The modern iron plane, illustrated in Fig. 21, can now be bought in a great variety of sizes and styles. These planes, with their true and unchanging faces, and their simple appliances for setting and adjusting the cutter, or plane iron, to the face of the plane and to the required thickness of shavings, are greatly to be preferred to the old-style wooden planes. Construction. The general construction of the iron plane will be readily understood from Fig. 22, one side of the plane being removed to show the arrangement of the parts. The cutter, or plane iron a is made of the best cast steel, and is of equal thickness throughout; in all new planes this part will be found ground and sharpened for immediate use. The cap iron f, Fig. 22, is fastened to the plane iron by an adjusting screw, as shown in Fig. 23. For whetting or grinding the cutting edge, it is not necessary to remove the cap iron, but only to loosen the connecting screw and to slide the cap back to the extreme end of the slot in the plane iron, tightening it there by a turn of the screw. The cap iron will then serve as a convenient handle or rest for the workman in whetting or grinding the blade.
Fig. 20. Compass Saw Teeth.
Fig. 21. Iron Plane.
The iron lever c, Fig. 22, is held in place below its center by the screw g, which acts as a fulcrum, and the lever is readily clamped down upon the irons by the use of the cam piece d. When this cam is turned upward it ceases to bear upon the irons, and the lever c may then be removed from its place, and the irons released, without turning or changing the adjustment of the screw g, as the lever and irons are properly slotted for this purpose. Should the pressure required for the best working of the plane iron need changing, it can easily be obtained by tightening or loosening the screw g.
When the plane iron is secured in its place, the use of the brass thumb screw ft will draw or drive the plane iron, and thus the thickness of the shaving to be taken from the work can be regulated with perfect accuracy. By the use of the lever e, located under the plane iron and working sidewise, the cutting edge can easily be brought into position exactly parallel with the face of the plane, should any variation exist when the iron is clamped down. To ascertain this, hold the plane up, and look down over its face; the greater projection, if there is any, of one or the other of the corners of the iron, can readily be seen.
Fig. 23. Plane Iron - Cap Iron Connection.
The cap iron f, which is not sharp, is not used for the purpose of strengthening or stiffening the cutting iron, as is often supposed, but as a chip break to prevent the cutting edge of the plane iron from chipping, tearing, and breaking the grain of the wood below the surface when the grain turns and twists, or when it is knotty and crooked. In such cases the tendency of the plane iron is to split and tear out the fibers of the wood in front of the cutting edge. To avoid this, the cap iron is screwed on, with its dull edge quite close to the cutting edge, so as to bend and break off the fibers or the shavings before the split gets fairly started below the surface.
The cutting edge of the plane iron is said to have lead in proportion to the distance it is placed in advance of the dull edge of the cap iron. The depth of the splits, or the roughness of the cross-grained surface, will be just equal to the lead of the cutting edge. For soft straight-grained wood the lead may be 1/32 inch or even more, but this must be reduced in proportion as the wood is curly, cross-grained, or knotty.
The grinding, or the whetting, must always be done on the bevel side only of the plane iron, the upper side being kept as flat and as smooth as possible to secure easy working.
All plane irons should be ground slightly rounding to the extent of the thickness of a thin shaving. This rounding of the cutting edge should be the true arc of a circle throughout the entire length of the cutting edge, and not simply a rounding-off of the corners as is sometimes directed. Rounding the edge to the extent of the thickness of a shaving prevents the plane iron from grooving into, or plowing out a wide groove in the surface that is being worked, and also assists greatly in working the edges of the piece to right angles, or square with the face side. To do this, it is not necessary, should one corner of the edge be higher than the other, to tilt the plane on the high edge, but, while holding it flat and firm on the surface of the edge being planed, the plane should be pushed sidewise toward the highest corner in order to reduce that corner. This is readily understood when we remember that the cutting edge of the iron is rounding. If the plane is held so that the middle of the plane iron does the cutting, the shaving planed is of the same thickness on both edges; but if the plane is pushed over to one side, either to the right or to the left, the shaving will be featheredged, or thick on one edge and thin on the other, thus reducing the higher corner of the edge of the piece.
When the plane is to be used, the beginner should first carefully adjust it to the thickness of shaving required by moving the adjusting screw in the proper direction, at the same time holding it up and looking down over the face of the plane, when the projection of the plane iron can readily be seen. The cut should also be tested by trying it on the piece to be planed until the plane is ready for use.
The operator's position should be one of perfect ease, standing well back of the piece to be planed, and pushing the plane to arm's length from, not alongside of, the operator, taking long and continued shavings from the board. When starting the shaving at the end of the board, care should be taken to hold the forward end of the plane down firmly, or the act of pushing it forward will cause that end to tilt up and the plane iron to chatter on the surface as it begins to cut the shaving. This is due to the fact that nearly two-thirds of the plane overhangs the end of the board, requiring firm pressure on the forward end to balance it while the stroke is being started.
To insure smooth work, care must be taken to plane with the grain of the wood, and not against the ends of the fibers as they lie in the surface of the board. Should the fibers tear out and the surface become rough, reverse the ends of the boards so as to cut the shaving in the opposite direction, and note the difference in the effect on the planed surface.