Drawing  an  angle  in  isometric

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Figure 5-40.-A non-isometric line (AB) in an isometric projection. a  NON-ISOMETRIC  LINE  is  a  line  that  is  not parallel   to   any   one   of   the   three   legs   of   the isometric axis. It is not a normal line in a normal multi-view  projection  of  the  object. The  upperpart  of  figure  5-40  shows  a  two- view  normal  multi-view  projection  of  a  block. Though the line AB is parallel to the horizontal plane  of  projection,  it  is  oblique  to  both  the vertical  and  the  profile  planes.  It  is  therefore not  a  normal,  but  an  oblique,  line  in  the  multi- view  projection,  and  it  will  be  a  non-isometric line in an isometric projection or drawing of the same  object. The   line   AB   appears   in   its   true   length in the top multi-view view because it is parallel to  the  plane  of  the  view  (the  horizontal  plane); but   it   will   appear   as   a   non-isometric   line, and  therefore  not  in  its  true  length,  in  an isometric   drawing,   as   shown   in   the   bottom part  of  figure  5-40.  It  follows  that  you  cannot transfer   AB   directly   from   the   multi-view projection  to  the  isometric  drawing.  You  can, however, transfer directly all the normal lines in the multi-view projection, which will be isometric lines   appearing   in   their   true   lengths   in   the isometric drawing. When you have done this, you will have constructed the entire isometric draw- ing,  exclusive  of  line  AB  and  of  its  counterpart on the bottom face of the block. The end points of  AB  and  of  its  counterpart  will  be  located, however, and it will only be necessary to connect them by straight lines. Angles in Isometric.—In  a  normal  multi-view view of an object, an angle will appear in its true size.  In  an  isometric  projection  or  drawing,  an angle never appears in its true size, Even an angle formed  by  normal  lines,  such  as  each  of  the 90-degree corner angles of the block shown in the bottom  part  of  figure  5-41,  appears  distorted  in isometric. The   same   principle   used   in   transferring a  non-isometric  line  is  used  to  transfer  an angle in isometric. The upperpart of figure 5-41 shows   a   two-view   multi-view   projection   of   a block.  On  the  top  face  of  the  block,  the  line AB  makes  a  40-degree  angle  with  the  front edge.  The  line  AB  is  an  oblique  (that  is,  not normal)  line,  which  will  appear  as  a  non-isometric line in the isometric drawing. You locate the end points  of  AB  on  the  isometric  drawing  by Figure  5-41.-Drawing  an  angle  in  isometric. 5-22

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