Now put the sharpest edge-tool you can find under a powerful microscope, and you will see that the edge, instead of being so very smooth, is really quite ragged,—a sort of saw-like edge. Then look at the structure of a piece of wood as roughly indicated in Fig. 6, and you will understand at once just what we do when we cut wood with an edge-tool. You see the microscopically small sticks or tubes or bundles of woody fibre of which the big stick is composed, and you also see the microscopically fine saw to cut them. Now if the edge of the tool is fine you can often do the work satisfactorily by simply pushing the tool straight through the wood, but do you not see that if you can draw or slide the tool either back or forth the edge, being saw-like, will do its work better?
This stroke cannot be used of course in chopping with the axe or hatchet, splitting kindling-wood, or splitting a stick with the grain with a knife or chisel. In these operations the main principle is that of the wedge, pure and simple, driven through by force, the keen edge merely starting the cut, after which the wedge does the rest of the work by bearing so hard against the wood at the sides of the cut that it forces it to split in advance of the cutting edge, as in riving a log by the use first of an axe, then of an iron wedge, and finally a large wooden wedge (Fig. 8).
Fig. 8.
Practical directions and suggestions about the different Tools and their Uses and the various Operations will be found alphabetically arranged in [Part V].
CHAPTER III
WOOD
Before you can make anything successfully, you must have not merely wood, but the right kind of wood for the purpose. There are, also, "choice cuts" in lumber, as the butcher says of meat, and judicious selection of the stock often makes all the difference between a good job and a poor one; so let us examine a log and follow it through the sawmill.
