chuck, a small hand-held jewellers drill

Electric Drill

Hand-held electric drills are ubiquitous. They usually look like a pistol, with a trigger-like switch. They are also used for driving screws and are often provided with a hammer action which makes them capable of being used as masonry drills. In fact, screw guns or electric screwdrivers are generally suitably modified drills.

These drills typically employ a universal motor with brushes. The original designs featured a single forward speed with a simple on-off action of the trigger; they could operate equally well on AC or DC power. Modern variable speed drills contain solid state phase control circuits that limit their use to AC power only. As a tradeoff, the electronics now give them variable speed, reversibility and torque control.

Hammer Drill

The hammer drill is similar to a standard electric drill, with the exception that it is provided with a hammer action for drilling masonry. The hammer action may be engaged or disengaged as required.

Rotary hammer drill

The rotary hammer drill (also known as roto hammer drill or masonry drill) is an electric drill type dedicated to drilling holes in masonry. The rotary hammer drill is a percussion drill that uses a weight to create the impact force on the masonry bit. Generally, the drill chuck of the rotary hammer drill is designed to hold SDS drill bits. Some styles of this drill are intended for masonry drilling only and the hammer action cannot be disengaged. Other styles allow the drill to be used without the hammer action for normal drilling.

Cordless drills

A cordless drill is a type of electric drill which uses rechargeable batteries. These drills are available with similar features to an AC mains-powered drill. They are available in the hammer drill configuration and most also have a clutch setting which allows them to be used for driving screws.

For continuous use, a tradesman will have one or more spare battery packs charging while working, so that he can quickly swap them, instead of having to wait several hours during recharges.

Early cordless drills started with interchangeable 7.5V battery packs, and over the years the battery voltage has been increased to 18V, and higher, allowing these tools to produce as much torque as many mains-powered drills. The drawback of most current models is the use of nickel-cadmium (NiCd) batteries, which develop a "memory effect" or internal short circuits due to dendrite growth, severely limiting their useful life, and posing a hazardous materials disposal problem. Drill manufacturers are now introducing lithium ion batteries, most notably Makita Electric Works and Milwaukee Electric Tool Corporation. The main advantages are lack of memory effect and very short charging time. Instead of charging a tool for an hour to get 20 minutes of use, 20 minutes of charge can run the tool for an hour. Lithium ion batteries also have a constant discharge rate. The power output remains constant until the battery is depleted, something that nickel-cadmium batteries also lack, and which makes the tool much more versatile. Lithium-ion batteries also hold a charge for a significantly longer time than nickel-cadmium batteries, about 2 years if not used, vs. around 4 months for a nickel-cadmium battery.

Drill press

A drill press (also known as pedestal drill, pillar drill or bench drill) is a fixed style of drill, which may be mounted on a stand or bolted to the floor or workbench. It consists of a base, column (or pillar), table, spindle (or quill) and drill head, usually driven by an induction motor. The head has a set of handles (usually 3) radiating from a central hub which, when turned, move the spindle (and chuck) vertically, parallel to the axis of the column. The table can be adjusted vertically and is generally moved by a rack and pinion, however some older models rely on the operator to lift and reclamp it in position. The table may also be off-set from the spindle's axis and in some cases rotated perpendicular to the column.

A drill press has a number of advantages over a hand held drill:

• less effort is required to apply the drill to the workpiece. The movement of the chuck and spindle is by a lever working on a rack and pinion, this gives the operator considerable mechanical advantage.
• the table allows a vise or clamp to position and lock the work in place making the operation secure.
• the angle of the spindle is fixed in relation to the table allowing holes to be drilled accurately and repetitively.

Speed change is achieved by manually moving a belt across a stepped pulley arrangement, some types introduce a third stepped pulley to increase the speed range. This makes selecting the correct spindle speed more likely.

Geared head drill

The geared head drill is identical to the drill press in most respects, however they are generally of sturdier construction and often have power feed installed on the quill mechanism, and safety interlocks to disengage the feed on overtravel. The most important difference is the drive mechanism between motor and quill is through a gear train (there are no vee belts to tension) this makes these drills suitable for the larger sizes of drill bits (16 mm or 5/8ths" upwards) which would normally stall in a drill press.

Radial arm drill

A radial arm drill is a geared head drill that can be moved away from its column along an arm that is radiates from the column. These drills are used for larger work where a geared head drill would be limited by its reach, the arm can swivel around the column so that any point on the surface of the table can be reached without moving the work piece. The size of work that these drills can handle is considerable as the arm can swivel out of the tables area allowing an overhead crane to place the workpiece on the fixed table. Vices may be used with these machines but the work is generally bolted to the table or a fixture

Mill drill

Mill drills are a lighter alternative to a milling machine, they combine a drill press (belt driven) with the x y co-ordinate abilities of the milling machines table and a locking collet that ensures that the cutting tool will not fall from the spindle when lateral forces are experienced against the bit. Although they are light in construction they have the advantage of space saving combined with versatility and are suitable for light machining which may otherwise not be affordable.

Related tools

• Milling machines, metal lathes and routers are also used for drilling.

See also

• auger
• well drilling
• oil drilling
• hammer drill
• bow drill
• drill bit
• Boring (mechanical)
• Core drill

External links

• air drill or pneumatic drill
• How to choose and buy a cordless drill - what should you look for.