Two basic operations — folding and bending — transform flat sheet-metal into a shaped object. With sheet metal of 24-gauge or lighter, you can form the curves of metal cylinders and the sharply-folded corners of boxes by hand.
Before you can form final shapes, you must fold the hems and seams indicated by the pattern to reinforce and bind the cut edges of the flat metal sheet and to make them less hazardous. You can form these folds with a hand seamer while the sheet is After flat edges for the rims of cylindrical objects before shaping the sheet metal. On more complex sheet-metal shapes, such as boxes, cones, and tapers, add the wired edge after you complete the shaping and seaming operations. When forming a box, make sure to form on the flat sheet the open folds where the wire will be fitted.
For folded and grooved seams, use a hand seamer to make open-edged folds, called seam locks, before you shape the flat sheet. Leave clearance under the folds so that the layers of metal slip together easily on the finished object. Form the folds On opposite sides of the flat sheet so that they interlock.
After forming the seam locks, your net step is to make the sharp bends that define the corners of boxes and rectangular forms, and make the curved bends that shape cylinders and tapered shapes. For each kind of bend, use the appropriate stake, or you Can improvise with pipes, blocks, and angle irons. To make an angular bend, for instance, secure the metal with an angle iron and clamps and crease it over the edge of the workbench. Form the sides of a box with the help of a Wooden block that is cut to size and clamped to the bottom of the box. Bend up the against against the wood.
A length of pipe clamped firm in a vise is an adequate substitute for stakes in shaping curves, cones, and tapers. For unusual or complex curves, cut wooden formers — interlocking blocks of hardwood — in the shape you need. Clamp the two pieces of Wood with the metal between them and use the vise to squeeze the Sheet Metal Parts into the shape.
After you've bent and folded the metal into its final form, secure the seams by hooking the seam locks and then hammering them flat to form folded seams. To seam projects with polished sides, clamp a piece of pipe in a vise to support the For boxes or open-ended rectangles, support the workpiece by attaching a length of flat bar stock or railroad rail to the edge of the bench.
For a very secure seam, finish the joint with a hand groover. Select a grooving tool with a slot about 1/16-inch wider than the seam itself. If you are forming a number of objects with grooved seams, settle on a common seam For example, if you plan for 1⁄4-inch seams throughout the project, you can then finish every seam with a standard 5/16-inch (No. 2) hand groover.
Some metal-shaping operations present special problems. Attaching the base of a container to a cylindrical or tapered wall with a double seam, or wiring the rim of a tapered object, requires that you make sharp folds along curved rims and edges. a pair of flat-nosed pliers provided that you wrap the jaws in masking tape to avoid marring the metal. Use a mallet and a setting hammer to crimp the folded metal around a wire to form a wired edge, or for locking the flanges in In a whole, tool and work slowly and patiently to avoid stretching or kinking the metal.