Boring

Boring, a process of cutting holes in wood, metal, rock, or other material, by means of special tools designed for the purpose. For small holes in soft material the tool merely forces its way into the substance, but generally the borer is a rotating piece with a cutting edge. Thus for hard wood we have the gimlet, a cylindrical screw tapering to a point at one end, and having its threads cut in such a way as to peel off little shavings as the tool penetrates the material. Of this type of cutter there are several varieties. The brace and bit dispenses with the cylindrical screw, consisting only of the cutting edge at the end. It may be employed for cutting very large holes in wood. Similar to the brace and bit is the ordinary boring machine used for iron and other heavy metal work. Requiring more power, the framework of the machine must be substantial and must have firm foundations. It is usually driven by steam. The drill is modified at its cutting edge to suit the hard material it has to cut; the metal comes away in small, thin chips. The speed of rotation must not exceed a certain definite limit, fixed for each type of metal, and much slower than that for wood. If this is exceeded the metal is torn away irregularly, and the tool is in danger of losing its temper and breaking. The work is fixed to a table that admits of adjustment in various positions relative to the tool, the feeding of which may be done mechanically or by hand. The borer does not always cut out the entire hole. Sometimes the hole is already cast or wrought, and only requires uniform cutting to the requisite dimensions, as in the case of steam-engine cylinders. For this work special cutters are arranged on to a cylindrical bar, which may be fixed while the steam cylinder or other piece of work may be made to rotate. A solid core may be cut out entire by aid of a trepanning bar - a hollow cylinder with cutters round the front edge. For rock-boring diamond drills are most generally used. The cutting edges are supplied by black diamonds, or carbonados, fixed round the front edge of a hollow steel cylinder, as are the cutters in the trepanning bar. Lengths of iron tubing are screwed on to this as the crown is made to penetrate deeper and deeper into the soil. The nature of the cores of earth contained in the hollow rods shows exactly the disposition of the strata penetrated. The detritus is washed away by a current of water. Boring-rods act on the principle of augers, but are not so efficient as diamond drills. Nor are rope-borers so efficient, long used by the Chinese, and effective when the rocks are soft, In this case the cutter is attached to a rope, and descends by force of gravity, thus forcing its way through the earth. The detritus is lifted up by a scoop.