Make the angle o c t (Fig. 177) equal to the angle o c t at Fig. 144; upon c describe a circle with a radius equal to half the thickness of the rail; draw the tangent b d parallel to t c, and complete the rectangle e b d f, having sides tangical to the circle; from c draw c a at right angles to o c; then, b d being the bottom of the rail, set a gauge from b to a, and run it the whole length of the stuff; in boring, place the centre of the bit in the gauge-mark at a, and bore in the direction a c. To do this easily, make chucks as represented in the figure, the bottom edge, g h, being parallel to o c, and having a place sawed out, as e f, to receive the rail. These being nailed to the bench, the rail will be held steadily in its proper place for boring vertically. The distance apart that the balusters require to be, on the under-side of the rail, is one half the length of the rake-side of the pitch-board.