How to Working With Sheet Metal Machinery?
Working with sheet metal, especially after it's been cut, can be dangerous. Each cut you make exposes sharp edges and creates burrs that can slice a finger. That's why it's vital that you take safety precautions. Wear safety gloves whenever possible, and always wear safety goggles and work boots. Never run your hands, even when gloved, over a cut edge. Always file down burrs promptly. Keep your work surface free of scrap. Metal waste also has hazardous edges. Handle metal sheets with care, especially if they are wet, because moisture mixed with oil and dirt can slick the surface and make it hard to grasp. Finally, make sure your hammers are solid and your shears are sharp.
Light sheet metal — metal rolled thin enough to be shaped with hand tools — is one of the most versatile materials for home-improvement projects. It sheathes the roofs and sides of buildings, and it forms gutters and flashing, ductwork, and exhaust hoods. It can be rolled into cylinders, folded into boxes and, depending on the kind of metal, used for objects that are both decorative and practical.
Sheet metals of stainless steel and copper are prized for their luster, aluminum for its light weight and resistance to rust, and galvanized steel — steel with a coating of zinc to forestall rust — for its low cost and easy handling properties. Galvanized steel is the metal of choice for most household projects.
All sheet metals come in a range of thicknesses up to ¼ inch — the point at which sheet metal becomes known as plate. But the measuring systems for thicknesses vary. For stainless and galvanized steel, manufacturers use measurements in decimal parts of an inch or gauge numbers. The gauge is based on the United States Standard system for iron and steel sheet. The lower the gauge number, the greater the thickness.
For aluminum sheet, makers use measurements in decimal parts of an inch to indicate thickness. They generally class copper by weight, in ounces per square foot. For example, flashing on commercial roofing uses 16-ounce (.02 inch thick) copper; decorative items such as exhaust hoods use 24-ounce (.032 inch) copper.
A Gallery of Sheet-Metal Stakes
Sheet-metal workers use iron posts called stakes to support the metal while they work on it. The rounded end of a hollow mandrel stake supports pipes, buckets, and similar articles with curved sides during seaming, grooving, and finishing. The squared anvil at the stake's other end provides a surface for seaming and finishing boxes and rectangular ducts. Use the hatchet stake to make angular folds, such as at the corners of a box. Its sharp edge creases metal crisply. The two horns of different diameters on the conductor stake shape curves and cylinders of various sizes. Shape broad cones and tapered objects on the shorter horn of the blowhorn stake. The slender horn is used for shaping longer and narrower cones.
The shanks of the hatchet, conductor, and blowhorn stakes fit into holes on a steel bench plate, which you can bolt to your workbench. Or you can clamp the stakes in a vise. The hollow mandrel stake attaches directly to your bench with a bolt that slides in a groove on the underside of the tool, allowing varying lengths of the stake to extend over the edge of the bench.
Drafting a Pattern and Transferring to Sheet Metal
Pipes, ducts and containers made of sheet metal can be fully described by a paper pattern. The pattern, often called a stretch-out, has to include all of the seams, folds, and hems that you would need to fold it into the exact shape of the sheet-metal object you want to make. The process of creating a precise and fully detailed pattern is called "drafting."
Cutting Sheet Metal
Cutting sheet metal to the shape and size you need is the intermediate step in fashioning any sheet-metal object — the step between laying out the pattern and bending and fastening the metal into its final form. Because of its relative thinness and flexibility, you can cut sheet metal up to 22-gauge with hand tools almost as effortlessly as you would cut paper with scissors. Use a hacksaw to cut thicker sheet metal, like metal plate.
Aviation snips are the most common tools for cutting both straight and curved lines. A metal punch is another way to cut sheet metal. Both snips and punches require maintenance. You should sharpen them periodically. Keep the joints of your snips well adjusted by tightening the pivot bolt that holds the sides of the tool together. To keep the snips working smoothly, occasionally oil this joint with household oil or a silicone lubricant.
A few power tools work well as sheet-metal cutters. For cutting holes of various sizes, you can use a hand-held electric drill or a drill press fitted with special bits for sheet metal. For cutting large patterns that have either straight or curved lines, you can use a hand-held power shear or a band saw.
Before using a band saw to cut metal, be sure its parts are adjusted correctly. First adjust the blade tension according to the saw manufacturer's instructions. The blade guides, which flank the blade on either side, should be tightened directly against the blade, then loosened until you can slip a piece of paper between each guide and the blade.
How to Bend and Fold Sheet Metal using Metalworking Tools
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 still flat. Finish wired 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. However, 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 sides against the wood.
A length of pipe clamped firmly 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 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 curved sides, clamp a piece of pipe in a vise to support the operation. 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 size. For example, if you plan for ¼-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. You can use 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 together in a double seam. In turning a flange with pliers, as in shaping sheet metal with any hand tool, wear gloves and work slowly and patiently to avoid stretching or kinking the metal.
Metal Shears, Punches and Other Metalworking Hand Tools Used to Cut Sheet Metal
These hand-held snips, shears, and punches are used for cutting sheet metal to any shape or size. There are three standard types of aviation snips:
Aviation snips with a serrated blade that are curved and beveled to cut a straight line
Aviation snips with a right-hand curve
Aviation snips with a left-hand curve
Widely available brands of aviation snips have color-coded grips for quick identification in the workshop. The shape of the metalworking tool blades helps the metal to curve away from the tool as its cut, which allows the cut to progress more easily.
Hawk-billed snips have long handles and slender blades, making them especially useful for cutting curves in tight spots.
The ripping shear is handy for short, hard-to-reach inside cuts.
Punches, when tapped repeatedly with a ball-peen hammer, make holes of various sizes:
Using a hand seamer or sheet metal 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 butt against the metal edge. Use the edge of the lower jaw as a fulcrum by pressing down firmly 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 of the piece to either side, grasping and bending the metal edge every 3 to 4 inches along the fold line. To avoid 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.