If we drive an axe, or a thin wedge, into the center of a block of wood, as at a, fig. 318, it will split the same into two parts through the natural line of the fibres, leaving rough uneven surfaces, and the rigidity of the mass will cause the rent to precede the edge of the tool. The same effect will partially occur, when we attempt to remove a stout chip from off the side of a block of wood with the hatchet, adze, paring or drawing knife, the paring chisel, or any similar tool. So long as the chip is too rigid to bend to the edge of the tool, the rent will precede the edge; and with a naked tool, the splitting will only finally cease when the instrument is so thin and sharp, and it is applied to so small a quantity of the material, that the shaving can bend or ply to the tool, and then only will the work be cut or will exhibit a true copy of the smooth edge of the instrument, in opposition to its being split or rent, and consequently showing the natural disruption or tearing asunder of the fibres.
In fig. 318 are drawn to one scale several very different paring-tools, which agree however in similitude with the type, b, fig. 316, page 460, and also corroborate the remark on page 462, that "in the paring-tools, the one face of the wedge or tool is applied nearly parallel with the face of the work." In tools ground with only one chamfer, this position not only assists in giving direction to the tool, but it also places the strongest line of the tool exactly in the line of resistance, or of the work to be done.
For example, the axe or hatchet with two bevils, a, fig. 318, which is intended for hewing and splitting, when applied to paring the surface of a block, must be directed at the angle a which would be a much less convenient and less strong position than b, that of the side hatchet with only one chamfer; but for paring either a very large or a nearly horizontal surface, the side hatchet in its turn is greatly inferior to the adze c, in which the handle is elevated like a ladder, at some 60 or 70 degrees from the ground, the perefence being given to the horizontal position for the surface to be wrought. The instrument is held in both hands,whillst the operator stands upon his work in a stooping positions, the handle being from twenty-four to thirty inches long. and the weight of the blade from two to four pounds,
The adze is swung in a circular path almost of the same curvature as the blade, the shoulder-joint being the center of motion, and the entire arm and tool forming as it were one inflexible radius; the tool there-fore makes a succession of small arcs, and in each blow the arm of the workman is brought in contact with the thigh, which thus serves as a stop to prevent accident. In coarse preparatory works, the workman directs the adze through the space between his two feet, he thus surprises us by the quantity of wood removed; in fine works, he frequently places his toes over the spot to be wrought, and the adze penetrates two or three inches beneath the sole of the shoe, and he thus surprises us by the apparent danger yet perfect working of the instrument, which in the hands of the shipwright in right in particular, almost rivals the joiner's plane; it is with him the nearly universal paring instrument, and is used upon works in all positions.
The small Indian adze or Bassoohah d, fig.318 , in place of being cicular like the European adze, is formed at a direct angle of about 45 or 50 degrees; its handle is wry short, and it is used
With great precision by the nearly exclusive motion of the elbow joint.* In order to grind either of these adzes, or percussive
*This very useful instrument (says Sir John Robison), vanes a little in different districts, in weight and in the angle which the cutting face forma with the lino of the handle, but the form shown is the most general, and the weight averages about chisels, it is necessary to remove the handle, which is easily accomplished as the eye of the tool is larger externally as in the common pickaxe, so that the tool cannot fly off when in use, but a blow on the end of the handle easily removes it.
The chisel e, admits of being very carefully placed, as to position, and when the tool is strong, very flat, and not tilted up, it produces very true surfaces as seen in the mouths of planes. The chisel when applied with percussion, is struck with a wooden mallet, but in many cases it is merely thrust forward by its handle. It will shortly be shown that various other forms of the handle or stock of the chisel, enable it to receive a far more defined and effective thrust, which give it a different and most important character. The paring-knife, fig. 8, p. 26, Vol. I, exhibits also a peculiar but most valuable arrangement of the chisel, in which the thrust obtains a great increase of power and control; and in the drawing-knife, the narrow transverse blade and its two handles form three sides of a rectangle, so that it is actuated by traction, instead of by violent percussion or steady thrust.
The most efficient and common paring-tool for metal, namely f, has been added to fig. 818 for comparison with the paring-tools for wood; its relations to the surface to be wrought are exactly the same as the rest of the group, notwithstanding that the angle of its edge is doubled on account of the hardness of the material, and that its shaft is mostly at right angles, to meet the construction of the slide rest of the lathe or planing machine.
The chisel, when inserted in one of the several forms of stocks or guides, becomes the plane, the general objects being, to limit the extent to which the blade can penetrate the wood, to provide a definitive guide to its path or direction, and to restrain the splitting in favour of the cutting action.
In general, the sole or stock of the plane is in all respects an
1 lb. 12 oz. The length of handle is about twelve or thirteen inches, and in use it is grasped so near the head, that the forefinger rests on the metal, the thumb nearly on the back of the handle, the other fingers grasp the front of it, the nails approaching the ball of the thumb. The wrist is held firmly, the stroke being made principally from the elbow, the inclination of the cutting face being nearly a tangent to the circle describod by the instrument round the elbow joint as a center, the exact adjustment being made by the grasp and the inclination of the wrist, which is soon acquired by a little practice. In this way very hard woods may be dressed for the lathe with a degree of ease and accuracy not attainable with the small axe used in this country." accurate counterpart the form it is intended to produce, and it therefore combincs in itself longitudinal and the sections, or the two guides referred to in the theoretical diagram, page 464, and the annexed figure 319, the parts of which are all drawn to one scale, may be considered a parallel diagram to 317, page 464, so far as regards planes.