Cylindrical openings to fit corresponding pins or short cylinders, for the purpose of attaching one part of the work to another, usually of inconsiderable depth compared with their diameter, are produced with the turning tool. The smaller are commenced by a fine hole, made by the wire drill first mentioned; the larger, by the hand drill fig. 459, Vol. II.; the aperture is then enlarged with a right side tool, fig. 390, used upon the armrest. The tool is very narrow for the smaller holes, being usually a small size so far worn away by grinding, that the line of the cutting edge and that of the back meet in a long point, such a tool being preserved for the purpose. Small internal cylinders below and about one eighth of an inch in diameter, are too small to permit their parallelism to be tested by the callipers; they are therefore gaged by the pin itself, which is turned first, quite parallel, and the internal cylinder is hollowed and fitted to it. The callipers are easily used within internal cylinders of about one quarter of an inch diameter, and either these, or their external counterparts may be turned first, as the progress of the work may render convenient; the more general and safer practice however, is to turn the aperture first and to reduce the pin to fit it.
Internal cylinders from about two inches diameter upwards, may be roughly hollowed out with the gouge, used exactly as described for the same purpose in softwood ; but, as hardwood offers greater resistance to the tool, the gouge is only suitable x 2 for shallow works. The method fig. 422, applies to all depths and is more general. A hole is first bored with a hand drill to a depth about one eighth of an inch less than the intended length of the cylinder, that the mark left by its point, may be subsequently entirely turned away in finishing the internal surface. A right side tool held upon the armrest, is inserted in the hole and pulled towards the circumference, a succession of such cuts, removing the material to the bottom of the hole made with the drill. The traverse of the tool is principally effected by poising the weight of the body backwards to pull upon it, the rate, being gradually retarded from the center to the circumference, to allow the tool time to cut upon the increasing surface.
The depth to which the right side tool should enter the hole for every separate cut, varies with the hardness of the material, and the diameter of the work; two or three narrow cuts of about the eighth of an inch, the average width, being made in less time and leaving the work smoother, than when their combined width is taken as one cut. The tool is supported upon the armrest its edge held radial, by both hands in the usual manner, except in heavy roughing cuts upon large work, when the left hand is frequently withdrawn from the pedestal of the rest and clasped upon the shaft of the armrest, thumb uppermost, to assist in pulling the tool into cut. As the cylinder increases in depth, the right side tool more and more overhangs its point of support; raising the tee of the rest then affords some additional command over the tool, its shaft and that of the armrest then both slope a little downwards, more in the position of a tool held underhand. Large and deep cylinders are commenced in the same manner, and when they become beyond the convenient use of the armrest this and the tool are exchanged for a strong right side tool in a long handle, with the tee placed as in fig. 417, and sufficiently below the center to place the face of the tool about radial. The operator stands nearly facing the mouth of the cylinder, with the handle of the tool tightly pressed between the right upper arm and the side, just above the elbow. The blade of the tool is grasped by both hands, pressed closely together, one in front of the other, the right hand against the chest with the thumb, and the left hand with either the thumb or the knuckles uppermost. In this position, the shaft of the tool is at a slight horizontal angle in front of the right chest, lying flat upon the rest; and the separate cuts are made partly by the weight of the body, and partly by muscular pressure given on the side and also in the direction of the length of the tool.
Fig. 422. Fig. 423. Fig. 424.
The internal cylinder is finished, and the irregularities left by the separate cuts are connected into one straight line, by continuous shavings taken from the bottom outwards; the bottom or internal surface, being usually turned true or flat at the same time. During the finishing the cylinder is frequently measured with the inside ends of the callipers, fig. 342, and enlarged, by more frequent shavings at the back or front end, as may prove necessary. For works of moderate size the tool is used under the guidance of the armrest, but it no longer remains only in simple contact with it, as in the roughing cuts ; but sometimes, more especially in traversing the deeper end of the cylinder it slides upon it, the shaft of the tool being drawn outwards by the right hand, while the armrest blade remains nearly stationary on the tee of the rest. The armrest takes up the motion as the cut nears the mouth of the cylinder, the tool then. ceases to slide upon it, and is moved while cutting by the lateral traverse of the armrest upon the tee. For finishing large, deep works, the larger tool is supported on the tee alone, which is placed across the mouth of the cylinder.
In cutting these continuous shavings, the edge of the right side tool is apparently parallel with the side of the work, actually, it has a trifling horizontal inclination to prevent the corner leaving marks. The extreme end corner having slightly the most penetration, sufficient to cause the cutting action to diminish, and to cease entirely about half an inch down the side edge. The same amount of horizontal angle is maintained throughout each entire traverse, but less is required for the finishing cuts, when the straight side of the cylinder itself as it approaches truth, greatly assists the correct guidance of the tool. The continuity of the shaving is maintained by the pressure of the right hand upon the tool, always assisted by a gentle pull upon the armrest, whether the tool be stationary or sliding upon it. The thickness may be varied, by varying the pressure or by slightly twisting the handle of the tool while cutting, to give the edge more or less penetration.