information is given. The seat of the plane-iron is made at different angles, to give the pitch to suit different kinds of work. The four angles most in use are as follows:—Common pitch, in which the seat for the back of the iron is at an angle of 45° from the sole (this inclination is usually employed for all planes for soft wood); York pitch, which has an angle of 50°, and is adapted for use with mahogany and other hard, stringy woods; middle pitch or 55°, and half pitch or 60°, which are employed with moulding planes, the former being for soft wood and the latter for the harder kinds.
Fig. 190 affords an idea of three angles, A giving the set of a half-pitched plane, B that of an ordinary plane, while C shows the inclination of an extra-pitched plane. The pitch or angle at which the cutter is set is of importance. There are three angles involved in this case: (1) The angle between the cutter and the surface of the work; this should be as small an angle as possible. It is obvious that if the surfaces of the cutter and the work were perfectly parallel, the cutter would glide over the surface without cutting, except under great pressure. By making the cutter edge rather than its whole surface touch the work, the tendency to cut and to continue the contact is secured. The angle, which may be called the clearance angle, or the back angle, should only be enough to secure this condition of contact. (2) The angle of the cutter itself. The more acute this angle the better, if only the material will stand the strain and face the work without losing its edge. (3) The front or remaining angle may be found by subtracting both (1) and (2) from 180°, if dealing with plane surfaces, and is available for the passing away of the waste material; in the case of the plane, however, this is limited, in order to provide means to prevent the shaving being torn up in advance of the cutting action. This provision is made by the front portion of the plane, and to be efficacious must be in contact with the work and as near the edge of the cutter as possible to allow waste to escape. A few experiments with a knife will show that for soft materials a slight angle is best. This involves a thin knife, and its side almost in contact with the material to be cut; but as harder things are tried the stiffness of the cutter, and the consequent angle, must be increased, not because it is merely desirable, but because it is absolutely necessary to have a stronger cutter. The more upright an iron is set, the less liable is it to tear up the wood in planing; but in the same degree the iron loses its edge more quickly, is more likely to jump and chatter, and is more laborious to work. In toothing planes the irons are set upright, and in “old woman’s tooth planes” or routers nearly upright. In working with an upright iron, the action of the tool is that of scraping the work, while the more the iron is inclined the nearer it approaches the action of splitting the wood. For this reason an ordinary or extra-pitched plane is more liable to splinter up the surface of a piece of work; but this accident may be in great measure prevented by using a properly adjusted back iron. Moulding planes, rounds and hollows, bead planes, and others that work without a back-iron, are usually preferred set to the half-pitch angle; while for working on end-grained stuff, extra-pitched tools, such as shoulder and bull-nosed planes, give the best results. In examining the side of a plane-iron, it is found to be made up of an iron back faced with steel. The steel, welded on to the iron and distinguished by its brighter colour and finer grain, acts as a cutting edge, the iron being required to give sufficient stiffness to prevent chattering. When newly ground and sharpened, a plane-iron has three angles, one due to the pitch, A (
Fig. 191), one made by the grindstone, B, and one made by the oilstone, C. The angles A and B do not alter, but C gradually becomes more acute with sharpening on the oilstone, until it lines with the face of the plane, as in
Fig. 192, when the iron refuses to cut properly, and requires grinding. The pitch angle A (
Fig. 190) varies in planes by different makers, as described above.
Fig. 190.—Three Pitch Angles for Planes.
Fig. 191.—The Three Angles of a Plane Iron.
Fig. 192.—Plane Iron before and after Grinding.
GRINDING PLANE CUTTING IRONS.
As stated above, when a plane-iron has been sharpened on the oilstone a number of times the edge becomes thick as in Fig. 192, when the portion shown black in the drawing should be removed by the grind-stone. Of course it might be taken off with the oilstone, but this would involve a waste of time, the more economical plan being to keep the oilstone simply for imparting a keen edge, and using the grind-stone to take off the waste material at the back as occasion requires. The iron may be ground as follows: The worker should stand, if possible, with the grindstone revolving towards him. The stone should be well wetted, as a dry grindstone will heat the tool and spoil its temper. The back iron may be kept on the plane cutter and set about 1/8 in. back. This allows of a firmer grip being taken of the iron, and forms a gauge for keeping the cutting edge square, if it should be required. Fig. 193 shows the method of holding the tool on the stone; it should first be held towards the top, and the iron gradually lowered towards the worker until the bevel of the iron fits the stone, which may be felt by the additional force required to keep the tool in position. The grinding should be stopped just before the cutting edge is reached, unless it is required to remove a gap. or the iron is out of square. Some grind the iron until there is a wire edge 1/16 in. long attached to the cutting edge, and as this has to be removed with the oilstone, that much of the iron is wasted, leaving the tool at the finish exactly the same as if the grinding had been stopped just before it reached the edge. The iron should not be ground too thin, or it will chatter. On the other hand, if too thick, it will soon require grinding again. If the angle is made about three times as long as the iron is thick, it will give a good working result. A mechanical appliance for maintaining the plane iron at a certain angle on the grindstone is illustrated by Fig. 194, which is self-explanatory.
Fig. 193.—Grinding Plane Iron.
Fig. 194.—Tool-grinding Rest.
SHARPENING PLANE CUTTING IRONS ON THE OILSTONE.
A good oilstone, capable of putting a keen edge on the tool, is a necessity to all woodworkers. Washita, Nova Scotia, and other fast cutting stones are useful for removing waste metal when the iron is thick; but it is seldom that one of these stones can be trusted to leave a keen edge on the tool. Turkey stones are the only stones that have the two good qualities combined of cutting quickly and leaving a good edge. Charnley Forest oilstones are slow cutters, but they are to be relied on for leaving a good keen edge. It is necessary that the oilstone should be kept perfectly level, or it will not be possible to get a true edge. The stone should also be free from grit, or the iron will be gapped in sharpening, and will leave ridges on the planed work. (Fuller particulars of the varieties of oilstones will be given later.) In sharpening the iron after it has been newly ground, the hands should be kept low to make the bevel correspond nearly with that made by the grindstone. As time goes on, when the iron is resharpened the hands are kept a little higher upon each occasion (see Fig. 195), until it becomes thick, as in Fig. 192, then it must be again put upon the grindstone. Some workers find it convenient to use two
