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Axonometric Projection
Drawing  an  angle  in  isometric

Engineering Aid 3 - Beginning Structural engineering guide book
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Figure 5-37.-Isometric projection of a cube. that the figure has a central axis, formed by the lines OA, OB, and OC. The existence of this axis is the origin of the term  axonometric   projection. In  an  isometric  projection,  each  line  in  the  axis forms a 120-degree angle with the adjacent line, as shown. A quick way to draw the axis is to draw the perpendicular OC, then use a T square and 30°/60° triangle to draw OA and OB at 30 degrees to the horizontal. Since the projections of parallel lines  are  parallel,  the  projections  of  the  other edges of the cube will be, respectively, parallel to these  axes. A  rectangular  object  can  be  easily  drawn  in isometric   by   the   procedure   known   as   box construction.  In  the  upperpart  of  figure  5-39, there is a two-view normal multi-view projection of  a  rectangular  block.  An  isometric  drawing  of the  block  is  shown  below.  You  can  see  how  you build the figure on the isometric axis and how you lay  out  the  dimensions  of  the  object  on  the Figure 5-38.-Use of an isometric axis. isometric   drawing.    Because  you  lay  out  the identical  dimensions,  it  is  an  isometric  drawing rather  than  an  isometric  projection. Non-isometric  Lines.—  If you examine the isometric drawing shown in figure 5-39, you will note that each line in the drawing is parallel to one or another of the legs of the isometric axis. You will also notice that each line is a normal line in   the   multi-view   projection.   Recall   that   a normal line is a line that, in a normal multi-view projection,  is  parallel  to  two  of  the  planes  of projection and perpendicular to the third. Thus, Figure 5-39.-Use of “box construction” in isometric drawing. 5-21







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