Figure 5-37.-Isometric projection of a cube.that the figure has a central axis, formed by thelines OA, OB, and OC. The existence of this axisis the origin of the term axonometric projection.In an isometric projection, each line in the axisforms a 120-degree angle with the adjacent line,as shown. A quick way to draw the axis is to drawthe perpendicular OC, then use a T square and30°/60° triangle to draw OA and OB at 30 degreesto the horizontal. Since the projections of parallellines are parallel, the projections of the otheredges of the cube will be, respectively, parallel tothese axes.A rectangular object can be easily drawn inisometric by the procedure known as boxconstruction. In the upperpart of figure 5-39,there is a two-view normal multi-view projectionof a rectangular block. An isometric drawing ofthe block is shown below. You can see how youbuild the figure on the isometric axis and how youlay out the dimensions of the object on theFigure 5-38.-Use of an isometric axis.isometric drawing. Because you lay out theidentical dimensions, it is an isometric drawingrather than an isometric projection.Non-isometric Lines.— If you examine theisometric drawing shown in figure 5-39, you willnote that each line in the drawing is parallel toone or another of the legs of the isometric axis.You will also notice that each line is a normal linein the multi-view projection. Recall that anormal line is a line that, in a normal multi-viewprojection, is parallel to two of the planes ofprojection and perpendicular to the third. Thus,Figure 5-39.-Use of “box construction” in isometricdrawing.5-21