Drilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross-section in solid materials. The drill bit is a rotary cutting tool, often multipoint. The bit is pressed against the work piece and rotated at rates from hundreds to thousands of revolutions per minute. This forces the cutting edge against the work piece, cutting off chips (swarf) from the hole as it is drilled.
Technical bit: Under normal usage, swarf is carried up and away from the tip of the drill bit by the fluting of the drill bit. The cutting edges produce more chips which continue the movement of the chips outwards from the hole. This is successful until the chips pack too tightly, either because of deeper than normal holes or insufficient backing off (removing the drill slightly or totally from the hole while drilling). Cutting fluid is sometimes used to ease this problem and to prolong the tool’s life by cooling and lubricating the tip and chip flow. When cutting aluminium in particular, cutting fluid helps ensure a smooth and accurate hole while preventing the metal from grabbing the drill bit in the process of drilling the hole. Different drill bits are used to drill metal depending upon hardness, thermal properties of the metal and hole diameter required. The drill speed is also adjusted depending upon the thermal properties and hardness of metal. For example, when cutting stainless steel slower speed is recommended than steel. Drilling too fast on stainless steel will heat it up easily and make it hard quickly which makes it very difficult to drill.