Using a hand seamer or Sheet Metal Parts seamer, grasp the middle of the edge of sheet metal you are going to bend, positioning the jaws of the seamer so that they close at the fold line previously scribed on the metal. Tighten the adjusting screws until they Use the edge of the lower jaw as a fulcrum by pressing down firm against the work surface while you lift the handles of the seamer to start the bend. On a long edge, it is best to work from the middle To the kinking the metal, bend each section only slightly, and then move on to the next section of metal, bringing it even with The previous section. Continue folding bit by bit until you have worked the edge to an angle halfway between vertical and completely closed. The edge is now ready for wiring, or for further creasing to form a folded hem or a seam lock. Measuring Correctly for Seams in Sheet Metal In sheet metal work, the extra material needed for each seam depends on the size of the seam, the number of folds it relates, and the thickness of the metal. For a 1-inch standing seam, typical on a large duct, you need Inch...? inch extra metal for the edge with the single fold, and 1a...? inches extra for the edge with the double fold, plus a bit extra for the thickness of the metal. When you are planning for folded or grooved seams, both of which are typically 1?4 inch wide, allow for 1?4-inch folds on each edge, plus a small additional amount to accommodate the thickness of the folds. When you're using a folded seam Or a grooved seam to join the lengthwise edges of a duct or a pipe, be sure that you enlarge the pattern by the width of the seam — in this case 1?4 inch — to allow for the reduction in circumference caused by the seam. A standard 1?4-inch double seam requires a 1?4-inch allowance along the wall of the container where you will join the wall to the base. You need 1?2 inch of extra metal to accommodate the two folds along the edge of the base, along with small additional Allowances for the thickness of the folds.