The grindstone should be kept in order so far as possible by the equal distribution of the wear; narrow tools especially, should be constantly traversed across the face of the stone to avoid wearing the latter into ridges, and the extreme edges of the stone should be exposed to their fair amount of work, or otherwise the stone will become hollow and unfitted for grinding broad flat tools. By the equal application of the tools, the face of the stone may be kept tolerably flat with but little recourse to turning or hacking, which processes have been explained in the preceding catalogue under the head Wheels, articles 14 to 17. When however the stone loses its circularity, or becomes eccentric from being worn irregularly, it is better at once to resort to one of the means of correction, as otherwise the stone becomes rapidly worse, and the difficulty of holding the tools steady is considerably increased.
As a more scientific way of keeping grindstones in order, it has been proposed that two grindstones should be mounted with their axes parallel, and adjustable by a screw to keep their surfaces always in contact, and by giving them different surface velocities they would respectively abrade and correct each other, but the contrivance although simple is too refined for the majority of the grinders' shops, and is scarcely required for the limited purposes of the amateur.
The flat side of the stone is but little used notwithstanding that its broad surface appears so suitable for the purpose, but which is certainly not the case, in the first place the spindle would be found to be in the way of large tools or their handles, and secondly, the constant reduction of the stone arising from the friction of the work rubbing away its granular particles, would soon cause the flat surface to degenerate into an imperfect cone, and would leave a lump in the center, or if the stone were kept perfectly flat, it would be at the expense of its thickness, and the wedges by which it was at first secured, would be gradually exposed and loosened.
The stone is turned either to or from the operator according to circumstances, and in all practical cases it is best that it should run towards the extreme edge of the tool, and not from it, as in the latter case the last portion bends away from the stone and leaves a film or wire edge upon the tool, which the reverse direction avoids. The edges of the tools should be always ground parallel to the axis of the stone, or transversely, and not in the direction of their length, as the former position makes their edges concave to the same radius as the stone, and therefore keener and better prepared for the action of the oilstone.
In grinding the ends of rectilinear tools the stone should run towards the operator, as in turning, and for their sides or edges, it is perhaps the most convenient that the stone should travel the reverse way or backwards. Pointed tools are ground much the same as flat tools, but the choice of method is in some respects a matter of personal convenience.
In grinding the bevils and edges of instruments in their manufacture, the workman is seated on a board called the horse, and generally rests his elbows on his knees for steadiness, as explained on page 1106. The work is mostly applied to the stone by the hands alone without the employment except in rare cases of any guide beyond the sense of touch, which some of these workmen possess very acutely, and the amateur will find it desirable and sometimes imperative to trust to the feel alone in holding the tool upon the grindstone.
To grind the various tools with an uniform bevil requires considerable practice, as of course the least variation or tremor of he hand makes a corresponding irregularity in the bevil, after a time however the fingers acquire considerable sensibility and readily appreciate when the tool lies fair and flat upon the stone. In some cases even the practical men apply the tools upon a guide block that bears the same relation to the periphery that should exist between the respective edges of the tools, that is, if he edge of a tool is required to be exactly at right angles to the broad surface of the same, the guide upon which it is applied should point directly to the axis of the stone, or be as a radius. If the tool should differ 10 or 20 degrees from the right angle, the rest is inclined upwards or downwards to the same angle. There are also instruments in which the rectilinear tool is grasped, so that the end to be ground forms with the two legs of the instrument a triangular base, the feet are applied to some fixed plane surface, and the tool or the third leg rests upon the grinding surface. These instruments will be described in Section III.
The broad flat surfaces of tools are traversed quickly to and fro upon the top of the grindstone, as a short period of rest would grind a hollow place of the same curvature as the edge of the stone, and it is to lessen this evil as far as possible that the largest stones are employed for saws, the sides of which are required to be flat and parallel. In the razor on the other hand the curvature is desirable, and the four inch stone is there the nominal desideratum, still smaller grindstones are very often employed.
The following examples of the mode of grinding a few of the most usual tools for wood and metal, will explain the methods pursued by artizans generally for grinding the edges of their tools; and which differ from the practices of the cutler, and grinder, only so far as is called for by the nature of their respective apparatus.
In grinding an ordinary plane iron the stone travels towards the operator, and the tool is applied about half way up the stone from the axis, the rest is not generally used, but the iron is grasped firmly in the right hand to guide the tool, the position of the hand being the same as that for sharpening the tool explained in page 1144 while the pressure is principally given with the fingers of the left hand applied near the edge of the tool. The iron is inclined vertically so that the chamfer may be ground to the angle of about 25 degrees with the face of the blade, but horizontally the iron should be held quite square to the face of the stone, or parallel with its axis, in order to prevent either corner being reduced below the proper line. To assist the inexperienced in determining when the plane iron is held square, the top iron is sometimes kept on during the grinding, but it is set back about one eighth of an inch from the edge, so as to be quite out of the reach of the grindstone, as the action of the top iron would be materially injured, or altogether spoiled, if its form were interfered with, it is however a safer and more cleanly method to remove the top iron before grinding.