All the planes hitherto considered, whether used parallel with the surfaces, as in straight works, or as tangents to the cur\ as in curved works, are applied under precisely the same circumstances, as regards the angular relation of the mouth, because the edge of the blade is a right line parallel with the sole of the plane; but when the outline of the blade is curved, some new conditions arise which interfere with the perfect action of the instrument. It is now proposed to examine these conditions in respect to the semicircle, from which the generality of mouldings may be considered to be derived.

In the astragal, a, b, c, d, e, fig. 844, a small central portion at c, may be considered to be a horizontal line; two other small portions at b, and d, may be considered as parts of the vertical dotted lines, b,f, and d, g; and the intermediate parts of the semicircle are seen to merge from the horizontal to the vertical line.

The reason why one moulding plane figured to the astragal cannot, under the usual construction, be made to work the ver-tieal parts of the moulding with the same perfection as the horizontal, consists in the fact, that whereas the ordinary plane iron-presents an angle of some 45 to 60 degrees to the sole of the plane, which part is meant to cut, it presents a right angle to the side of the plane, which part is not meant to cut. Thus the parts of the iron of the square rebate plane, which protrude through the sides of the stock, were sharpened ever so keenly, they would only scrape and not cut, just the same as the scraping plane with a perpendicular iron.

When, however, the rebate plane is meant to cut at the side, it is called the side-rebate plane, and its construction is then just reversed, as shown in the three views, fig. 346; that is, the iron is inserted perpendicularly to the sole of the plane, but at a horizontal angle x x, or obliquely to the side of the plane, so that the cut is now only on the one side z z, of the plane, and which side virtually becomes the sole. A second plane sloped the opposite way, is required for the opposite side, or the planes are made in pairs, and are used for the sides of grooves, and places inaccessible to the ordinary rebate plane.

Section III Moulding Planes 20020

In the figures 344 and 345, the square rebate planes 1 and 2, will cut the horizontal surfaces a, b, and c, perfectly, because the irons present the proper slopes to these surfaces; but in attempting to plane the vertical line b f, with the side of 1, we should fail, because the cutter is at right angles to that superficies, and it would only scrape, or be said to drag. The plane 3, when laid on its side, would act perfectly on the vertical face, but now it would be ineffective as regards the horizontal. The square rebate plane, if applied all around the semicircle, would be everywhere effective so long as its shaft stood as a radius to the curve, in fact as at 2, and 3, as then the angle of the iron would be in the right direction in each of its temporary situations. But in this mode a plane to be effective throughout, demands either numerous positions of the plane, or an iron of such a kind as to combine these several position

Theoretically speaking therefore, the face of the cutter suitable to working the entire semicircle or bead, would become cone, or like a tube of steel bored with a hole of the same diameter the bead, turned at one end externally like a cone, and split in two parts. Fig. 847 would represent such a cutter, and which just resembles a half round gouge applied horizontally and sharpened externally. But this theoretical cutter would present all the difficulties of the spokeshave iron; as to the trouble of fixing it, its interference with the sole of the plane, and the diffi-culty of maintaining the form of the mouth of the instrument, if made as a spokeshave, owing to the reduction of the cutter in sharpening.*

But as the iron 3, and also the side-rebate, fig. 346, work perfectly well in their respective positions, or when the cutters are inclined horizontally, whilst the central iron 2, only requires to be inclined vertically, it occurred to me that by employing a cutter in all respects as usual, except that its face should be curved as in the arc connecting the three irons in fig. 345, the one tool would cut equally well at every point of the curve; and experience proved the truth of the supposition. The precise form of the iron will be readily arrived at, by cutting out in card the diagram, fig. 348, and bending it to a circular sweep, until the parts exterior to the dotted lines bf, - d g, just meet the spring of the bead, at about the angle of half or middle pitch, or 30 or 35 degrees from the right angle, and it will be then found necessary to cut away the corners to the lines b s, - d s, or so much of them as dip below the straight surface of the fillet, as seen in fig. 349.

The author had a plane constructed exactly in agreement with the above particulars, that is, with an iron curved to about the third of a circle, the mouth of the plane was curved to correspond, and in every other respect the instrument was as usual; it was found entirely successful.

The inclination of the tool to each part of the work is very

* The cutter 347, is used fur making the cylindrical rollers upon which ribbons are wound; the cutter is fixed at the end of * slide, and is worked by a lev the cylinders are made at two cuts in lengths of 8 or 10 inches, and afterwards nearly alike, and it assimilates at different parts to each of the ordinary rebate planes, all of which work well. Namely, at the crown of the moulding c, to the square rebate plane; at the spring b and d, to the side rebate planes; and at the fillets a b, d e, to the skew rebate. And notwithstanding the fluted form of the iron, no greater difficulty is experienced in sharpening the iron in the new form like a gouge, than in the old like a chisel, the figure of the end being nearly alike in each case.*