Construction of Arc Tangent to Perpendicular Lines
Drawing a fillet or round comprises the problem of drawing a circular arc of a given radius tangent to two nonparallel lines. Figure 4-33 shows a method that can be used when the two nonparallel lines form a right angle. AB is the given radius of the arc. Set a compass to this radius, and, with the point of intersection of the lines as a center, strike an arc intersecting the lines at C and D. With C and D as centers and the same radius, strike intersecting arcs as shown. The point of intersection of these arcs (0) is the center of the circle of which an arc of the given radius is tangent to the lines.