Figure 12-59.--Power-driven squaring shears.
punch a hole in the center of the circle to be cut. Then
Squaring shears are equipped with devices that
serve as stops for sheets when more than one piece of
work your way out to the line of the circle and follow
the same size is required. The stops or gauges are
the line around until the cut is completed.
located on the front, back, and sides of the bed of the
Unless otherwise specified, snips for cutting sheet
shear. They can be adjusted to various lengths and
metal are intended for use on mild steel of relatively
light gauge. Stainless steel and other special alloy steels
Squaring shears are also equipped with hold-downs
must be cut with special snips or shears that have special
for clamping the sheet in place. The hold-downs used
tool steel inlaid edges.
on powerdriven squaring shears are automatic. After
Some ships have squaring shears installed to use in
the machine has been started and allowed to reach its
making long straight cuts on heavy materials. The type
operating speed, the metal is inserted; a foot treadle is
of squaring shear installed depends on the nature and
then tripped, and the machine automatically clamps the
the amount of work to be done on that ship. Repair ships
sheet into position and makes the cut. Hand operated
have large power-driven squaring shears such as the one
hold-downs are usually used on treadle-operated
shown in figure 12-59.
squaring shears. The sheet to be cut is inserted, the
hold-down handle is adjusted, and the cut is then made
Squaring shears are designed for various capacities,
by depressing the foot treadle. After the cut has been
which must never be exceeded. Nameplates indicating
made, the hold-downs are released and the sheet can
the maximum thickness of material to be cut are
then be removed from the machine.
installed on each machine by the manufacturer. In
general, the thickness specified by the manufacturer is
The principle of the shear is shown in figure 12-60.
for low-carbon or mild steel. If alloy steel must be cut,
The lower blade of the shear is stationary and is attached
the thickness of the alloy steel also must not exceed that
in a parallel position to the bed of the machine. The
upper blade, which is the movable blade, is attached to
specified by the manufacturer.