Post –by Gautam Shah
Drilling is a very old craft practised by various civilizations. Historically materials like shell, ivory, antler, bones, tooth and baked ceramics, have been pierced through to make adornments. Means and methods for drilling of hard materials like stones, glasses, metals, nodules and beads were developed by ancient people. Soft materials like skins (hides, leather) were punched for stitching or tying.
Deep-set teeth like wisdom (third molar) of live patients were drilled during 7000 and 5500 BC. Skulls with signs of trepanation have been found in prehistoric human remains from Neolithic times onward. Trepanning, (trephination, trephining) or making a burr hole is probably the oldest surgical procedure, dating 40,000 years. It is a surgical intervention in which a hole is drilled or scraped into the human skull to cure epileptic seizures, migraines, and mental disorders. It was also done to remove shattered bits of bone from a fractured skull and clean out the blood that often pools under the skull after a head injury.
Drills have been used for producing new holes, enlarging existing holes and also for shaping cavities to various forms of sections. Drills with special attachments are also used for creating threads inside cylindrical forms. Shallow depth drilling has been used for etching, engraving and carving on very hard surfaces like obsidian and for material removing and surface polishing.
About 110,000 years back Neanderthal man began to use many different types of handled tools like axes, borers, knives and spears. In all these tools, the edges were heavily notched (due to chipping of the stone) but a toothed edge helped in carving, cutting and boring processes for materials like horn, bone, skins, wood, stones, etc. Wood, natural fibres and bones complimented the edge stones for handling and gripping. Approximately 35 000 years back, Cro-Magnon man devised newer tools. Burin, an engraving tool, was made from a sharp narrow flint blade, for incising and burrowing. This made it possible to work the horn and bone into combs, needles, beads and such other small items. Tools similar to a burin were used for cleaning and shaving hides.
Flint blades slimmed to a sharp point were used for piercing holes. Another method could have been to grind a hole with abrasive sand under the point of a stick. Diamond points (‘jeweled’) were used as drilling bits.
The Egyptians invented the circular trephine, made by of a tube with serrated borders (similar to the country tool used for punching a large size hole in masonry structure). It gives a round disk like cut called ‘crown’. The crown cut was worn by the patient to ward off evil.
An awl and the needle were the first hole making tools. These create a hole by shifting or compressing the material to sides rather than removing it. Small, shallow holes in stone, concrete, brick, and similar materials are usually drilled by a hand star punch, (a steel rod with an X-shaped cutting point, which was held against the object to be holed and struck with a hammer or sledge while revolving slightly after each stroke). A hardened metal punch is used even today to push a hole in fragile materials like plaster, bricks. Paper leather, etc. Punch is also used to mark a small indentation, so that drilling bit has a homing mark. Metal sheets cannot be drilled properly so are holed by a pointed punch or a punching die.
The bow drill is an ancient form of drilling tools. It was commonly used to make fire, and was also called a fire drill. However, the same principle also was used widely in drilling for wood and teeth. Bow drills were used since 4th C. BC to drill holes into lapis lazuli and cornelian.
Augers are large size hole making tools. Initially in the Iron Age it was a simple cutting bar or plate joined at a right angle to an axle which could be rotated. Later it was like a short length split pipe. The auger was used for boring softer materials. It removed large quantity of material due to its wide size capacity, so had to be taken out to remove the cut material. Middle age Augers with spiral or helical flutes helped the evacuation of the cut material to the surface. Augurs are now used for pile foundation boring work, tree planting etc.
Chinese, 2,250 years ago, used Augur based drilling device to drill shallow wells to tap brine aquifers for salt production. The rig was constructed from bamboos. The pile pipe with drill bit was allowed to drop by about one mt pulverizing the rock. By the beginning of the 3rd C. AD. wells were drilled up to 140 mts depth. In 1835 the Shanghai well was the first in the world to exceed a depth of 1000 mts in comparison, the deepest wells in the USA were about 500 mts deep.
The other hand boring tools include the brace, a crank shaped device that can be held by one hand and rotated by another (action similar to car lifting jack), the push drill has a spiral flute along which a trunk moves down creating rotations but bounces back, on release of the compressed spring.
The rotary hammer drill (masonry drill) combines a primary dedicated hammer mechanism with a separate rotation mechanism, and is used for more substantial material such as masonry or concrete.
Table or platform drills are used in workshops for cutting holes in wood, metal, rock, or other hard materials. Table mounting is required where jobs are heavy, repetitive and precise. Platform mounting is used for simultaneous or multi drill operations. Tools for drilling holes in wood are commonly known as bits. A number of special forms of bits are also employed, including the expanding bit, which has a central guide screw and a radial cutting arm that can be adjusted to widen already drilled holes. For drilling metal, twist drills rotated by motor-drives are employed.
Chucks are holding devices to drills of various sizes. Rock drills are hammered by pneumatic devices for creating holes to place explosive charges in mining and quarrying. A rotary drill consists of a single auger-like bit, or three inclined positioned circular sets of multiple bits moved by a toothed gear, and the gear rotated by a series of connected steel pipes. Rotary drills are used in drilling oil wells.
Drilling and Boring Machines: Motorized drill machines not only drill new holes, and alter the existing holes by boring or reaming to enlarge it, cut screw threads by tapping it, or lap or hone a hole for accurate sizing (tolerances) and to provide a smooth finish. Drilling machines vary in size and function, ranging from portable to very large radial drilling machines, multi-spindle units, automats or automatic production machines, and deep-hole-drilling machines.
Routers are machines with drilling spindles that move sideways to cut shallow to deep grooves with square or rounded sections to create engraved patterns in materials like wood, plastics and metals. Drilling machines are also operated with pressurized gas -pneumatically, to achieve very high speeds.
Common drills have a single cutting tip of steel made of hardened, carbon steel or tipped with cemented carbide or diamond. A carpenter’s hand held wooden drill takes forward and backward motion from the thong or bow-thread. The dual movement helps in drilling as well as evacuation of dust. Dual movement require double edged drilling bit, compared to a single direction movement bit, which are easy to make and re-sharpen. Drilling bits with spirally fluted columns came into practice much later, in 19th C.
Drilling is done with a small diameter-axial movement so requires high speed and low torque. Drilling removes very little material per rotation. Boring is done with a large diameter so requires low speed but high torque. For finishing large bores grinding wheels are used. Grinding-wheel cutters have a planetary motion, rotating rapidly on their own axes, which in turn rotates on the internal face of the bore.