Chalk-Lining (). Lay off points on lines ab and ad 1/2" apart, the first point in each case being 1/4" from the working-face. Through the points thus located, chalk-lines are to be made, as shown by face A, Fig. 137.

Insert the awl at the first point on the line ab, and drawing the cord tight with one hand, apply the chalk with the other, beginning at the awl. Care must be taken that the cake of chalk is not cut to pieces by the cord. A little practice will make it easy to hold the cord under the thumb in such a way as to form a small shoulder on the chalk, Fig. 139, which by the friction of the cord will be gradually carried across the face of the cake; another is then formed to take its place. When the cord has been chalked, stretch it over the point on the line ad that corresponds to the point on the line ab at which the awl is inserted. Then raise the cord near the middle as shown by Fig. 140, and by suddenly releasing it, cause it to "snap" on the surface of the work. In snapping, the cord should be drawn up vertically, for if drawn at an inclination as shown by a, Fig. 141, a wide blurred line will be produced. Repeat this operation for each of the points, finishing face A as shown. Each line should be clear and well-defined. Try to make each one better than the preceding. Never snap more than once between the same points.

Fig. 139

Fig. 140

Operations to be performed on Face B, from A as a Working-Face, Fig. 137.