The process of boring holes may be viewed as an inversion of that of turning; generally the work remains at rest, and the tool is revolved and advanced. Many of the boring and drilling tools have angular points, which serve alike for the removal of the material, and the guidance of the instrument; others have blunt guides of various kinds for directing them, whilst the cutting is performed by the end of the tool.

Commencing as usual with the tools for wood, the brad-awl fig. 450, may be noticed as the most simple of its kind; it is a cylindrical wire with a chisel edge, which rather displaces than removes the material; it is sometimes sharpened with three facets as a triangular prism. The awl, fig. 451, used by the wire-workers, is less disposed to split the wood; it is square and sharp on all four edges, and tapers off very gradually until near the point, where the sides meet rather more abruptly.

The generality of the boring instruments used in carpentry are tinted, like reeds split in two parts, to give room for the shavings, and they are sharpened in various ways as shown by figures 452 to 456. Fig. 452 is known as the shell, and also as the gouge-bit, or quill-bit, it is sharpened at the end like a gouge, and when revolved it shears the fibres around the margin of the hole, and removes the wood almost as a solid core. The shell-bits are in very general use, and when made very small, they are used for boring the holes in some brushes.

Fig. 453, the spoon-bit, is generally bent up at the end to make a taper point, terminating on the diametrical line; it acts something after the manner of a common point drill, except that it possesses the keen edge suitable for wood. The spoon-bit is in very common use, the coopers' dowel-bit, and the table-bit, for making die holes for the wooden joints of tables, are of this kind; occasionally the end is bent in a semicircular form, such are called duck-nose-bits from the resemblance, and also brush-bits from their use; the diameter of the hole continues undiminished for a greater depth than with the pointed spoon-bit.

Boring Tools Section I Boring Bits For Wood 20057

The nose-bit, fig. 454, called also the slit-nose-bit, and auger-bit, is slit up a small distance near the center, and the larger piece of the end is then bent up nearly at right angles to the shaft, so as to act like a paring chisel; and the corner of the reed, near the nose also cuts slightly. The form of the nose-bit, which is very nearly a diminutive of the shell-auger, fig. 455, is better seen in the latter instrument, in which the transverse cutter lies still more nearly at right angles, and is distinctly curved on the edge instead of radial. The augers are sometimes made three inches diameter, and upwards, and with long removable shanks, for the purpose of boring wooden pump-barrels, they are then called pump-bits.

There is some little uncertainty of the nose-bits entering exactly at any required spot, unless a small commencement is previously made with another instrument, as a spoon-bit, a gouge, a brad-awl, a center-punch or some other tool; with augers a preparatory hole is invariably made, either with a gouge, or with a center-bit exactly of the size of the auger. When the nose-bits are used for making the holes in sash bars, for the wooden pins or dowels, the bit is made exactly parallel, and it has a square brass socket which fits the bit; so that the work and socket being fixed in their respective situations, the am de-principle is perfectly applied. A "guide tube" built up as a tripod which the workman steadies with his foot, has been recently applied by Mr. Charles May, of Ipswich, for boring the anger holes in railway sleepers exactly perpcmlienlar.* The gimlet fig, 456 is also a fluted tool, hut it terminates in a sharp worm or screw .beginning as a point and extending to the full diameter of the tool, which is drawn by the screw into the wood. The principal part of the cutting is done by the angular cornerr intermediate between the worm and shell, which acts much like the Niger, the gimlet is worked until the shell is full of wood, when it is unwound and withdrawn to empty it.

The center-bit, fig. 457, shown in three views, is a very beautiful instrument, it consists of three parts, a center point or pin, tiled triangularly, which serves as a guide for position; a thin shearing point or nicker, that cuts through the fibres like the point of a knife; and a broad chisel edge or culler, placed obliquely to pare up the wood within the circle marked out by the point. The cutter should have both a little less radius and less length than the nicker, upon the keen edge of which last the correct action of the tool principally depends.

Many variations are made from the ordinary center-bit, fig. 457; sometimes the center-point is enlarged into a stout cylindrical plug, so that it may exactly till a hole previously made, and cut out a cylindrical countersink around the same, as for the head of a screw bolt. This tool, known as the plug center-hit, is much used in making frames and furniture, held together by screw-bolts. Similar tools but with loose cutters inserted in a diametrical mor- tise, in a stout shaft, an also used in ship-building for inlaying the heads of bolts and washers, in the timbers and planting.

The wine-cooper's center-bit is very short, and is enlarged behind into a cone, so that immediately a full cask has been bored, the cone plugs up the hole until the tap is inserted. The center-bit deprived of its chisel-edge, or possessing only the pin and nicker, is called:a button-tool, it is used for boring and cutting out at one process, the little leather disks or buttons, which serve as nuts for the screwed wires in the mechanism connected with the keys of the organ and piano-forte.

Boring Tools Section I Boring Bits For Wood 20058

• See Minutes of Conversation Inst. Civil Engineers. 1842, page 76.