point. It follows that one method of drawing aline tangent to a circle at a given point is to drawthe radius that intersects the point, and then drawthe line tangent at the point of intersection andperpendicular to the radius.Another method is shown in figure 4-32. Todraw a line tangent to the circle at P, set acompass to the radius of the circle, and, with Pas a center, strike an arc that intersects the circleat A. With the compass still set to the radius ofthe circle, use A as a center and strike an arc thatintersects the first arc at B. With B as a centerand the compass still set to the radius of thecircle, strike another arc. A line through the pointof intersection (0) of the last drawn arc andthrough P is tangent to the circle at P.CIRCULAR ARC OF AGIVEN RADIUS TANGENTTO TWO STRAIGHT LINESDrawing a fillet or round comprises theproblem of drawing a circular arc of a given radiustangent to two nonparallel lines.Figure 4-33 shows a method that can be usedwhen the two nonparallel lines form a right angle.AB is the given radius of the arc. Set a compassto this radius, and, with the point of intersectionof the lines as a center, strike an arc intersectingthe lines at C and D. With C and D as centersand the same radius, strike intersecting arcs asFigure 4-32.-Line tangent to a given point on a circle.Figure 4-33.-Circular arc tangent to two lines that forma right angle.shown. The point of intersection of these arcs (0)is the center of the circle of which an arc of thegiven radius is tangent to the lines.Figure 4-34 shows a method that can be usedregardless of the size of the angle formed by thelines. Again AB equals the given radius of the arc,and the problem is to draw an arc with radiusequal to AB, tangent to CD and EF. Draw GHparallel to CD and at a distance from CD equalto the given radius of the arc. Draw IJ parallelto EF and also at a distance equal to the givenradius of the arc. The point of intersectionbetween GH and IJ (P) is the center of the circleof which an arc of the given radius is tangent toCD and EF.Figure 4-34.-Circular arc tangent to two lines that formany angle.4-11

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