as one half of a two-piece 0degree elbow. This piece
of sheet metal is developed in the following
1. First, draw a front and bottom view by
orthographic projection (fig. 2-51, view A).
2. Divide half the circumference of the circle
(fig. 2-51, view A) into a number of equal parts. The
parts should be small enough so that when straight lines
are drawn on the development or layout between
division points, they will approximate the length of the
arc. Project lines from these points to the front view, as
shown in figure 2-51, view B. These resulting parallel
lines of the front view are called ELEMENTS.
3 . L a y o f f t h e b a s e l i n e , c a l l e d t he
STRETCH-OUT LINE, of the development to the right
of the front view, as shown in figure 2-51, view C.
Figure 2-51.Development of a truncated cylinder.
4. Divide the stretch-outline into twice the number
of equal parts equal to each division of the
circumference on the half circle of the orthographic
view (fig. 2-51, view C).
5. Erect perpendicular lines at each point, as
shown in figure 2-51, view C.
6. Using a T-square edge, project the lengths of the
elements on the front view to the development
(fig. 2-51, View D).
7. Using a curve (french or other type), join the
resulting points of intersection in a smooth curve.
When the development is finished, add necessary
allowances for warns and joints, then cut out your
RADIAL LINE DEVELOPMENT
The radial line method of pattern development is
used to develop patterns of objects that have a tapering
form with lines converging at a common center.
The radial line method is similar in some respects
to the parallel line method. Evenly spaced reference
lines are necessary in both of these methods. But, in
parallel line development, the reference lines are
parallellike a picket fence. In radial line
development, the reference lines radiate from the
APEX of a conelike the spokes of a wheel.
The reference lines in parallel line development
project horizontally. In radial line development, the
reference lines are transferred from the front view to
the development with the dividers.
Developing a pattern for the frustum of a right
cone is a typical practice project that will help you get
the feel of the radial line method. You are familiar with
the shape of a cone. A right cone is one that, if set
big-side-down on a flat surface, would stand straight
up. In other words, a centerline drawn from the point,
or vertex, to the base line would form right angles with
that line. The frustum of a cone is that part that remains
after the point, or top, has been removed.
The procedure for developing a frustum of a right
cone is given below. Check each step of the procedure
against the development shown in figure 2-52.
1. Draw a cone ABC with line ED cutting the cone
in such a way that line ED is parallel to the base line
BC. EDCB is called a frustum.
2. With center O and radius OB, draw the
half-plan beneath the base line BC. Divide the