Technical Drawing and Sketching, ContinuedSketching arcs,Sketching arcs, circles, and ellipses are very similar processes. Lightlycircles, andellipsesdrawing a box to the proportion of the desired arc, circle, or ellipse will helpin its construction. Using combined movements of your wrist and fingers,make short counterclockwise strokes. When you must join arcs to straightlines, draw the straight lines first to locate the ends of the arcs.Figure 4-6 illustrates the sketching of arcs and circles within a box.Figure 4-6.—Sketching arcsand circles.You may also draw circles and ellipses using a trammel. A trammel is alength of cardboard or paper marked with both the major and minor axis ofthe desired ellipse. Place the trammel so that two of the points are on therespective axes. Mark the third point clearly since this point will form thecurve on the paper. Place a dot periodically at the third point as you movethe other two points along the axes. Place enough points to ensure a smoothand symmetrical ellipse. Sketch the ellipse lightly, then follow more heavilywith the aid of irregular curves.Figure 4-7 shows the use of a trammel.Figure 4-7.—Using a trammel to form acircle.Continued on next page4-8
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