From DIYinfo.org
[edit] The Right Bit For The Right Job!
Drilling holes in things is the mainstay of every do-it-yourselfer's workload, and to get good results you need to have a selection of the right drill bits for every job in your toolkit.
By far the biggest range of drill bits available are for drilling holes in wood and metal.
Twist drills
Are the commonest and most widely used, for drilling small holes in wood and metal up to about 32 mm in diameter. Most are now produced in metric sizes, but imperial sizes are still available. Twist drills are made from either high-speed steel (HSS), which is tough but fairly expensive, or carbon steel which is cheaper but doesn't wear so well.
Wood bits
Are similar in appearance to twist drills, but have a central point which helps to locate the bit more accurately when starting drilling. They are available in larger diameters up to 20 mm; larger sizes have reduced shanks to fit standard 13 mm drill chucks. Both twist drills and wood bits can be used in power or hand drills.
Auger bits
Have a deep-cut spiral shaft with a wide cutting edge and a tapered point for accurate positioning, and are used to drill large, deep holes accurately in sizes up to about 35 mm across. They're used with a carpenter's brace.
Flat bits
Sometimes called spade bits, have a different shape to other bits. Instead of a round spiralled shank, there is a single spade-like cutter which can be up to about 35 mm across. They're designed for use only with power drills.
Expansive bits
Resemble spade bits, but have a movable outer cutter and can make holes up to around 75 mm in diameter. They're designed for use in hand drills and braces, and are expensive.
Hole saws
Offer a cheaper way of cutting large holes in wood up to about 30 mm thick. They consist of an arbor containing a twist drill and carrying a circular blade. The drill locates the hole centre and then draws the blade down into the wood. Various sizes are avail-able, up to a maximum diameter of 150 mm. Nests of saws include several interchangeable blade sizes.
Countersink bits
Are used to form a neat conical recess in the wood surface, so allowing a countersunk screw head to lie flush.
Screw sinks
Are a combined, miniature flat bit and countersink bit, designed to drill pilot, clearance and countersink holes in one operation.
You can use high-speed steel twist drills for drilling metal too, and a hole saw with a special blade can cut holes in thin metal sheet. Alternatively, a tank cutter with its adjustable cutting blade can be used instead, fitted to a brace.
[edit] For Drilling Masonry
You need special masonry drills which have tungsten carbide cutting tips brazed onto the end of the drill shaft.
Masonry drills may be sized in millimetres, or according to the gauge number of the screw that will fit the hole.
Most are a standard length, but extra-long types are available for drilling holes right through walls to take things like pipes or electric cables.
Special high-impact types are required for use with power drills featuring hammer action.
Core drills are used for making larger holes than an ordinary masonry drill can manage.
[edit] For Drilling Glass and Tiles
For drilling glass and mirrors you need a special spear-point drill, used with plenty of lubrication.
As for drilling tiles you can use a masonry bit.
Note it is a good idea to put some kind of tape on the tile first before drilling, as this will prevent chipping of the tile surface.
[edit] Sharpen Twist Drills
To sharpen twist drills, use a sharpening attachment with a power drill, or else a special jig (right) with a grinding wheel.
Both these items are readily available in most hardware stores.
