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Most DIY enthusiasts, handymen and builders in London will have a case full of different drill bits to cope with different drilling tasks. Wood drill bits, metal drill bits and masonry drill bits are the three most common, and inasmuch as many people appreciate that the drill bits are manufactured for specific tasks, not a lot of people know why drill bits are designed the way they are and how best to use them.
Drilling Wood
Almost any drill bit can be used for drilling a hole in a soft wood, but the “lip and spur” drill bit is best to use. It has a centring point which keeps the drill bit steady against the wood (the “spur”) whilst the raised corners of the drill bit cut through fibres within the grain of the wood cleanly – before the inner parts of the cutting edges plane off the base of the hole. Also ideal for drilling through soft plastics, the “lip and spur” is usually used in sizes from 3mm (1/8th inch) to 16mm (5/8th inch).
For wider holes, spade or paddle bits are recommended. These are flat-headed drill bits with a centring point and two cutters which are equipped with spurs to enable a cleaner cutting edge.
Augur wood drill bits are made with a spur, single cutting edge and a “flute” for removing waste from the drilled hole and are particularly useful for drilling deep holes in wooden surfaces.
Drilling Metal
There are many different types of drill bits for drilling through metal, and your choice of bit should depend on the type of metal you are drilling through (steel, stainless steel or aluminium for example) and the size of hole that you wish to make. The larger the hole, the more friction will be created and the hotter the drill bit will become leading to overheating and damage to the drill bit. Most power drill handbooks provided recommended drilling speeds for drilling through metal and you can also refer to Mr Skill´s Project Advice article on “How to Drill Through Metal” and our “Drill Speed Chart”.
The cheaper metal drill bits are made from high carbon steel, but lose their cutting edge quickly if allowed to overheat. Therefore, most builders in London have a preference for “high speed steel” which can be used to drill through metal, hardwood and most other materials at higher speeds. Although being more brittle than “high speed steel”, drill bits made from cobalt steel alloys hold their hardness at much higher temperatures, whilst tungsten carbide drill bits are the toughest of the lot. Due to its expense, tungsten carbide – and polycrystalline diamond (PCD) – is most commonly used on the tips of metal cutting drill bits.
Coatings are frequently used on metal cutting drill bits to provide heat resistance and increase lubricity. The most common are black oxide and titanium nitrate, which can extend the life of a drill bit three or four times, although the benefits or titanium aluminium nitride and titanium carbon nitride are worth the expense if you do a lot of drilling through metals such as stainless steel and nickel alloys.
Drilling Masonry
Masonry bits are usually used with a hammer drill by builders in London. The bit is both hammered and rotated into the masonry – the hammering breaks up the masonry at the drill bit tip, whilst the rotating flutes of the drill bit body carry away the dust. Rotating the bit brings the cutting edges in contact with a fresh portion of the hole with every hammer blow.
Masonry bits of the style shown are commonly available in diameters from 5mm (¼ inch) to 40mm (1½ inches). For larger diameters, core bits are used. Masonry bits up to 1000mm (39 inches) long can be used with hand-portable power tools, and are very effective for installing wiring and plumbing.
This is only a selection of the most common drill bits used in home improvement. If you require any further information on specialist drilling tools, please consult one of the highly rated builders in London featured in our Tradesmen´s Directory.