A recent improvement in jack-, smooth-, and fore-planes consists of an adjustable frog, by means of which the throat can be narrowed or widened at will by means of a set-screw in the rear of the frog without removing the clamp and cutter. It is made by Sargent and Company. The Stanley "Bed Rock" plane has a similar but less convenient device.
The splitting of the wood in advance of the edge is also prevented by the breaking of the shaving as it hits against the cutter or its cap. Hence the advantage of bending up and breaking or partly breaking the shaving as soon as possible after it is cut. This shows why the cap is set close to the edge of the cutter. Another reason is that it thereby stiffens the cutter and prevents "chattering." If a thick shaving be desired the cap has to be set farther back. In a smooth-plane 1⁄32 inch is enough, in a jack-plane ⅛ inch is often desirable. The following are the planes in common use:
The jack-plane, Fig. 102, 14" to 15" long, is the one used where a considerable amount of material is to be taken off to bring a piece of wood to size, and therefore the outline of the cutting edge instead of being straight is slightly curved or "crowned" so that in planing the surface of a board it makes a series of shallow grooves, the ridges of which must afterward be smoothed off by another plane. Also for beginners whose hands are not strong it is sometimes wise to grind the cutter with some "crown", in order to take off narrow shavings, which require less strength. For school use, where the jack-plane is used for all purposes, the cutter is usually ground almost straight and only the corners rounded as in the smooth-plane and the fore-plane.5
Footnote 5: In whetting a plane-bit, a slight crown may be given it by rubbing a bit harder at the ends of the edge than in the middle. Strop in the same way as a chisel ([p. 59]).
Fig. 102. Sighting Along the Sole of Jack-Plane.
The fore-plane, 22" to 26" long, and the jointer, 28" to 30" long, are large planes, similar to the jack-plane, except that the cutting edge is straight. They are used for straightening and smoothing long pieces.
The smooth-plane, 5½" to 10" long, is a short plane, similar to the jack-plane, except that the cutting edge is straight. It is used for smoothing.
These four planes, the jack-plane, the fore-plane, the jointer, and the smooth-plane, are essentially alike, and directions for the use of one apply to all.
There are two chief adjustments in the Bailey iron plane: the brass set-screw, see 8 in Fig. 101, which regulates the depth of the cut, and the lever, 9, which moves the cutter sidewise so that it may be made to cut evenly. The skilful worker keeps constant watch of these adjustments. It is well to form the habit of always sighting along the sole before beginning to plane, in order to see that the cutter projects properly, Fig. 102. It is a common mistake among beginners to let the cutter project too far.