first bend to the required angle, set the stop gauge so
1. Adjust the clamping adjustment screw for the
gauge of sheet metal you are going to bend. The
that the bending leaf will not travel beyond this angle.
clamping device holds the work firmly in position,
You can now make as many duplicate bends as are
provided it is adjusted to the correct gauge. For
required.
example, if the clamping device is set for 18-gauge
The standard cornice brake is extremely useful for
sheet and you are bending 24-gauge sheet, the sheet will
making single hems, double hems, lock seams, and
most likely slip and the bend will be formed in the
various other shapes. As examples of how to actually
wrong position. If, on the other hand, you try to bend a
use the standard cornice brake, we will consider first the
thicker sheet while the machine is set for a thinner
forming of a single hem and then the forming of a
gauge, you may break the clamping handle of the
Pittsburgh lock seam.
machine.
To form a single hem (fig. 12-23), proceed as
2. Adjust the machine for the correct bend
allowance. You can do this by moving the upper jaw to
follows:
the correct position for the thickness of the metal and
1. Insert the sheet to be hemmed all the way into
for the radius of the bend to be made. If the upper jaw
the brake. Line up the brake line with the front edge of
is adjusted to the exact thickness of the metal, the bend
the upper jaw.
will be sharp and will have practically no bend radius.
If the jaw is set for a thickness greater than the metal,
2. Raise the lower leaf as far as it will go. If the
the bend will have a larger radius. If the jaw is set for a
stopgauge has been set, be sure the yoke is set far
thickness less than the metal, the jaws of the machine
enough toward the end of the rod to permit the leaf to
may be sprung out of alignment and the edges of the
travel the maximum distance.
jaws damaged.
3. Lower the leaf, release the clamping device, and
After these two adjustments have been made,
remove the sheet from the brake.
proceed as follows:
4. Close the left side of the brake, allowing the
1. Scribe a line on the surface of the sheet metal
right side to remain open.
where the bend is to be.
5. Insert the left hem edge of the sheet into the
2. Raise the upper jaw with the clamping handle
brake, holding the sheet with your left hand. Hold the
and insert the sheet. Bring the scribed line into a position
sheet at an angle to the front edge of the brake.
even with the front edge of the upper jaw.
6. Lower the upper jaw with your right hand. This
3. Clamp the sheet firmly in position. Check to
action will flatten that portion of the hem that is between
make sure the scribed line is still in line with the front
the jaws. The brake is thus being used as a press.
edge of the upper jaw.
7. Raise the upper jaw and decrease the angle
4. Raise the lower leaf to the desired angle for the
between the front edge of the brake and the edge of the
bend or flange. If you are bending soft and ductile metal
sheet. When you decrease this angle slightly, you will
such as copper, the bend will be formed to the angle to
bring another small portion of the hem under the jaws
which you raised the lower leaf. If you are bending
of the brake.
metal that has a good deal of spring to it, you will have
to raise the lower leaf a few degrees higher. This will
8. Continue lowering and raising the upper jaw
compensate for the tendency of the metal to spring back
until the entire hem has been flattened. Do the flattening
after it has been bent. The exact amount of springback
operation in small sections. Do NOT attempt to flatten
that you will have to allow for will depend upon the type
the entire hem in one operation. If you are working very
of metal you are bending.
springy metal, you may have to work the hem part of
5. Release the clamping device and remove the
the way down with a mallet before you can finish it in
sheet from the brake.
the brake.
The standard cornice brake is equipped with a stop
Figure 12-70 shows the procedure for making a
gauge, consisting of a rod, a yoke, and a setscrew. These
Pittsburgh lock seam as follows:
permit you to limit the travel of the bending leaf. This
1. Insert the sheet in the brake, making the first
is a useful feature when you must make a lot of pieces
bend to just a little less than 90 degrees.
with the same angle of bend. After you have made the
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