AUXILIARY   VIEWS - 14069_167

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with the right side parallel to the profile plane. The  block  is  then  drawn,  using  all  six  views  of multi-view   projection. By  careful  examination  of  figure  5-22,  you  will see  that  the  lines  AB,  AE,  BD  and  BC  and  the surfaces  ABC,  ABE,  and  BDE  are  oblique  to three regular planes of projection. The lines are foreshortened and the surfaces are not shown in their   true   shape   in   any   of   the   six   normal views. The first step in the drawing of any auxiliary view is to draw the object in normal multi-view projection, as shown in figure 5-23. A minimum of two orthographic views is necessary. The space between  these  views  is  generally  greater  than normal.  The  reason  for  this  will  become  apparent. Notice  in  figure  5-23,  in  the  front  view,  that  A is  the  end  point  of  line  AE  (top  view)  and  C  is the  end  point  of  CD. The  second  step  is  to  decide  which  line  or surface is to be shown in an auxiliary view and which  orthographic  view  it  will  be  projected  from. The  following  facts  must  be  considered  when rendering this decision: 1.  Front  or  rear  auxiliary  views  are  always projected  from  a  side  view. 2.  Right  or  left  auxiliary  views  are  always projected  from  a  front  view. 3.  An  elevation  auxiliary  view  is  always projected  from  the  top  view. The  third  step  is  to  select  the  auxiliary  and reference planes. The auxiliary plane is simply a plane  parallel  to  the  desired  line  or  lines representing an edge view of the desired surface. In figure 5-24, the true length of line AB and the true shape of surface ABE are desired. A left side auxiliary view is needed. The auxiliary plane is drawn parallel to line AB in the front view. Line AB  actually  represents  an  edge  view  of  surface ABE.  The  reference  plane  (top  view)  represents an  edge  view  of  the  orthographic  view  (front  view) from which the auxiliary view will be projected. Therefore,  when  front,  rear,  or  side  auxiliary views  are  desired,  the  reference  plane  will  always be in the top view. When elevation auxiliary views are drawn, the reference plane may be in any view in  which  the  top  view  is  represented  by  a  straight line. The reference plane in figure 5-24 is the edge of  the  top  view  that  represents  the  front  view. Remember   that,   although   these   planes   are represented  by  lines,  they  are  actually  planes running  perpendicular  to  the  views. Step  four  is  to  project  and  locate  the  points describing   the   desired   line   or   surface.   Draw the  projection  lines  from  the  orthographic view   perpendicular   to   the   auxiliary   plane. Then  take  the  distances  from  the  reference  plane, whether  by  scaling  or  with  a  compass.  The distances  are  the  perpendicular  distances  from the reference plane to the desired point. In figure 5-24, the projection lines are drawn from points A,  B,  and  C  in  the  front  view,  perpendicular  to the   auxiliary   plane.   The   projection   line   from point  A  indicates  the  line  on  which  point  E will  also  be  located.  The  projection  line  from point  C  designates  the  line  of  both  C  and  D, and  that  from  B  locates  B  only.  To  transfer the   appropriate   distances,   first,   look   for   any points   lying   on   the   reference   plane.   These points   will   also   lie   on   the   auxiliary   plane where their projection lines intersect it (points A and  C).  To  locate  points  B,  D,  and  E,  measure the  perpendicular  distances  they  are  from  the reference  plane  in  the  top  view  and  transfer these distances along their respective projection lines   in   the   auxiliary   view.   The   points   are equidistant from both the reference and auxiliary planes.   Therefore,   any   line   parallel   to   the reference  plane  is  also  parallel  to  the  auxiliary plane  and  equidistant  from  it. The   fifth   step   is   to   connect   these   points. When  the  total  auxiliary  view  is  drawn,  it  is sometimes hard to discern which lines should be indicated as hidden lines. A rule to remember is as  follows: Those  points  and  lines  lying  furthest  away from the auxiliary plane in the orthographic view being projected from are always beneath any point or  line  that  is  closer.  In  figure  5-24,  point  C (representing  line  CD)  in  the  front  view  is  further from the auxiliary plane than any line or surface it  will  cross  in  the  auxiliary  view.  Therefore,  it will appear as a hidden line. The  final  step  is  to  label  and  dimension  the auxiliary  view.  The  labeling  must  include  an adequate  description.  The  term  AUXILIARY must  be  included  along  with  the  location  of  the view in relation to the normal orthographic views (LEFT   SIDE   AUXILIARY   VIEW,   REAR ELEVATION   AUXILIARY   VIEW,   and   so forth).  Dimensions  are  given  only  to  those  lines appearing  in  their  true  length.  In  figure  5-24, only lines AB, AE, and BE on the auxiliary view should  be  dimensioned. 5-15

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