Squaring shears are used for cutting and squaring sheet metal. See figure 13-17. They may be foot operated or power operated. Squaring shears consist of a stationary blade attached to a bed and a movable blade attached to a crosshead. To make a cut, place the work in the desired position on the bed of the machine. Then use a downward stroke to move the blade. Foot-powered squaring shears are equipped with a spring that raises the blade when foot pressure is removed from the treadle. A scale graduated in fractions of an inch is scribed on the bed. Two side guides, consisting of thick steel bars, are fixed to the bed, one on the left and one on the right. Each is placed so that its inboard edge creates a right angle with the cutting edge of the bed. These bars are used to align the metal when square corners are desired. When cuts other than right angles are to be made across the width of a piece of metal, the beginning and ending points of the cut must be determined and marked in advance. Then the work is carefully placed into position on the bed with the beginning and ending marks on the cutting edge of the bed.

Figure 13-17.-Squaring shears.

A hold-down mechanism is built into the front of the movable cutting edge in the crosshead. Its purpose is to clamp the work firmly in place while the cut is being made. This action is quickly and easily accomplished. The handle is rotated toward the operator and the hold-down lowers into place. A firm downward pressure on the handle at this time should rotate the mechanism overcenter on its eccentric cam and lock the hold-down in place. You should reverse the action to release the work.

Three distinctly different operationscutting to a line, squaring, and multiple cutting to a specific sizemay be accomplished on the squaring shears. When you are cutting to a line, place the beginning and ending marks on the cutting edge and make the cut. Squaring requires a sequence of several steps. First, square one end of the sheet with one side. Then square the remaining edges, holding one squared end of the sheet against the side guide and making the cut, one edge at a time, until all edges have been squared.

When several pieces are to be cut to the same dimensions, you should use the adjustable stop gauge. This stop is located behind the bed cutting edges of the blade and bed. The supporting rods for the stop gauge are graduated in inches and fractions of an inch. The gauge bar is rigged so that it may be set at any point on the rods. With the gauge set at the desired distance from the cutting blade, push each piece to be cut against the stop. This procedure will allow you to cut all pieces to the same dimensions without measuring and marking each one separately.

NOTE: After you cut the first piece in a series, measure it to make sure that the stop is accurately set.