Fig. 1029 represents an arrangement suitable for grindstones of from two to three feet diameter. In this case the frame is entirely of iron; the stone is worked by a treadle leading to the cranked spindle, mounted between centers; and instead of the stone being fixed to the spindle by wooden wedges, which are liable to be disturbed from their original setting by extreme change from wet to dry, they are secured by the improved plan, introduced by Holtzapffel & Co., of casting a lead center in the eye of the stone, by means of a proper mould, so as to leave a central and cylindrical aperture, and the spindle is turned to the corresponding diameter, and provided with a screw and nut, which press the stone against a flange on the spindle, which has a pin to ensure the rotation of the stone. In this manner the stone is fixed with great solidity, and with the power of removal from one spindle to another, when the reduction of the diameter of the stone calls for the change. Fig. 1027 is also mounted upon its spindle in a similar manner. The rest for the tools in fig. ] 029 admits of being placed at any height or distance from the stone that may be required, and a leather flap suspended from the rest serves the purpose of the splash-board, mentioned in the last paragraph.
A small grinding and polishing machine adapted for the use of the amateur is represented in fig. 1030. This machine is fitted with five spindles, two of them have grindstones, the one for rough usage, the other to be reserved for the more particular tools, the three other spindles are fitted with a metallic lap of lead hardened with a little antimony, a buff wheel with emery, and a circular brush. The spindles are driven by an iron foot wheel and treadle, somewhat after the manner of a lathe, as explained under the head Wheels in the catalogue, page 1104, article 7. The stones of about the diameter of 7 inches are fixed upon roughened iron spindles by means of melted lead poured in between the two; by this plan such small stones are not liable to be split, which frequently occurs with wooden wedges, either from their being over driven in the first instance, or from their subsequent expansion by wet.
The spindles were formerly made with centers at each end, and a pulley for every spindle, but they are now made with a center point at the one extremity, and a truncated cone with a driving pin at the other, and the spindles work respectively between a center screw and a hollow notched cone fixed in front of the pulley, which is free to revolve upon its own bearing, when connected by the band with the foot wheel and treadle beneath. By this arrangement which is somewhat similar to the center chuck and driver of the common turning lathe, the spindles can be readily exchanged, by unwinding the center screw, without the displacement of the band. The machine is provided with two iron rests for the tools, that are each applicable to the edges of the grindstones and the face of the lap, they are of different bevils and susceptible of adjustment by the screw. On the back of the cast iron trough is mounted a water cistern with drip valve, the water from which falls upon the stone slightly in advance of a piece of tow, held in contact with the stone by a clamp, this effectually prevents the water from being thrown off, by the centrifugal action, and keeps the stone uniformly moist. A box at the back of the frame serves to contain the polishing powders, brushes and scraper. The other parts of the apparatus will be sufficiently explained by an inspection of the figure.
The ordinary cutlers' wheel and the large grindstones for tools have been already described in the catalogue, pages 1105 to 1108, and their arrangement will be sufficiently obvious without the aid of diagrams. Large stones are however sometimes furnished with a contrivance called a dolly bar, for adjusting the height of the water in the trough without the continual necessity for adding small quantities to maintain it at the most suitable level, the dolly is a large wooden bar suspended from a pulley attached to the splash board, and partially immersed in the water, when the dolly is lowered it causes a corresponding elevation of the water so as just to reach the grindstone. This contrivance in common with all those of the grinder is exceedingly simple, and although dirty the grindery is often very picturesque.
The restoration of the edges of most cutting tools for wood and soft substances is effected by the successive action of the grindstone and oilstone, the former being employed to remove the principal bulk of the material, so as to prepare the tool for the action of the slower but more delicate oilstone, which produces a much keener and more accurate edge than can be obtained with the grindstone. Tools for cutting the metals and hard materials are frequently left from the grindstone without the application of the oilstone, which is chiefly resorted to for setting a smooth edge upon the finishing tools.
Tools that are required to possess a delicate edge of a definite form, should in all practicable cases be ground upon the one bevil only, the second face then admits of being carefully formed in its manufacture, and the accuracy thus given should be scrupulously maintained, as it is clearly much easier to produce the required form by the abrasion of the less important face, than when both angles of the edge have to be renewed every time the tool is sharpened. For example, the axe and chipping chisel which require considerable strength, and but a moderate amount of accuracy, are commonly ground with two bevils, while the plane iron and paring chisel, which require accurate edges and greater delicacy, have the one face made quite level in the first instance, and in the process of sharpening, the second face of the angle is alone operated upon; in screw tools, and moulding tools for turning, this is still more imperative. The razor, which requires delicacy of edge rather than accuracy, is sharpened on both faces, but in this case as will be shown hereafter the back of the instrument serves as a guide for the formation of the edge.