1 2 Position of Joint lines
Page 31
The following diagram
shows a pipe socket cut at
an angle-Table 1.
Figure I: Shows the elevation.
Figure II: Development, the
seam is on the outside, on line
A-a.
Figure III: Development, the
seam is on the inside, on line
G-g.
Figure IV: Development, the
seam is on the side, on line D-
d.
In figure 1, I first draw the
elevation of the pipe socket.
This is done by first drawing
the horizontal line AG. Next
draw the line D-d at an angle
of 60º to AG. When the
centreline length of D-d has
been determined, draw the
baseline a-g at right angles to
the centreline as shown. Draw
the semicircle with the centre
at point d on the middle line
of the pipe and divide into 6
equal parts. This gives us
points 1-7 on the arc. Then
draw parallel lines to the
middle line through points 1,
2, 3, 4, 5, 6 and 7, thus finding
points a to g and A-G.
The Development of Figure
2
On the base line lay off the
line segment 1 to 2 (of the arc
in figure 1) 12 times. This
gives us points a to g or the
circumference of the pipe
socket. Draw the
perpendicular lines at these
points and lay off the
respective line segments of
figure 1, i.e. aA, bB, cC, etc.
The connecting line of these
newly found points is a curve.
It is very important when
stepping off the 12 equal arc
lengths or divisions not to
accumulate an error which
would make the circumference
longer or shorter than
required. The developments
for figure III and figure IV are
obtained in the same way.
Note: The pipe can also be
developed by calculating it’s
circumference (diameter x π)
and then by dividing the
circumference in half,
quarters, and then each quarter
into three equal and accurate
divisions with no
accumulation
or error.
1.2 Position of Joint lines
We always aim to put the joint
line on the shortest side. The
reason it is put there is to save
time and effort. Sometimes we
put the joint elsewhere for
appearances of a job or to
maximize use of metal. On the
development shown above the
joint is positioned on the line
A-A as this is the shortest side
of the pattern.