Fig. 23. Irons of Smooth and Jack Planes
10. The Jack Plane. The ordinary plane iron has a straight edge, as shown at a, [Fig. 23], but when a large quantity of wood is to be removed the iron is sharpened in the shape shown at b. This curved iron will cut out the wood in hollows, leaving ridges between, and it is necessary to follow this jack plane with a finer one having a straight edge in order to smooth the surface. The jack plane might be called a roughing plane.
Fig. 24. Relative Sizes of Smooth and Jack Planes
The lower figure is a jack plane
11. The Smooth Plane. The smoothing plane is shorter than the jack plane, its object being to smooth the surface without regard to straightening it, as it is supposed that the straightening has previously been done. The cap iron in the smooth plane should be set from a sixteenth to a thirty-second of an inch from the cutting edge of the plane iron.
Fig. 25. Action of Short and Long Planes
12. Jointers. For straightening very rough and uneven stock a long plane is necessary ([Fig. 25]). In the illustration let line ab represent the edge of a very uneven board. A short plane c would simply follow the hills and hollows, smoothing but not straightening it, while a long plane, as shown at d, would merely cut off the top of the high places, as shown by the dotted line, and would not touch the bottoms of the hollows until all the elevations were leveled; in other words, until the surface was straightened. Such planes, which are often three feet long or more, are called jointers.