This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Principles. Axes are tools to be used with both hands; they have long handles, and may be swung as sledge hammers. Hatchets are to be used with one hand, have short handles, are much lighter and thinner than axes, and are employed more in the trimming than in the hewing of timber. Both narrow and broad axes are employed in forestry, the woodman's choice being affected by the size of the timber and the character of the fibre. A hatchet is handled with the centre of gravity nearer the cutting edge than the line of the handle; an axe, with the centre of gravity in the line of handle produced. When we pass from the tool and its contrived handle to the mode of using, and the purpose for which it has been constructed, we find, as a rule, a cutting edge formed by 2 inclined surfaces meeting at an angle, the bisecting line of which passes through the middle of the metal. It is very apparent that the more acute this angle is, the greater, under the same impact, will be the penetrative power of the axe into the material against which it is driven.
This supposition needs to be qualified, for suppose the material offers a great resistance to the entrance of this edge, then the effect of the blow, upon the principle that action and reaction are equal, will react upon the edge, and the weakest, either edge of axe or object struck, must yield. Here experience would be obliged to qualify the simple tool in which the edge was keen and acute, and would naturally sacrifice the keenness and acuteness to strength. When early uses of the axe are considered, it will be noticed that even in fashioning with an axe or adze the same piece of wood, different conditions of edge are requisite. If the blow be given in the direction of the fibre, resistance to entrance of the edge is much less than in the blow across that fibre. So great, indeed, may this difference become, that whilst the axe seems in all respects a suitable tool, yet as the attention of the workman passes to directions inclined to the fibre at an angle of more than 45°, he will be induced to lay it aside in favour of the saw. These remarks apply only to tools used in dividing materials, and not to tools used in preparing surfaces of materials. This preliminary consideration prepares us for the different circumstances under which these 2 classes of tools may be respectively used.
And as the contrast of the effect of the same tool under different circumstances in the same substance is considerable, great also is likely to be the contrast between the edges of the tools and the manner of using them, e. g. the axe, which is the proper tool in the direction of the fibre, is operated upon by impact, whilst a saw, which is the proper tool across the fibre, is operated upon by tension or thrust, but never by impact.
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.
The motions of the hands on the handle of an axe are similar to those of a workman on that of the sledge hammer. The handle of a properly handled axe is curved, that of a sledge hammer is straight. For present consideration this curvature may be overlooked, although it plays an important part in the using of an axe with success and ease. If the almost unconscious motions of a workman skilled in the use of an axe be observed, it will be noticed that whilst the hand farthest from the axe head grasps the handle at the same or nearly the same part, the other hand, or the one nearest to the head, frequently moves. Let us follow these motions and consider the effect of them. The axe has just been brought down with a blow and entered between the fibres of the wood. In this position it may be regarded as wedged in the wood, held in fact by the pressure of the fibres against the sides of the axe; from this fixity it must be released, and this is usually done by action on or near the head. For this purpose the workman slides his hand along the handle, and availing himself (if need be) of the oval form of the handle after it has passed through the eye of the metal, he releases the head.
The instrument has now to be raised to an elevation; for this purpose his hand remains near to the head, so causing the length of the path of his hand and that of the axe head to be nearly the same. The effect of this is to require but a minimum of power to be exerted by the muscles in raising the axe; whereas if the hand had remained near the end of the handle most distant from the head, then the raising of the axe head would have been done at what is called a mechanical disadvantage. Indeed, if a workman will notice the position of the band (which does not slide along the handle) before and after the blow has been given, he will find that its travel has been very small indeed. Reverse the problem. Take the axe head as raised to such an elevation as to cause the handle to be vertical (we are dealing with ordinary axes, the handles being in the plane of the axe blade). Now the left hand is at the extremity of the handle, the right hand is very near to the axe head - the blow is about to be given. The requirement in this case is that there should be concentrated at the axe head all the force or power possible; hence to ease the descent would be as injudicious as to intensify the weight of the lift.
Consequently whilst with the hand nearest to the head (as it is when the axe reaches its highest elevation) the workman momentarily forces forward the axe, availing himself of the leverage now formed by regarding the left hand as the fulcrum of motion, he gives an impulse, and this impelling force is continued until an involuntary consciousness assures him that the descending speed of the axe is in excess of any velocity that muscular efforts can maintain. To permit gravity to have free play, the workman withdraws the hand nearest to the head, and sliding it along the handle, brings it close to the left hand, which is at the extremity of the handle; thus the head comes down upon the work with all the energy which a combination of muscular action and gravity can effect. The process is repeated by the right hand sliding along the handle, and releasing as well as raising the head.