Figure 2-47.Making a double seam on a cylindrical section.
Beading. BEADING (fig. 2-48) is used to give
added stiffness to cylindrical sheet-metal objects for
decorative purposes, or both. It can be a simple bead
or an ogee (S-shaped) bead. They are made on the
rotary machine using beading rolls.
Crimping. CRIMPING (fig. 2-49) reduces the
diameter of a cylindrical shape, allowing it to be
slipped into the next section. This eliminates the need
for making each cylinder with a slight taper.
Figure 2-48.Turning a bead with a rotary machine.
In sheet-metal development work, some
fabrication or repair jobs can be laid out directly on
sheet metal. This development procedure, known as
SCRATCHING, is used when the object to be made
requires little or no duplication.
When a single part is to be produced in quantity,
a different development procedure is used. Instead of
laying out directly on the metal, you will develop a
PATTERN, or TEMPLATE, of the piece to be
fabricated and then transfer the development to the
metal sheet. The second development procedure is
what we are primarily concerned with in this section.
Special attention is given to the three primary
procedures commonly used in developing sheet-metal
patterns. They are parallel line, radial line, and
triangular development. We will also discuss the
fabrication of edges, joints, seams, and notches.
PARALLEL LINE DEVELOPMENT
Parallel line development is based upon the fact
that a line that is parallel to another line is an equal
distance horn that line at all points. Objects that have
opposite lines parallel to each other or that have the
same cross-sectional shape throughout their length are
developed by this method
To gain a clear understanding of the parallel line
method, we will develop, step by step, a layout of a
truncated cylinder (fig. 2-50). Such apiece can be used
Figure 2-50.Truncated cylinder.
Figure 2-49.A crimped section.