Let us now consider, therefore, what are the conditions necessary to the efficiency of these tools. Planes will work badly from three or four causes, and a workman who tries to maintain their efficiency at as high a standard as possible will sometimes have to give attention to each of these in turn before he can find the causes of their degeneracy, and rectify them. In the first place, since the value of a plane, as such, depends on its embodiment of what is termed the ” guide principle,” whatever produces inaccuracy in the face or sole must interfere with the correctness of its working. The soles of all planes, whether they have wood or iron stocks, lose their accuracy in the course of time bathetic of wear, and in the case of the former, sometimes by the warping of improperly-seasoned stuff. In the case of an iron plane, want of truth can only follow on long-continued use, and then the file and scrape must be resorted to for the restoration of the original accuracy. With wood planes, the wear of a few months only is sufficient to necessitate the truing-up, or ” shooting,” as it is called, of the sole.
This is performed as follows :
- First as-certain, by means of winding strips and straightedge, the precise extent to which the sole is winding, or rounding, or hollow, and also the localities of the highest portions.
- Keep the cutting-iron wedged in place, but knocked back about kin. from its proper position, and screw the plane with its face upwards, in a bench-vice.
Double Plane Iron
Sharpen and set the iron of another trying plane very fine and very true transversely, and with it remove a few ribbon-like shavings from the highest portions of the sole of the plane which is screwed in the vice. Before reducing the whole surface, try the strips and straightedge, repeating the test three or four times if need be, the aim being to get as true a face as possible while reducing the thickness of the stock to as slight an extent as is necessary, because with each reduction in thickness the mouth of the plane is correspondingly widened. When the face shows a general dead level, even though a small patch or two of the original face may remain unmoved, it is wise to stop, because a localized depression here and there will not affect the general truth and accuracy of operation of the plane, while rapid widening of the mouth, due to excessive reduction of the face, is always an evil to be postponed as long as possible. After the face is “shot,” saturate it with linseed oil, to smooth and harden the grain and impart a glossy skin. After the maintenance of the truth of the bottom face, comes the grinding, sharpening, and setting of the iron. This, in most wooden planes, is double, that is, there is a lower or cutting iron and an upper or non-cutting iron, the two being clamped together with the screw. The function of the top iron is the imparting of rigidity to the bottom one, by which its tendency to ” chatter ” is reduced, this tendency being inseparable from its mode of setting at an angle in the stock, while a true chisel should have its cutting face coincident, or nearly so, with the face of the material upon which it is operating.
The top iron stiffens the lower, and prevents the vibration which would other-wise ensue, causing choking of the mouth, or a rough, uneven surface to be left by the plane. In some degree, also, it helps to prevent tearing up of the grain, by breaking and turning over the shavings immediately that they leave the cutting edge. Besides the setting of the top iron, results are affected by the mode of grinding and sharpening of the cutting iron, the bedding of the latter on its seat and wedging of the same, and the width of ” mouth,” or opening in the sole, through which the iron projects. The cutting-iron may be ground and sharpened either too thin or too thick. In the latter case, its proper wedge-like action will not come into play, and the surface of the material will be rubbed, scraped, and cut in turn, much labor being expended with little good result.
If, on the other hand, the iron is ground and sharpened too thin, it will not retain its edge, but after the removal of a very few shavings, especially in harsh, hard, and knotty stuff, it will become finely notched and leave grooves and scratches over the surface. In each extreme also the tendency is to cause the shavings to choke in the mouth. Hence the happy mean is to grind and sharpen at such angles that the iron will not only cut sweetly and freely, but retain its edge for a reasonable length of time. These angles should depend to some extent upon the nature of the material being operated upon, whether hard and cross-grained, or soft, silky, and straight-grained, the angles being increased for the first and diminished for the last. The ground and sharpened angles of a trying-plane iron suitable for soft wood and hard wood alike, though not adapted for very hard and crooked curly grain- Of course the sharpening angle will be constantly changing, being first but slightly greater than the grinding angle but gradually thickening with each re-sharpening, until the facet becomes almost or quite coincident with the face of the material, at which stage re-grinding becomes necessary. The position of the top iron should properly vary with different classes of material. The harder the wood, the greater tendency there is to chatter and choke, with the consequent production of a roughened and wavy surface ; and the top iron should there-fore be brought very close to the cutting edge, so that in certain cases the edge of the cutting-iron (A) will project only as a fine line beyond the top iron. In soft woods, on the contrary, the best results are obtained by keeping the top iron farther back, say to the extent of full if the wood is wet, a distance quite unsuited to hard curly stuff.
Angles for grinding and sharpening
The top iron placed at a medium distance back, adapted for ordinary working of dry pine and deal, or straight-grained hard wood. The proper bedding of the iron on its seat, and its even wedging, have much influence in preventing choking of the shaving. If the iron rocks upon its seat, though only in a very slight degree, or if the wedge does not exert an equal pressure all over alike, choking will certainly occur, and these points must therefore be looked to if the plane is found to work unsatisfactorily; they are easily remedied by removing the higher points of contact of the wood, with a chisel in the case of the seating, and with a plane when the wedge is tight. The wedge should never be tight sideways, since, if then driven in hard, it is apt to split out the wood of the stock close beside the iron. A very slight correction of the bedding of the iron and the fitting of the wedge will often work marvels. The width of the mouth ought not to be greater than will permit of the free passage of the shavings upwards, not-withstanding that, in consequence of the wearing of the face, it becomes unavoidably increased. A moderate in-crease in width, say up to bin., will not materially interfere with the proper working of the plane ; but anything exceeding that amount interferes with the proper planing of short pieces of stuff, causing a slight digging inwards of the iron to occur just at the commencement of removing a shaving. Then the usual practice is to reduce the mouth to its original width, by fitting in a dovetailed slip of wood in front of the cutting-edge of the iron. Some even glue a fresh sole, on the face of the plane, throughout its whole length, thus narrowing the mouth, and at the same time restoring the plane to its original depth and weight, both being points of value, a heavy bench plane always working better than a light one. The widening of the mouth is partly affected by the fact that all common plane-irons taper backwards, being thinner at the top end than next the cutting-edge ; the iron, therefore, as it becomes worn back, leaves the mouth more open in consequence.