Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 119

The cutting edge is nearly always convex, as shown in all the types illustrated. The junction of the light and dark shading in many of the illustrations denotes the extent of the bevel. The object of having a curved cutting edge is not only to prevent the jar and damage which might be done by the too sudden stoppage of the rapid motion of the heavy head in separating a group of fibres, but also to facilitate that separation by attacking these fibres in succession. For, assuming the axe falls square on its work in the direction of the fibres, a convex edge will first separate two fibres, and in doing this it will release a portion of the bond which holds adjoining fibres. An edge thus convex, progressing at each side of the convexity which first strikes the wood, facilitates the entrance of successive portions from the middle outwards. If the edge had been straight and fallen parallel to itself upon the end of the wood, none of this preliminary preparation would have taken place; on the contrary, in all probability there would have been in some parts a progressive condensation of fibres, and to that extent an increase in the difficulty of the work. The wedge-form of axe generally, but not always, has equally inclined sides. Assume that one face only is inclined, and that the plane of the other is continuous to the edge; now in striking a blow, it is obvious that the plane in the line of the fibres cannot cause any separation of these fibres, but at the other side of the axe the slope entering the wood will separate the fibres on its own side. For some work, the axe with unequally inclined faces may be preferable, for instance in chopping the projecting corners from a square log in preparing it for the lathe; this tool (Fig. 341) would do the work with greater ease to the workman, and with a higher finish than would the common hatchet with equally inclined sides. Coach-makers have much of this class of hatchetparing work to do, and the tool they use is bevelled on one side only; under where the handle enters the eye in a coachmaker’s axe (see Fig. 341) is a projection rising towards the handle; on this the finger of the workman rests in order to steady the blade in its entrance into the timber in the plane of the straight part of the blade, and to counteract the tendency of the wedge side pressing the hatchet out of its true plane. Carpenters and joiners may perhaps profit from a brief study of this tool used in a branch of woodworking different from their own. It is very evident, in using an axe, that different conditions of edge are requisite. There is much less resistance to the entrance of the edge when the blow is given in the direction of the fibre than when the blow is across that fibre. So great, indeed, may this difference become, that, whilst in the one direction the edge of the axe continues sound and efficient, yet a, few blows on the same timber at right angles to this direction seriously damages the edge. These remarks apply only to axes and hatchets used in dividing materials, and not to those used in merely preparing surfaces. The mode in which the axe is used will explain why it is unsuited for work across the fibre. The axe is simply a wedge, and therefore arranged to cleave rather than to cut the wood. Now, a calculation of the pressure necessary to thrust forward a wedge, and the impact necessary to cause the same wedge to enter the same depth, would explain why (regarded as a wedge only) the handle proves an important adjunct to the arm of the workman. This may be tested with an ordinary-handled hatchet on a soft straight-grained wood, or with a small axe with a straight and not a curved edge. Let it rest upon a lump of moderately soft clay; add weights until it has sunk to any desired depth, then take the axe by the head and by pressure force the axe to the same depth. Next hold the axe by the handle, first at, say, 1 ft. from the head, then at 2 ft., then, perhaps, at 3 ft., and give blows which seem of equal intensity, and mark the depth. Thus a practical testimony to the value of a handle will be shown by the respective depths.

Fig. 335.—Suffolk Axe Head.

Fig. 336.—Kent Felling Axe Head.

Fig. 337.—Handle of Felling Axe.

Fig. 338.—American Axe Head.

Fig. 339.—Kent Hatchet.

Fig. 340.—Canadian or American Hatchet.

Fig. 341.—Coachmaket’s Side Axe Head.