Fig. 2746.
[Fig. 2745] represents the form of handle for a paring chisel, its total length being 6 inches, and from a to b being 11⁄2 inches. The diameter at c is 11⁄2 inches, the hollow below d of 3⁄8 of an inch radius, the diameter at d 1 inch, and the length from b to e 11⁄2 inches. This form affords a firm grip to the hand, the end e being applied to the operator’s shoulder. The shape of handle for a firmer chisel is shown in [Fig. 2746].
Chisels require great care both in grinding and oilstoning them, being held very lightly upon the grindstone when finishing the grinding so as to avoid as far as possible the formation of a long feather edge. The flat face of the chisel should never be ground, as that would make it rounding in its length, hence there would be nothing to guide it in cutting straight and the value of the tool would be almost destroyed.
In oilstoning the chisel, great care is necessary in order to avoid forming a second facet at a different angle to that at which it was ground, because such a facet is too narrow to form any guide whereby to move the chisel in a straight line, and the consequence is that the edge is oilstoned rounding and cannot do good service. The whole length of the ground facet or bevel should rest on the oilstone, but the pressure should be directed mainly to the cutting end so that at that edge the oilstone will entirely remove the grinding marks, which will, however, remain at the back. If there is at hand a grindstone of sufficiently small diameter, the chisel may be made hollow on the bevel, as shown in [Fig. 2745a], so that when laid on the oilstone the bevel will touch at the back and at the end only, and this will enable the chisel to be pressed evenly down on the stone, thus producing a very even and flat edge, while leaving but a small area to be oilstoned.
The motion of the hands should not for the oilstoning be simply back and forth, parallel with the oilstone length, but partly diagonal, which will assist in keeping the chisel level. The back of the chisel should be laid flat upon the oilstone and moved diagonally, under a light pressure, which will remove the wire edge, which may be further removed by lapping the chisel on the operator’s hand.
Fig. 2747.
Chisels for turning work in the lathe are best if made short, and to enable the cutting edge to get up into a corner, the chisel is sometimes given two cutting edges, as at a, in [Fig. 2747], the edges forming an angle, one to the other, of less than 90°. For finishing curves in the lathe the chisel shown at b in the figure is employed, or for deeper work, as in the bores of holes, handles are dispensed with, chisels being formed as at c and d in the figure.