may be drawn from O at any convenient angle.All three are equal in length, the length being thelength of an edge of the original cube (which maybe scaled down or up if the drawing is made otherthan full scale). After you draw the axis,complete the projection by drawing the requiredparallel lines. All the edges shown in theprojection are, like the edges on the original cube,equal in length.Cabinet ProjectionThe first thing you notice about the cubeshown in figure 5-48 is the fact that it doesn’t looklike a cube because the depth dimension appearsto be longer than the height and width dimensions.The reason for this is the fact that a cavalierprojection corrects a human optical illusion—theone that causes an object to appear to becomesmaller as its distance from the eye increases. Thisillusion. in turn. causes receding parallel lines toappear to the eye to be shorter-than they reallyare, and also to be converging toward a point inthe distance. But receding parallel lines on acavalier projection appear in their true lengths,and they remain constantly parallel. Also, the faredges of the cube shown in figure 5-48 are equalin length to the near edges.The distortion in figure 5-48 is only apparent.It is sometimes desirable to reduce this appearanceof distortion. This can be done by reducing thelength of the receding axis (OC in fig. 5-39).Thisaxiscanbereducedbyanydesiredamount,butitiscustomary toreduce itbyonehalf.Figure 5-49.-Cabinet projection of the cube in figure 5-48.(Note receding axis OC reduced by one half itslength.)When the receding axis is reduced by one half,the projection is called a CABINET PROJEC-TION. Figure 5-49 shows a cabinet projectionof a cube. The length of the receding axis OC hasbeen reduced by one half. As you can see, thisrepresentation looks more like a cube.Cavalier and cabinet projections are comparedin figures 5-50 and 5-51.Oblique Drawing TechniquesIn an oblique projection drawing of arectangular object, one face (usually the mostprominent or most important) is parallel to theplane of projection. All features appearing on thisplane, such as circles or oblique lines, are in theirtrue dimension. However, in the side or top views,these same features are somewhat distortedbecause of the receding axis angle. When drawingthese features, you can use various techniques toaid you in their construction.For convenience, the angles chosen for thereceding axis are either 30 degrees, 45 degrees, orFigure 5-50.-Cavalier projection. Distances along front axisand along receding axis are all true.5-26
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
