The internal cylinder in hardwood and ivory turning, comprises all parallel apertures, commencing with the fine holes required for the insertion of pins or analogous purposes, which are made by drilling; followed by larger apertures, from about one eighth of an inch to about one and a half inches in diameter, which when comparatively shallow are produced with the turning tool, and when deep, also by boring; to those large openings often produced by the turning tool alone, but as frequently, commenced by boring and completed by turning.

Fine drilled holes of moderate depth, are conveniently bored with a drill made of a piece of round steel wire inserted in a handle. The end of the wire is flattened and slightly spread with the hammer, and then ground flat on the two sides, the cutting end is formed and sharpened with two bevils, meeting in a central point, the form of fig. 476, Vol. II. In common with other pointed drills, this requires a conical hollow center, to be made for its first entry in the work, fig. 357, which center is usually turned with a point tool. The pointed drill, as previously explained, does not keep a true line in boring deep holes; for these, the round steel wire is ground or filed away on one side down to the diametrical line, and sharpened nearly square across the end, forming the cutting edge as in the cylinder bit. This drill called a pipe bit, is used for holes from about one sixteenth, to one eighth of an inch in diameter, and from about six to twelve inches deep respectively. A conical center, just large enough to embrace its diameter, is made for the first entry of the pipe bit, and, on account of its flexible nature, the bit is at first pressed into the work held by-its shaft near the cutting end, supported between the thumbs and two first fingers of both hands. The handle is not grasped until the tool has bored to the depth of three or four inches, and then, the left hand continues to support the blade during its advance into the work. Both of these wire drills require frequent withdrawal from the work to clear them from the shavings, which, collecting upon their sides and ends as a hard substance, impede their cutting.

Internal cylinders, to about one and a half inches diameter, exceeding two or three times their diameter in depth, may be conveniently made by drilling. The twist drill, has a nearly parallel round shaft, with two spiral flutes opposite to each other along its entire length; the flutes form two cutting edges with two bevils, ground across the end of the drill, meeting in a central line, and the opposite end of the drill is provided with a hollow center. The twist drills may be used in a chuck, in a handle, or advanced by the point of the popit head, and are made to definite measures. The smaller sizes, to about a quarter of an inch diameter, may generally be used upon the solid material; holes of larger diameter, are gradually enlarged by several bits used in succession. The twist drill cuts after the same manner as the pointed drill, fig. 476, Vol. II., but more nearly true. The shaft nearly fills the hole by the cylindrical surfaces separating the flutes, so that the tool has considerably less tendency to escape sideways, and the hole, which is left pointed at the bottom, fig. 355, is much less liable to be bored inaccurately. The fluted drill, has two opposite straight flutes, parallel with its length, in other respects it is ground, used, and cuts, in the same manner as the twist drill.

The cylinder bit, called also the half round bit, fig. 507, Vol. II., bores a smooth, perfectly true hole, flat at the bottom; the bits are made to definite measures and range from about one eighth, to one and a half inches in diameter, and are from about four, to fifteen inches in length, respectively. The cutting end is first turned as a short cylinder, and then filed down to the diametrical line, leaving the section exactly, or not less than the half circle; the half cylinder entirely prevents any lateral escape of the tool from the axial line, and also gives free egress to the shavings. The cutting edge is the angle formed by the diametrical face with the end of the tool; the end is ground nearly square across and nearly vertical, both to give the cutting angle, and to cause the line of the edge on the right hand side of the center, which does no cutting, to stand slightly behind the left hand or cutting half. The flat shaft of the bit has a hollow center at the opposite end for the point of the popit head, and the smaller sizes below half an inch, are convenient when mounted in wooden handles, which should be provided with metal hollow centers at their butt ends. The cylinder bits and others, are prevented revolving with the work by a hand vice or hooked wrench, temporarily fixed to their shafts, and held in the hand or allowed to lie on the rest; the smaller sizes have their handles grasped by the hand or a small lever is placed through a transverse hole in the handle, with the same object. They all require occasional withdrawal from the hole in process of boring, to remove the hardened shavings, which sometimes adhere to and impede their cutting edges.

The cylinder bit cuts principally by the left corner of its edge, from whence its action gradually diminishes to the center, which, with the other half is inoperative; it therefore requires a preliminary or clearing hole to be bored in the work, with one of the pointed drills, or with the hand drill fig. 459, Vol. II. The surface end of this hole is then enlarged with a right side tool, to the depth of about one sixteenth of an inch, the shallow recess formed being turned true, either slightly taper, or exactly to the diameter of the cylinder bit to be used. The one end of the bit is embraced by the true recess, and the other is supported by the point of the popit head, placing the bit exactly in the axial line at the moment it commences to cut, which position it maintains while boring to any depth. But it should be observed that in boring a hole, say of one inch diameter in hardwood, if it be attempted to use the one inch bit immediately after boring the clearing hole, the labor would be excessive, and both the bit and the work would heat from the friction, producing a roughened surface. The best result is attained by making the clearing hole about half an inch in diameter, and then using the three quarters, the seven eighths, and the one inch bits in succession; each then cuts only by the most effective portion of its edge, and also, only upon that part of the work having the greatest surface velocity, which favourable conditions produce the aperture rapidly and leave a very smooth result. The extreme working difference advisable in boring hardwood or ivory, allows the holes to be enlarged to the extent of about one third their diameter, for cylinder bits below half an inch; one quarter or rather less their diameter, for those from half to one inch; and still less in the larger sizes. The limitation also saves excessive wear upon the bits themselves, preserving them for their other important purpose, that of boring true holes of definite measures in wood or metal.