lines, as a, b, c, etc.; and from these lines draw horizontal lines d, e, f, etc. Now divide the lower half of circle D into twice as many equal divisions as quarter circle K is divided into, and from these points of division draw perpendiculars g, h, i, etc. And where these perpendiculars cross the horizontal lines, as d, will be points through which the curve may be drawn, three of such points being marked by dots at p, q, 1.

If the student will, after having drawn the curve by this construction, draw it by the construction that was explained in connection with Figure 79, he will find the two methods give so nearly identical curves, that the latter and more simple method may be used without sensible error.

When the curves of the moulding are not arcs of circles they may be marked as follows:

Take the drawing of the moulding and divide each member or step of it by equidistant lines, as a, b, c, d, e, f, g, in Figure 294; above the moulding draw lines. representing the cutter, and having found the depth of cutting edge for each member by the construction shown in Figure 292, finding a separate line, a b, for each member of the moulding, transfer the depths so found to the face of the cutter; divide the depth of each member of the cutter into as many equal divisions as the corresponding member of the moulding is divided into, as by lines h, i, j, k, l, m, n. Then draw vertical lines, as o, p, q, r, etc.; and where these lines meet the respective lines h, i, j, etc., are points in the curve, such points being marked on the cutter by dots.

CHAPTER XIII.

EXAMPLES IN LINE-SHADING AND DRAWINGS FOR LINE-SHADED ENGRAVINGS.

ALTHOUGH in workshop drawings, line-shading is rarely employed, yet where a design rather than the particular details of construction is to be shown, lineshading is a valuable accessory. Figure 295, for example, is intended to show an arrangement of idle pulleys to guide belts from one pulley to another: the principle being that so long as the belt passes to a pulley moving in line with the line of rotation of the pulley, the belt will run correctly, although it may leave the pulley at considerable angle. When a belt envelops two pulleys that are at a right angle to each other, two guide pulleys are needed in order that the belt may, in passing to each pulley, move in the same plane as the pulley rotates in, and the belt is in this case given what is termed a quarter twist.

It will be observed that by the line-shading even the twist of the belt is much more clearly shown than it would be if left unshaded.

An excellent example of shading is given in Figure 296, which is extracted from the American Machinist, and represents a cutting tool for a planing machine. The figure is from a wood engraving, but the effect may be produced by lines, the black parts being considered as simply broad black lines.