The steps used to make a ring by this method are as
follows:
1. Scribe the inner and outer concentric circles
using the desired radii.
2. Make a series of straight cuts on the slitting
shears as close to the outer circumference as possible.
3. File or grind the outer circumference down to
the scribed line.
4. Drill, punch, or chisel the inner material from
the disk. Take care not to work too close to the inner
scribed line.
A throatless shear is a heavy-duty machine that can
take material up to l/4 inch in thickness. Smaller
Figure 12-67.--Cutting light sheet metal with a cold chisel.
power-driven and hand-operated models are available.
The throatless shear is normally used to cut out shapes
that have an irregular curved edge. There are no guides
on this type of machine. You control the cut by changing
the direction of the sheet so that the blades cut along the
lines scribed on the material.
There is a wide varity of equipment for cutting sheet
metal. However, you may be assigned to a ship that does
not have the equipment nor the room to keep it. In this
case, you will have to depend on your normal shop tools.
You can do a number of simple cutting operations on
light sheet metal while the material is held firmly in a
bench vise. Figure 12-67 shows the method used to cut
sheet metal, held firmly in a vise, by using a chisel and
hammer. Also you may use a hacksaw to make some of
the cuts on the sheet metal held in a vise.
FORMING SHEET METAL
Sheet metal may be formed either by hand or with
Figure 12-68.--Hand forming a bend in sheet metal.
the aid of various special tools and machines. The hand
forming of a bend is shown in figure 12-68.
The sheet is laid on a workbench or other flat
surface, with the required amount projecting over the
edge. A piece of angle iron is laid on top of the sheet
with its edge even with the edge of the workbench.
C-clamps are used to hold the angle iron and the sheet
in place. Form the bend first by bending the entire length
of the sheet with your hands. Then finish the bend by
striking the bend area with a wooden mallet.
Sheet Metal Brakes
Sheet metal brakes produce more uniform bends
than those made by hand. They also require
considerably less effort. A standard cornice brake is
shown in figure 12-69. Before you use this machine,
Figure 12-69.--Standard cornice brake.
two adjustments must be made.
12-29
