Work must never be done with blunt or badly-set tools. Tools must always be kept sharp and in good order.
These rules should always be kept in mind. Many a slojder toils in the sweat of his brow with a blunt saw, or a badly set blunt plane, rather than take time to put his tool in order, though tools in good condition save hours of work, much unnecessary trouble, and needless vexation. Blunt tools demand more strength and exertion than sharp ones, and seldom, if ever, produce such good results. The rules given above are especially important in the case of children, for whom work ought not to be made unnecessarily difficult.
The sharpening of edge-tools is performed on the grindstone and the oilstone. The method of sharpening a saw has already been described (pp. 80, 81).
The ordinary Grindstone consists of a circular slab of sandstone, which rotates on an axle, and is provided with a handle for turning. It is supported on a grindstone stand or bench. Below the stone is a wooden well, lined with zinc, partially filled with water, into which the stone is sunk about one inch when in use. The stone should not be too fine in the grain or too hard.
The grindstone should never be used dry, because the steel does not "catch " well unless the stone is wet, and the friction on a dry stone " burns " the steel and makes the edge of the tool soft. Exposure to the sun for any length of time makes the stone too hard, while prolonged immersion of any portion of it in water renders that portion soft. Consequently it wears faster, and the stone becomes uneven or eccentric. The stone should therefore be kept dry except when in use.
A frame-work attached to the stand prevents splashing when the stone rotates by directing the water down into the well, and splashing may still further be avoided by fastening a thick piece of stuff in front so that it trails upon the stone and absorbs a portion of the surplus water. The stone must always be turned towards the worker and towards the edge of the tool, which must be moved steadily, and with equal pressure from side to side, across the whole breadth of the stone, to prevent the formation of scratches or depressions on its circumference. The bevelled edge produced by grinding must present either a flat or a concave surface to the convex surface of the stone. It must never be convex. The concave form of the bevelled edge is advantageous, because it materially lightens the final sharpening on the oilstone. The edge must also be quite straight unless a curved edge is actually required.
Care of the grindstone.
As it is difficult, especially for the inexperienced, to hold the steel steadily enough against the stone, a grinding support has been invented. Such a support of American make is shown in Fig. 84. It consists of an iron frame into which the plane-iron or the chisel is screwed. A small wheel below the frame revolves upon the grindstone, and the desired angle on the edge of the tool is obtained by fastening it in with the edge at a shorter or longer distance from the frame. By means of this simple contrivance even an inexpert pupil is able to grind a plane-iron correctly.
Fig. 84. Grinding support. 1/3.
A very common fault in grinding is to make the angle which the bevelled edge makes with the face of the tool too great, i.e., to make the edge too thick. This is often done by beginners in their haste to be relieved from grinding.
The tool must be ground till a raw edge appears, i.e., the very thin "film " or hair produced by the grindstone's removing the very edge of the steel. This, in its turn, is removed by the oilstone.
Sharpening with the oilstone is necessary, because the edge produced by the coarse-grained grindstone is neither fine enough nor even enough for immediate use.
The raw edge.
Fig. 85. Oilstone and case. 1/4.
The oilstone is a slab of specially finegrained stone. "Washita" and "Arkansas" stones from America, and "Turkey" stones are the best. [Welsh oilstones are less expensive, and can thoroughly be recommended.- Trs.] The oilstone should be 8 inches long and 2 1/2 inches broad, and it should be kept in a wooden box with a cover (Fig. 85). A good oilstone is very hard and close-grained, and it " takes well," i.e., it acts almost like a very fine file on the steel. The colour is yellowish-white. They last a long time, but are expensive to buy.
The best oilstones.
When in use, the oilstone should be moistened with vegetable oil. The addition of a little paraffin is an improvement. The tool is held in both hands, and the bevelled edge is applied closely to the stone in such a way that, while the bevel is altogether in contact with the stone, the edge presses rather more heavily on it, and this angle of inclination must be steadily maintained to prevent the edge from becoming rounded. The steel is now drawn over the stone with a slow, steady, backward and forward motion. When this has been repeated often enough, it is turned over and passed once over the stone with the face flat. The worker must not confine his operations to the middle of the stone, but must use the whole of the surface.
Method of using the oilstone.
An oilstone slip, i.e., a piece of the same kind of stone as the oilstone, but smaller and thinner, and rounded at the edges, is required for the sharpening of gouges, spoon-irons, etc.
Sharpening must be continued until the edge itself is not visible when held up against the light, or until it no longer appears white and rounded. Its sharpness is tested by touch ing it lightly with the finger.
A sharp edge.
For the benefit of those who wish to procure a tool cupboard, complete drawings of one are given in Plate XI. It is so arranged that every tool has a fixed, easily observed place, in order that the absence of any may be readily discovered when the tools are laid past. Tools must further be so arranged that when one is taken out another is not dis-placed; and all sharp edges must be protected.
Any alterations in the size of the cupboard, required by a larger or smaller stock of tools, could easily be made.