In using this instrument, the tool to be sharpened is laid face downwards upon the horizontal plate, and with the side of the tool in contact with the guide bar, which is fixed at the angle required for the horizontal edge of the tool, the second plate is then adjusted to give the required bevil to the chamfer of the tool. The oilstone moistened with a few drops of oil is applied with its face flat upon the vertical plate, and the tool is advanced with the fingers of the left hand, until its end touches the oilstone, which is rubbed in contact with the vertical plate in all directions by the right hand, while the end of the tool is kept gently pressing against the oilstone, this is continued until the chamfer of the tool is sufficiently sharpened. If it be an angular tool the position of the guide bar is then changed, and the second chamfer is operated upon in the same manner; and lastly the face of the tool is laid flat on the oilstone, and gently rubbed to remove any trifling burr that may have formed upon the edge. It is of course necessary that the tool should be held quite steadily in its position on the bed of the instrument, notwithstanding that it is kept constantly pressed endways against the oilstone.

Angular tools that are used for rose engine turning on curved surfaces such as those of watch cases, are generally ground with the one angle of the edge of nearly twice the length of the other, this is done to give the tool increased strength, and allow of a rubber with a rounded end being fixed near to the point of the tool, to regulate its penetration.

The various small tools with straight and angular edges, employed for eccentric and ornamental turning, are required to have very accurate, keen, and highly polished edges, in order that they may impart the same degree of excellence and finish to the work, whether executed with tools fixed in the slide rest, or with revolving cutters employed in the various apparatus that will be described in a future volume. These ornamental works, from their intricate and delicate character, scarcely admit of any polishing, and therefore the beauty and finish of their surfaces depend almost exclusively upon the perfection of the cutting edges of the tool, as the good or bad quality it may possess, is literally copied upon the work, without the possibility of subsequent correction. It is therefore highly desirable that the edges of the tools should be formed by perfectly true planes, polished in the most careful manner, results which cannot be obtained without the assistance of suitable guides for holding the tool, and the employment of the most delicate abrasive powders.

The instrument for setting straight and angular tools for ornamental turning shown in fig. 1047, resembles in principle and construction the instrument for grinding common turning tools on the revolving lap, described on page 1159, but fig. 1047, has greater range in the angles to which the tools may be set, and it is also provided with a more suitable socket for the reception of these small tools, which are made of one uniform size in their shanks or stems, in order that they may all fit the same socket of the sliding rest in which they are to be used. Fig. 1047 is employed in the reverse manner to the instrument for grinding common turning tools, as instead of the tool being held stationary upon a revolving lap, the tool when fixed in the instrument for angular tools, is rubbed first upon a stationary piece of oilstone, and subsequently set and polished in like manner upon flat plates of metal supplied with oilstone powder or crocus.

The case for containing the instrument for setting angular tools, has three slabs of mahogany, measuring about eight inches long, and six and a half inches wide, fitted as drawers; into the one side of each of the drawers, and close to the edge, are inlaid respectively, a piece of oilstone, brass, and cast iron, about three and a half inches, by three inches. The upper surfaces of these plates are made quite flat, and they project slightly above the wood as shown in fig. 1047, in which the one edge of the angular tool is supposed to rest upon the metal plate, whilst the two feet of the instrument stand upon the mahogany slab, which is sufficiently large to support them whilst the tool is traversed in all directions over the metal plate.

Fig. 1047.

Sharpening Cutting Tools With Artificial Grinders  30021

In fig. 1047, the same letters of reference are used for corresponding parts as for fig. 1042, and the description of the latter instrument on page 1160, is equally applicable to fig. 1047, except that the graduated arc on C, is extended to 75 degrees on each side of the central line, and the socket G is made as a straight bar with two projecting pieces having rectangular openings to fit the shafts of the tools, which are fixed by the binding screw l. To sharpen an angular tool of 30 degrees, the instrument is adjusted as shown in fig. 1047. The index point of the socket G, is placed at the division marked 30 on the arc C, which is then adjusted on the vertical arc B, to the angle required for the chamfer of the tool; in the drawing this is supposed to be 30 degrees, the tool is then placed in the socket G, and the distance which it should project from the socket, is determined by placing the instrument in the position shown in the figure, with its two legs upon the wood surface, and the edge of the tool resting upon the oilstone. The projection of the tool is then so regulated that the base piece A, may be parallel with the wood surface, when the tool is fixed by the binding screw l. Should the projection of the tool be such that the base of the instrument is inclined to the wood surface, the chamfer of the tool would not be ground to an angle of 30 degrees; the precise angle of the chamfer is however not generally very important.

The instrument having been adjusted, the next operation is to sharpen the tool upon the oilstone, which is moistened with a few drops of oil, and the tool is applied as shown in the drawing, and lightly rubbed with circular or elliptical strokes in all directions over the surface of the stone, until a keen edge is produced upon one angle of the tool. The index point of the socket G is then shifted to 30 degrees on the opposite side of the circle of graduations on the piece C, and the second edge of the tool is sharpened in the same manner.