Developing  the  Patterns

This  is  shown  in  detail  in  Fig.  165,  in  which  the  center  line
of  the  boot  is  first  drawn  as  shown  by  a  3'  8'  e,  making  the
angles  as  desired.  Bisect  these  angles  to  obtain  a  true  miter


FURNACE  FITTINGS  213

line  as  follows :  From  3'  as  center,  with  any  desired  radius,  draw
short  arcs  intersecting  the  center  line  at  a  and  b ;  then  using  a
and  b  as  centers,  with  a  radius  slightly  greater  than  before,  draw
the  arcs  intersecting  at  c,  and  draw  the  miter  line  indefinitely
from  c  through  3'  as  shown.  In  a  similar  manner  obtain  the
miter  line  /  6'  by  means  of  the  arcs  d,  e  and  /.  Now  place  the
half  profile  of  the  round  pipe  at  the  lower  end  of  the  boot,  on
the  line  I  5,  and  the  half  profile  of  the  "oval"  pipe  on  the  upper
end  as  shewn  on  the  line  A  B.  Space  the  semi-circles  in  both
profiles  into  the  same  number  of  parts,  as  indicated,  and  at
right  angles  to  I  5  and  A  B  respectively,  draw  lines  from  the
various  points  2  to  4  and  10  to  6  until  they  cut  the  miter  lines
i'  5'  and  6'  10'  as  shown.  Connect  by  lines  the  points  i'  and  10'
and  5'  with  6',  which  completes  the  side  elevation.  The  half
pattern  for  the  round  and  "oval"  pipes  will  be  laid  out  by  parallel
lines  as  follows :  Extend  the  line  i  5  in  the  side  elevation  as
shown  at  the  right  by  C  D,  upon  which  place  the  girth  of  the
half  profile  of  the  round  pipe  as  shown.  From  the  small  figures
erect  lines  at  right  angles  to  C  D,  and  intersect  same  by  lines
drawn  parallel  to  C  D  from  the  various  points  i'  to  5'  on  the
miter  line  in  elevation.  Trace  a  line  through  the  intersection
thus  obtained;  then  will  i"  5"  5  i  be  the  half  pattern  to  which
the  edges  must  be  allowed  for  seaming.
