bent to the desired angle. If a large amount of metal
extends beyond the bending blocks, you should
maintain enough hand pressure against the protruding
sheet to prevent the metal from bouncing. Remove any
irregularity in the flange by holding a straight block of
hardwood edgewise against the bend and striking it
with heavy blows of a hammer or mallet. If the amount
of metal protruding beyond the bending blocks is small,
make the entire bend by using the hardwood block and
a hammer.
Figure 4-34.--Preparation for straight bend by hand.
Curved flanged parts have mold lines that are either
concave or convex. The concave flange is formed by
workbench. The stake holder contains a variety of holes
stretching, while the convex flange is formed by
to fit a number of different types of shanks. Although
shrinking. Such parts are shaped with the aid of
stakes are by no means delicate, they must be handled
hardwood or metal form blocks. These blocks are made
with reasonable care. They should not be used as
in pairs and specifically for the shape of the part being
backing when you are chiseling holes or notches in
formed. Each pair conforms to the actual dimension
sheet metal.
and contour of the finished article.
Bending in a Vise
You should cut the material to be formed to size,
allowing about one-quarter inch of excess material for
Straight-line bends of comparatively short sections
trim. File and smooth the edges of the material to
can be made by hand with the aid of wooden or metal
remove all nicks caused by the cutting tools. This
bending blocks. After the part has been laid out and cut
reduces the possibility of the material cracking at the
to size, you should clamp it along the bend line between
edges during the forming operation. Place the material
two form blocks, which are held in a vise. The form
between the form blocks and clamp it in a vise so that
blocks usually have one edge rounded to give the
the material will not move or shift. Clamp the work as
desired bend radius. See figure 4-34. By tapping lightly
closely as possible to the particular area being formed
with a rubber, plastic, or rawhide mallet, bend the metal
to prevent strain on the form block and to keep the
protruding beyond the bending block to the desired
material from slipping.
angle.
Concave surfaces are formed by stretching the
You should gradually make the bend even. Start
material over a form block. See figure 4-35. You should
tapping at one end and work back and forth along the
use a plastic or rawhide mallet with a smooth, slightly
edge. Continue this process until the protruding metal is
Figure 4-35.--Forming concave hand bend.
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