Fig. 319.

Thus, although convex surfaces, such as the outside of a hoop, may be wrought by any of the straight planes, applied in the direction of a tangent as at a, it is obvious the concave plane, b, would be more convenient. For the inside of the hoop, the radius of curvature of the plane must not exceed the radius of the work: thus c, the compass plane, would exactly suit the curve, and it might be used for larger diameters, although in a less perfect manner. For the convenience of applying planes to very small circles, some are made very narrow or short, and with transverse handles such as d, the plane for the hand-rails of staircases, the radius of its curvature being three inches; it resembles the spokeshave e, as respects the transverse handles, although the hand-rail plane has an iron, wedge, and stop, much like those of other planes.

The sections of planes, are also either straight, concave, convex, or mixed lines, and suited to all kinds of specific mouldings, but we have principally to consider their more common features, namely, the circumstances of their edges and guides; first, of those used for flat surfaces, called by the joiners, bench planes; secondly, the grooving planes; and thirdly, the moulding planes.

The various surfacing planes are nearly alike, as regards the arrangement of the iron, the principal differences being in their magnitudes. Thus the maximum width is determined by the mirage strength of the individual, and the difficulty of maintaining with accuracy the rectilinear edge. In the ordinary bench planes the width of the iron ranges from about 2 to 2 1/2 inches.*

The lengths of planes are principally determined by the degree of straightness that is required in the work, and which may be thus explained. The joiner's plane is always either balanced upon one point beneath its sole, or it rests upon two points at the same time, and acts by cropping off these two points, without descending to the hollow intermediate between them. It is therefore clear, that by supposing the work to be full of small undulations, the spokeshave, which is essentially a very short plane, would descend into all the hollows whose lengths were greater than that of the plane, and the instrument is therefore commonly used for curved lines. But the greater the length of the plane, the more nearly would its position assimilate to the general line of the work, and it would successively obliterate the minor errors or undulations; and provided the instrument were itself rectilinear, it would soon impart that character to the edge or superficies submitted to its action. The following table may be considered to contain the ordinary measures of surfacing planes.

 Names of Planes. Lengths, in inches. Widths, in inches. Widths, of Irons. Modelling Planes, like Smoothing Planes... . 1 to 5 - 1/4 to 2 - 2/16 to 1 1/2 Ordinary Smoothing Planes........ 6 1/2 to 8 - 2| to 3 1/8 - 1 3/4 to 2 3/8 Rebate Planes........... 9 1/2 - 3/8 to 2 - 3/8 to 2 Jack Planes............... 12 to 17 - 2 1/2 to 3 - 2 to 2 1/4 Panel Planes............. 14 1/2 - 34 - 2 1/2 Trying Planes............. 20 to 22 - 3 1/4 to 3 3/8 - 2 3/8 to 2 1/2 Long Planes............ 24 to 26 - 3 5/8 - 2 5/8 Jointer Planes......... 28 to 30 - 3 3/4 - 2 3/4 Cooper's Jointer Planes.... 60 to 72 - 5 to 5 1/4 - 3 1/2 to 3 3/4

The succession in which they are generally used, is the jack plane for the coarser work, the trying plane for finer work and trying its accuracy, and the smoothing plane for finishing.

* The " iron" is scarcely a proper name for the plane-iron, which is a cutter or blade, composed partly of iron and steel; but no confusion can arise from the indiscriminate use of any of these terms.

The diagram, fig. 320, is one quarter the full site, and may be considered to represent the ordinary surfacing planes, the mouths of which are alike, generally about one-third from the front of the plaine, and thus constituted. The line a, b, is called the sole; c,d, upon which the blade is supported, is the bed, and this, in planes of common pitch, is usually at an angle of 45° with the perpendicular.

Fig. 320.

The mouth of the plane is the narrow aperture between the face of the iron, and the line c,f, which latter is railed the the angle between these should he as small as possible, in order that the wearing away of the sole, or its occasional correction, may cause hut little enlargement of the mouth of the plane; at the same time the angle must be sufficient to allow free egress for the shavings, otherwise the plane is said to choke. The line g. is called the front, its angle is unimportant, and in practice it is usually set out one quarter of an inch wider on the upper surface than the width of the iron.

The wedge of the plane which fixes the iron is commonly at an angle of 10°, and it is slightly driven between the face of the iron and the shoulder or abutment, c, e. It is shown by the two detached views, that the wedge w, is cutaway at the central part, both to clear the screw which connects the double iron, and to allow room for the escape of the shavings. The wedge is loosened by a moderate blow, either on the end of the plane at h, on the top at i, or by tapping the side of the wedge, which may be then pulled out with the fingers; a blow on the front of the plane at j, sets the iron forward or deeper, but it is not resorted to.

In all the bench planes, the iron is somewhat narrower than the stock, and the mouth is a wedge-formed cavity; in some of the narrow planes the Cutting edge of the iron extends the full width of the sole, as in the rebate plane f, fig. 319, page 475; in these and others, the narrow shaft of the iron and the thin wedge alone proceed through the stock, and there is a curvilinear mouth extending through the plane; the mouth is taper, to turn the shavings out on the more convenient side. When the planes only cut on the one part of the sole, as in fig. 332, page 4S5, the angular mouth extends only part way through the plane, and the curvilinear perforation is uncalled for.

In the diagram, fig. 320, when the stock terminates at the dotted line, s, s, it represents the smoothing plane; when it is of the full length, and furnished with the handle or toat, it is the jack plane or panel plane; the still longer planes have the toat further removed from the iron, and it is then of the form shown in fig. 330, page 483.