Figure 4-45.-Ellipse by four-center method.ELLIPSE BY FOUR-CENTER METHODThe four-center method is used for smallellipses. Given major axis, AB, and minor axis,CD, mutually perpendicular at their midpoint, O,as shown in figure 4-45, draw AD, connecting theend points of the two axes. With the dividers setto DO, measure DO along AO and reset thedividers on the remaining distance to O. With thedifference of semiaxes thus set on the dividers,mark off DE equal to AO minus DO. Drawperpendicular bisector AE, and extend it tointersect the major axis at K and the minor axisextended at H. With the dividers, mark off OMequal to OK, and OL equal to OH. With H asa center and radius R1 equal to HD, draw thebottom arc. With L as a center and the sameradius as R1, draw the top arc. With M as a centerand the radius R2 equal to MB draw the end arc.With K as a center and the same radius, R2, drawthe end arc. The four circular arcs thus drawnmeet, in common points of tangency, P, at theends of their radii in their lines of centers.ELLIPSE BY CONCENTRIC-CIRCLE METHODFigure 4-46 shows the concentric-circle methodof drawing an ellipse. With the point of inter-section between the axes as a center, draw twoconcentric circles (circles with a common center),one with a diameter equal to the major axis andthe other with a diameter equal to the minor axis,as shown in figure 4-46, view A. Draw a numberof diameters as shown in figure 4-46, view B.From the point of intersection of each diameterwith the larger circle, draw a vertical line; andfrom the point of intersection of each diameterwith the smaller circle, draw an intersectinghorizontal line, as shown in figure 4-46, view C.Draw the ellipse through the points of inter-section, as shown in figure 4-46, view D, with afrench curve.Figure 4-46.-Ellipse by concentric-circle method.4-16
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
