11. Set your dividers equal to one of the numbered
of a five-piece 90-degree elbow. Take a pair of dividers
divisions in the half-plan.
and a straightedge and develop a five-piece 90-degree
elbow using this method.
12. Step off twice the number of equal spaces in
the stretchout that you have in the half-plan.
1. Using figure 12-42 as a guide, scribe horizontal
line AB. From point A, scribe line AC to form angle
13. Erect perpendiculars from the base line of the
CAB, which should be equal to the degree of angle that
stretchout and number them as shown in figure 12-42.
the elbow is to be. In this cast, we will use 90 for our
The number with which you begin and end in your
elbow.
stretchout will determine the location of the seam in the
2. Set the dividers for the throat radius and scribe
finished elbow. The best location for a seam on an elbow
the arc, using A as the vertex.
is on the side, so you would number from 4 up to 7, then
down to 1 and back up to 4. Numbering from 1 to 7 and
3. Set your dividers for the heel radius, and using
back to 1, as was shown in the previous development,
A as the vertex, scribe the heel arc. (The heel radius is
would place the seam on the heel. A layout done in this
determined by adding the diameter of the elbow to the
manner is undesirable because it would require more
throat radius.)
time and material to complete the seam. Numbering
4. Divide the heel arc BC into equal spaces. To
from 7 to 1 and back to 7 is also undesirable. This
determine the number of spaces to use and the degree
method would put the seam in the throat of the elbow;
of angle per space, follow this rule: Multiply the number
normally it would be too small to make a strong seam.
of pieces in the elbow by 2 and subtract 2. This will give
The location of the scam is a matter of preference and
you the number of equal spaces. Then, divide the degree
is determined by the job you are laying out.
of the elbow by the number of equal spaces. You now
14. To transfer the pattern from the elevation to the
have the degree of angle for each space on the heel arc.
stretchout using dividers, follow these steps:
SAMPLE:
a. Using line 4, measure its distance between
5 2 = 10 - 2=8
lines AB and HJ with your dividers.
90 8 = 11.25 of angle per space.
b. Using this distance, mark off three spaces on
each of the three lines that are numbered as
5. Now, draw lines from the vertex A to the points
4 in the stretchout. Start from the base line
stepped off on the heel arc, making pieces I and V equal
to one space each on the heel arc. Pieces II, III, and IV
of the stretchouts.
are made equal to two spaces each on the heel arc. They
c. The point on each line 4 that would divide
are twice the size of I and V.
the second and third space in half forms the
6. Using AB for the base line, construct the
center of the stretchout. To make the center
half-plan.
line AB for the stretchout, draw a line to
connect these three points.
7. Step off the circumference of the half-plan into
equal spaces, and number the dividing lines from 1 to
d. Now, using the point where the center line
7. For a larger diameter, use a greater number of equal
and the numbered lines (elements) in the
spaces. The more spaces you use, the more accurate
stretchout intersect, scribe arcs cutting each
your plan will be.
of the lines the same length as the
corresponding lines in the elevation between
8. Use AG for the miter line. You have now
the base line AB and line HJ.
completed your elevation for making the stretchout of
piece II, which will be the same for III and IV, and for
e. Connect these points with smooth lines that
making the stretchout of piece I, which will be the same
will be curved. Your stretchout is now
as V.
completed. Piece I in the stretchout (the
lower piece) is the pattern for pieces I and V
9. To join the elbow together, you must make
in the elbow, and piece II in the stretchout is
allowance for your elbow seam. Add the allowance
the pattern for pieces II, III, and IV.
from line AG up and draw line HJ.
Figure 12-43 is a pictorial view of the five-piece
10. Extend line AB to the right of the elevation to
elbow you have just laid out.
make the stretchout.
12-16
