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.
The plane, in its simplest form, consists of a chisel inserted at an angle into a box, generally of wood, and with the cutting edge projecting through the bottom of the box. If the actions of a workman be noted as he is smoothing wood with a chisel alone, it will be seen that he holds the bevel edge on the wood, and so elevates or lowers the handle as to secure a proper and efficient cut. Then he advances the tool in a line at right angles to its cross section. If now, instead of thus continuing to hold the tool, the chisel was so fixed in a movable piece of wood as to be at the same angle as the workman required, then if the mouth were broad enough, and the instrument were propelled along the wood, a shaving would be removed very nearly the same as that obtained from the chisel alone. In the arrangement thus sketched, the workman would be relieved from the care needed to keep the tool at a constant angle with the surface of the timber. There is, however, a fixity of tool here, and consequently an optional or needful adjustment called for by any varying condition of the problem cannot be had. "When operated upon by hand alone, if an obstacle to the progress of the tool is presented, as, for instance, a twist or curl in the fibre or grain of the plank - the presence of a knot - then the workman by hand can adjust the handle, and so vary the inclination of the cutting edge as the circumstances of the case require.
Not so if the tool is securely fixed in a box as described. Whilst therefore one gain has been had, one loss has been encountered. Observe the defects of the primitive plane, as hitherto described, and note what hopeful elements it contains.
The front of the sole of the box will clearly prevent the penetration of the encased chisel into the wood, because it cannot now be drawn to follow the fibre should it lead inwards. Suppose, however, that in the progress of the work such a place has been reached as would have so drawn the chisel inwards : either the strength of the indrawing fibre will be so great that the workman will be unable to propel the tool, or, if not thus impeded, he must by extra effort separate the fibre and so release the tool. This separation, however, may not be by the process of cutting, but by that of tearing, and shavings so torn off will have left their marks in the roughnesses which attend the tearing asunder of fibrous woods. Thus the tool will defeat the very purpose for which it was designed. To obviate the difficulty described has exercised much ingenuity, and led to more than one contrivance in planes as generally used.
The causes which so forcibly draw, or tend to draw, the tool downwards below the surface of the timber are the hand of the workman and the tenacity of the fibre. If the tenacity is greater than the power, the workman must stop. That the tool cannot follow the direction of the fibre is clear, because the front part of the wooden sole forbids the penetration, but that it may be brought to a standstill, or must tear off the fibre, is also very clear. The mechanician has therefore to consider how to defeat these tendencies which, as now sketched, result from a collision between the indrawing strength of the fibre and the power of the man to cross-cut the fibre by the tool, or else to tear it asunder and leave the surface rough. Since the tool, as now contrived, cannot efficiently cross-cut the resisting fibre, and since that fibre has to be removed, the object must be either to prevent such an accumulation of fibres as will stop the progress of the tool, or to destroy the fibre piecemeal as it is operative for hindrance. Both plans have been adopted.
A consideration of the former may prove introductory to the latter, which appears in almost all attempts to perfect this tool and its appended contrivances.
As the tool progresses, and the fibres become more and more impeding, it will be-clear that a portion of this impediment results from a condensation of the fibre in the mouth of the wooden box. The more numerous the fibres admitted lure, the greater will be the condensation. This state of affairs can be partially obviated by a narrowing of the mouth of the plane; such an act of course requires that the introduced chisel should enter less deeply into the timber being operated upon. Although thus abated, the cause is not removed, and even if so far abated as to prove no real impediment to the workman, yet the quantity of material removed on each occasion will be so small that the tool becomes one for finishing work only, and not for those various operations to which its present powers enable artisans to apply it. To be the useful tool it is, the mouth must not be so narrowed, nor the inserted chisel so withdrawn, that the shaving is thus the thinnest possible. This led to a contrivance now almost universal, that of breaking the fibre so soon as it is separated from the piece of timber.
The designer seems to have considered that as soon as a short length of shaving had been removed, it would be well to destroy the continuity of the fibre, and so prevent an accumulative resistance from this cause. Hence, instead of allowing the cut-off fibres to slide up the inserted chisel, he bent them forward, in fact, cracked them, and so broke the cumulative indrawing force of them. This he accomplished by the use of what is now called the "back iron," and from henceforth the boxed-in chisel loses its identity, and must be regarded as part of an independent tool.
The tool thus built up is called a plane. Three forms are in general use in English workshops, called the "jack," the "trying." and the "smoothing" plane. These are on the bench of all workers in smooth straight surface wood. Although externally alike except in size, they are yet used for different purposes, and each has a specialty in its construction. These specialties may now be considered.